This is a quick article from the archives that got a big response 4 months ago. I also just did a Facebook Live video this morning baring my soul on the topic of flowing nitrogen in response to an Email.


Why is it called single phase 240 when there are two opposing phases?

I wondered why two 120v opposing phases was called “Single phase 240” for years.

Then someone pointed out to me that a typical “single phase” pole transformer only has one power leg entering and two coming out.

This freaked me out. How can a transformer primary be one phase, a SINGLE sine wave and output two perfectly opposing sine phases?

It’s just two separate winding wraps in OPPOSITE directions on the secondary. Stupid simple, but I just never knew it.

So unlike a three phases services that uses all three power phases from the power supply, the single phase service only uses one. The second phase is “created” in the secondary of the distribution transformer itself and is the same “phase” but opposite.

Pretty cool.

— Bryan

Imagine, if you will, a 20 year old kid. No formal training in the HVAC/R field, just ride along “training” and book learning as he reads along with his journeyman father with whom he’s riding. On one stormy summer evening, a service call comes in for an ice cream freezer down. After calling and talking to the site manager, the old timer decides that this call is within the abilities of this fresh-faced kid, so he throws him the keys and say “Tag!  You’re IT!” and wishes him well.

Flash to that same kid pulling into the parking lot and meeting an anxious manager at the door. “They’re all down.  Everything in frozen foods is down.”

Oh boy!!!   Here we go!

 The heart-dropping sensation those words brought to me are beyond description, but are never far from my memory. That night I learned a lot… That I was capable of much more than I gave myself credit for because I did manage to diagnose the problem (for the most part) and I learned that leak checking is a difficult job. The problem, by the way, was that the relief valve on the receiver had opened, dumping over 500 pounds of refrigerant into the atmosphere.


That is an example of a (mostly) non-preventable leak although I do think that those sorts of leaks are somewhat manageable, and we’re going to explore the various means of finding, repairing and, possibly more importantly, preventing leaks on larger refrigeration equipment.


Let’s start by saying that leak detection, on large refrigeration like I work on every day, is very much a full time job. With dozens of accounts, each one with multiple large pieces of equipment on site, leak detection is an important part of a maintenance program and sometimes, a 24\7 job.


For starters, what are we talking about when I say “large refrigeration equipment”? I’m mostly talking about supermarket rack refrigeration systems. These pieces of equipment can hold anywhere between a couple hundred pounds up to well over a ton of refrigerant. They’re made up of a central pumping station where several compressors work together to maintain a set suction pressure, a condenser unit which is typically mounted on the roof, the various fixtures where the product is stored and importantly, the interconnecting piping system.


A solid leak prevention system starts before a drop of refrigerant is ever added. It starts at installation with good piping practices. Piping should be installed so that it can move naturally with temperature changes without rubbing on supports, where valve openings and closings don’t cause liquid hammer and result in either line movement or breakage (ideally, eliminating that type of condition altogether) and any control lines need to be properly and safely secured to prevent them from vibrating and breaking. If your system is poorly installed, you are going to have more leaks than if the system is properly installed.


For the most part though, that is beyond our control. We’re service guys. We’re called when that installation breaks and we can’t change how the equipment was installed, we just have to deal with it the best that we can. Sometimes we can make small changes such as securing capillary control lines with silicone to prevent them from vibrating against themselves and other things, switching to ‘armored’ cap tubes when we service a part of the machine, etc but these are generally very small changes in the grand scheme of things.


Let’s start with a new customer and we can talk about a multi-step process to find, pinpoint and potentially prevent leaks for that customer.


My first step is to do a customer interview and a quick, gross inspection of the equipment.  I’ll talk to the customer about refrigerant leaks.  Do they have to add a lot of refrigerant?  Are leaks a problem for them? Nothing in hand more than a flashlight usually. I’m looking at refrigerant levels, looking for a pile of empty drums in the corner of the mechanical room or a nice stack of fresh, full ones. I’m looking for puddles of oil or piles of cat litter under the equipment to indicate where a large leak may have occurred and hasn’t been cleaned up. Looking for oil spots, smears and trails on the piping and valves. I’m also looking for those practices I mentioned earlier where piping is visible.


Now, I’ve got an idea of what I’m in for. I’ve got 2” of dirty, oily cat litter under the unit, a dozen empties in one corner and a fresh stack of full cans in the other. The customer is complaining that the ‘other guys’ can’t find any leaks but have to add gas once every week to 10 days and have started to make excuses. One tech actually tried to tell the owner “Well… You see, these new gasses, the molecules are smaller than the old gasses.. That means that the molecules can just leak out of the pipes so you just have to add gas sometimes.”


Shaking my head, I’ll hike out to the truck and fire up the leak detector.


When it comes to leak detectors, I’ve got some opinions based on years of field experience.   I use the H-10PM or the Tif ZX1.   While both have some faults, both have proven to be very reliable and consistent detectors.


So, for step 2, I’m going to turn that detector on at the truck and let it warm-up and go through its calibration out there so that I can be reasonably sure it’s calibrating in a clean environment. The startup and warm up process of a leak detector is also a calibration process. With large units and large amounts of refrigerant, the entire building can be contaminated with refrigerant so starting the detector up in that contaminated environment can be problematic.


If you get an alert as soon as you step through the doors, you have a leak. This is where you have to place a degree of trust in your instrument. It’s telling you there is a leak in that building, it’s up to you to find it.


Start a methodical search of the building, notebook in hand.  If the leak detector alerts in a certain cooler or even a certain area of the store, walk away and revisit that spot, then make a note of the area and move on. We’re just surveying right now, making notes allows us to come back later and work to pinpoint and repair the leaks. Also, while you’re searching, keep a constant lookout for oil spots. You’d be surprised how many leaks I have found by the oil spot rather than the detector.


After all of the fixtures are searched and appropriate notes made, move on to the mechanical room and repeat the search, then move on the the remote condenser. On that condenser because you’re usually outdoors in the wind, very often your eyes are a bigger asset than any leak detector. Look for oily spots, particularly places where dirt and dust has accumulated and is soaked with oil.


Survey done, it’s time to zoom in on each leak and make the repairs, so let’s look at some methods to make that process more simple.


Finding a leak is part skill, part art and all determination. As a skill and an art, it’s something that you develop over time and with practice, but a few pointers can help hone those skills.


First, and I know I’ve said this but it bears repeating, trust your instruments. In this instance, your instrument knows better than you do. If it says there is a leak, you need to believe it and work to find that leak.  Another thing is that you’re looking for a leak, so LOOK. Sometimes you’ll see an oily patch, or a weird bubble where one shouldn’t be. It is those little details that give up a leak.


If I’m prioritizing places to look for leaks, I’m starting with flare fittings. Between poor factory flares, vibration and temperature related expansion and contraction of those fittings, that’s a high likelihood spot to look. Follow that up with just about any mechanical or o-ring seal on a valve.  Those are kind of high percentage spots to look, too


Now, remember that survey we did?   Dig that notebook back out and pick a spot. We’ll get to all of them. Maybe you made a note that one was a large area or the alert on the detector was particularly intense. That’s as good a spot as any to start. Head back to that spot and have a look around. Remember, we’re looking for oil spots and staining first.  Nothing?  Ok, now we have two directions to go in. If it is in a closed box like a walk-in, usually your leak detector isn’t going to be of too much use inside.  The sealed nature of the box tends to concentrate refrigerant making leaks appear larger than they actually are. Start by removing the covers for the ends of the evaporator coil.  Again, look for leaks, then use soap bubbles to try to find it.


In open type cases, it’s a little easier to narrow down the leak. Pass back and forth over the leaking area, resetting the calibration on your detector until you’ve got a narrow band.                           This will have the area of the leak narrowed down then you can start using soap bubbles to pinpoint the leak.


Some people complain about finding little tiny leaks. Very often, the small ones aren’t the tough ones to find.   Sometimes, you get a large leak that is blowing refrigerant far away from the source and you’ll get alerts several feet away from the actual source of the leak. While this can happen almost anywhere, it seems more common in mechanical rooms because of the control hoses and the high vibration there. First thing I’ll do if I suspect a leak like this is shut down everything in the mechanical room. Shut off the compressors, shut off any exhaust fans and start looking. First, without the machinery running, you may well be able to hear the leak. Without all of the air movement, it may be easier to locate the leak.  This trick can be extended to the entire building. Shutting off all HVAC equipment can allow refrigerant that is being circulated to settle near the leak, allowing you to narrow in on it.


Repeat this procedure on each leak until every last one is found and repaired, then start all over again and repeat until no leaks are found on the storewide assessment.


Once we’ve got a leak free system, take the time to clean up the mess in the mechanical room. Clean up that nasty cat litter and clean up the spilled and leaked oil, dispose of the empty drums and stack any full ones neatly and secure them per local and national codes. Take a clean rag and wipe the oily dirt away from other repair sites. Clean equipment means that you can more easily spot a leaky spot because an oil spot is the exception rather than the rule.


Leak detection is a full time job.


You really have to think about the amount of gas we’re dealing with here. Think about how much room 30, 30 pound refrigerant cylinders takes up?  Want to jam those in your truck? Think about the cost of that refrigerant. Now, remember back to when you took your EPA certification. Remember the 35% EPA leak rate trigger? We need to keep leak rates down on larger equipment.


So, how do you treat a store that you regularly service?


Really, a similar process, you just don’t normally have to spend a lot of time tracking down old leaks. Each month, on the preventive maintenance visit, the tech doing the PM does a leak check similar to the survey check outlined before.  If any indications of leaks are found corrective action is taken. If the PM tech has the skills and the tools, he will repair the leak. If not, a more skilled tech should be dispatched to the site to correct the leak and to guide and educate the PM tech. You don’t want to leave leaks go unrepaired, so any leak indication really needs to be followed up on.


Where things get tough is that a PM visit is only a monthly thing while this machine is running 24\7\365 with all of the things that can cause leaks happening on a constant and ongoing basis.It’s very possible for a tech to either miss a leak on a PM or for a leak to form soon after the PM was completed and then that leak just sits, unaddressed for the next 28 days or so.


There are a couple backstops to watch for that.


One method is refrigerant level monitoring. Most of these large machines have sensors in the receiver of various types to monitor the amount of refrigerant in that tank. From a simple float switch to give a digital signal when the level drops below a certain point to analog signals indicating what percentage of the tank is filled, we’re watching this and monitoring it with a digital control system. When the level falls below a predetermined level, an alarm is generated. This can prevent a serious problem resulting in a loss of product by catching the loss of refrigerant before so much refrigerant is lost that it causes problems at the fixture. The drawback of this system is that we can still lose a significant amount of refrigerant before a technician is involved to correct the problem.


Enter continuous refrigerant monitoring………


The newest buildings are being equipped with machinery to continuously sample the air in the building and alert when even small quantities of refrigerant are detected. How this works is that sampling tubes are run throughout the building to areas where refrigeration equipment is. You’ll see sampling tubes under fixtures, sampling tubes located in piping chases, in walk in boxes and around the machinery itself.  A detector pumps air samples through that tubing and checks it for refrigerant and reports in parts per million. When that level exceeds a limit, again an alarm is generated and a technician dispatched to investigate and correct.


These machines need service and calibration as well, so that can mean more work for the technician.


Cracking the tough ones

So, let’s say that we’ve fixed all of the leaks on our initial survery, got the units charged back up to normal levels and we’re still seeing a slow drop in the amount of refrigerant in the rack. We KNOW that there’s a leak somewhere. We bring our detector in the building from a clean calibration out by the truck, it alerts at the door.   Yeah, we’ve got a leak in this building.   A check of the mechanical room, the fixtures and the condenser however, show nothing. Maybe we’re getting an alert in one part of the building so let’s focus our efforts there. First step will be typically be shutting down the air circulation. Kill HVAC equipment, exhaust fans and anything else that’s going to circulate air. Pay attention to smaller fans because sometimes it doesn’t take much air to move that refrigerant around. What we’re looking to do is allow that refrigerant to settle into one area. That’s going to help us to narrow down the location of that leak.


Work methodically, checking every bit of exposed piping, checking under insulation, in chases both overhead and underground and follow every single alert your detector gives. There are no shortcuts to this job. It is tedious, difficult and very often frustrating work. Be patient and methodical in your searching and bring lots of soap and lots of flashlight batteries.


Another common trick used to pinpoint leaks, and this one is usually employed once you’ve got the leak localized to a fairly small area is to raise the system pressure. Turn that system off or close an isolation valve, allowing pressure to build will make a leak form bubbles better. We’ve all tried this sort of trick, even by adding nitrogen to raise the pressure within the unit. No surprise there, right? Let me throw a curveball at you, now… Sometimes, the leak is so large that the system pressure is creating such a large leak that bubbles won’t even start to form because the refrigerant coming out of the leak simply blows the soap away from the leak.

Depending on the location and angle of the leak, you can’t always hear it or at least my old, defective ears can’t. In cases like this, I’ll often lower system pressure closer and closer to atmospheric without going below that. This allows a large leak to be located more easily. Also, back to basic observation techniques, I’ll run my fingers around and over the pipes. Even though I can’t hear the leaks, I can feel the escaping refrigerant gas.


Another problem with very large leaks and electronic leak detectors is that, once a large leak is repaired, the refrigerant in the ambient air doesn’t just ‘magically’ go away.  Sometimes we need to walk away after repairing a large leak, allow the building HVAC system to do its job of circulating air in the building, bringing in some fresh air and diluting the refrigerant in the atmosphere so it doesn’t affect our search for more leaks.


At the beginning, I said that a leak like the one on that service call was ultimately preventable. Again, this is where a comprehensive maintenance program helps a lot.   The ultimate CAUSE of that relief valve opening traced back to a defective high pressure cutout control. A single phase power outage caused the condenser to stop, that resulted in higher than normal head pressure and, had the safety controls been operating normally, the safeties would have shut the compressors down and prevented that problem.  It would have still resulted in a service call, but it wouldn’t have been a 500# refrigerant loss. Detailed and comprehensive service and maintenance procedures include more than just leak checking.

— Jeremy Smith

I was at the AHR conference today walking around and I stopped at the booth of a popular hard start kit manufacturer (especially popular with white shirt sales techs). I listened to the guy behind the booth “training” some municipal maintenance techs on the use of his hard start kit, and to be fair, I actually think it’s a decent kit.

However, I have an issue with what he KEPT SAYING over and over. He kept calling the C terminal on the compressor and the 5 terminal on the potential relay (hard start relay) a “ground”. He even said and I quote here “A 2 wire kit has no ground and should not be used. If you find one like that just tell the customer it has no ground and they will understand it’s unsafe and should be replaced”.


Common and ground are not the same, they have no relation. Common is the common point opposite the run and start terminals, it has nothing to do with ground. Ground is a connection to ground and has everything to do with creating a safe path to ground in the case of short to prevent YOU from becoming that path and killing you.

This is one way that well-meaning people become techs that end up on the news for ripping off grandma.

Once again. I actually agree that 3 wire start kits are the way to go. Just don’t call common ground like a thousand times.

End rant.

— Bryan

When I was a green tech I was really big into showing up all the other techs by doing THE BEST cleaning I possibly could. One of my favorite things to do was to clean the condenser until it was SPOTLESS inside and out. The only issue was, I really liked using that brown coil cleaner (that will remain nameless) in pretty intense concentrations (It was so dramatic to watch it foam).

One day I was washing a Lennox condenser coil and I noticed that it was REALLY DIRTY… it didn’t look dirty at first but the more sprayed it the more black stuff kept coming off… and coming off… and COMING OFF 

It wasn’t dirt, it was a coil coating and now the thing looked HORRIBLE. Lesson learned.

Cleaning HVAC, Refrigeration, Chillers and Ice machines is obviously not a one size fits all solution but all too often we as techs grab whatever we have on the truck and try to make it work. Here are some quick tips.

Read First

I say this in basically every tip, but if you aren’t reading you are ignorant of the risks and best practices of the industry. The manufacturer will mention safe uses, concentrations and hazards right on the bottle. Pay attention to them.

Careful What Goes in the Air

When you spray something on an evaporator coil, inside a case, in an air handler etc… you are putting it in the air people breathe. Are you 100% sure the cleaner you are using is safe for that use? Will it smell like the armpit of Lucifer when you do it? Either way make sure take the proper precautions to ensure you aren’t going to harm or irritate the occupants of the building. Can anybody say liability claim?

Is it coated?

Cols can be coated with many possible coatings and they all respond differently to acidic or alkaline cleaners. When is doubt it is best to use a PH neutral cleaner, that way you don’t risk eating off that coating (like I did when I was 18).

Nickel Safe Cleaners

Many Ice machines have nickel or tin plating on the evaporator. USe the wrong cleaner and you can permanently damage the evaporator. When cleaning an ice machine, use specifically designed nickel safe cleaners to ensure you don’t end up with a mess on your hands.

Be reasonable 

I see many guys use cleaners when a cleaner just isn’t required. You don’t need to use concentrated chemicals every time you rinse a coil, you don’t need to pump a quart of the brown stuff on your truck in the drain pan on every PM. Clean until its clean, but sometimes a rag or a soft bristle brush or a shop vac will do the job better than coating everything in layer of nasty chemicals.

Do a good cleaning… Just pay attention.

— Bryan


Please Note: There have been some legitimate questions about a few of the points in this article and in the diagrams. While Justin Skinner is an experienced tech and totally qualified to write this article we are going to be specifically looking into the question of the best location of the circulator pump as well as addressing “point of no pressure difference”. This article is still full of very useful points so it will remain up until we can research and potentially make a few changes. It is also worth noting that Dan Holohan’s book “pumping away” is considered the authority on the subject in addition to his website Thanks!

This article is the third in a series by senior boiler tech Justin Skinner. Thanks Justin!

Boiler piping is a much-debated topic in the HVAC trade. In fact, many books have been written on the subject. Should the circulator pump be on the supply or return? Where should the expansion tank be located? The best way to bleed radiators? If you talk to 10 different technicians, it is very possible to get ten different answers. And the short answer is, they are all correct. Because there is no “one size fits all” approach to boiler piping and layout. What works on one boiler system may not on another, and when a new boiler is installed on an existing system, there are plenty of potential issues which could be unique to that specific set up. Water is weird, sometimes. Like air, water doesn’t always do what you engineer it to do. I couldn’t count the times that I’ve been involved with projects with issues that left engineers scratching their heads because how they designed the water to flow through a system vs. what the water is doing is completely different. A technician need to be able to identify and correct what causes flow and heat exchange issues when we find them, and to do that, we need to know how it’s supposed to work.


Hot water piping



Here is a basic drawing of a hot water boiler system. This is an optimal setup, in my opinion. I like to feed water into the supply side before the expansion tank. Typically this area is the lower pressure which allows feeding easier. A lot of the air should go to the expansion tank, and the rest will go out into the system, which is ok because if it is in the system, it can be bled as long as there are bleed valves. Also, it allows the cold feed water to heat up before it enters the boiler, avoiding shock. I prefer to put the circulator pump on the return side, as well. I’ve had better luck with flow and pump life when the pump is pulling from the system, rather than pushing into the system. Gravity and convection play a part as well. Hot water naturally wants to rise, and this natural circulation helps the return side pump move water much easier than if the pump were on the supply side of the same system. If a pump must be installed on the supply side, I prefer to install it after the expansion tank. Also, as indicated by all of the X’s, install shut off valves wherever you can. It will save you a ton of time and hassle later on when a repair is required.


This is all my opinion, and is based on my personal experiences. However, if someone calls and asks me a boiler piping question, my first suggestion is to do whatever the manufacturer recommends. Most boiler installation literature shows diagrams on piping set up, and that is the baseline for installing a new boiler, and possibly diagnosing a flow issue. Some manufacturers show the circulator on the supply, some on the return, and some don’t care either way. If you follow the manufactures specs, to the tee, 99% of the time you won’t have a ton of issues with flow and boiler operation.


Bleeding air from systems is necessary from time to time. Some boiler systems are much easier to bleed if they are piped to allow air to be removed by automatic vents or go to radiators to be bled. On system drain down and refill, I will typically bleed air after filling the system, while it is still cold and no pumps are on. After that initial bleed, I turn the boiler and the pumps on and allow the boiler to heat up to operating temperature. Once it is hot, I shut everything off, boiler and pumps. This allows the air that may be traveling with the water to go up, either to higher radiators or bleed points. I bleed air, turn everything on again, turn it off, and repeat until all the air is out.


A lot of older boilers guys I have worked with only bleed air with the pumps running. I could never get a satisfactory answer as to why, and I have had much better luck bleeding air from a system with the pumps off. If you do things differently, and it works for you, that’s great. Again, most of this is my opinion based on my experiences, and there is more than one way to skin a cat. Also, increasing boiler system pressure while bleeding helps speed things up. Most automatic water feed valves are factory set to keep the pressure at 12 psi, which is a pretty standard pressure. If your system is 12- 15 psi, bumping it up to 20-25 psi will help speed up the bleeding process. Always make sure you aren’t exceeding the pressure rating of the relief valve if you increase system pressure to bleed. And don’t forget to bleed excess pressure off after you have completed.


Steam Piping :

A basic steam system is much simpler than a hot water system. The natural rising of the steam allows it to move through the system, so there is no need for a circulator pump to move steam. Steam is a vapor, so there is also no need to bleed air, and no need for an expansion tank on a basic steam system. However, piping pitch is much more crucial to this system. The piping must have pitch or fall to help the steam rise, and more importantly, to allow the condensate to flow back to the boiler. Level piping holds water, so it must have fallen. Also, a Hartford Loop is required to connect the supply and return. This is basically an equalizer to balance the pressure between the two sides of the system. Also, as part of the loop, the condensate return line connects 2’’ below the water level of the boiler. The loop is used to prevent water from leaving the boiler through the return if the pressure is lower than the supply, or if there were to be a leak on the return. This piping configuration was mandated by code for a long time as a prevention for low water conditions causing the boiler to dry fire. With the invention of more advanced low water protection devices, it isn’t required by code everywhere but still is a good idea. It allows added protection if the low water safeties were to fail.


Steam traps are integral to steam systems as well. A steam trap is a check/float valve that allows condensate to pass through and return to boiler while preventing steam from passing. Steam traps are locating on the return (outlet) side of steam heat exchangers, radiators, etc. The goal is to keep the steam in the radiator as long as needed for it condenses to liquid water, thereby releasing as much heat to the radiator as possible. Without steam traps, the steam would blow right through the radiator, and would not stay there long enough to properly heat it up.

                   Steam Trap


There are an infinite amount of piping configurations that you will run into of the course of a career, some much better than others. And certain situations dictate changes and configurations that may allow one system to work well, and the same configurations could cause a different system to function poorly. In short, every system is different, and a lot of times I am required to think outside of the box to make a poorly designed system work. But as mentioned at the beginning, if you have a basic understanding of how things are supposed to work, it makes diagnosing why it isn’t working a lot easier.


–Justin Skinner


This article is written by Senior Boiler Tech Justin Skinner. Thanks, Justin.


Oil burner nozzles are present in most forced combustion air burners. They are used, with an oil pump, to atomize fuel oil and allow it to burn. Atomizing is raising the pressure of the fuel and forcing it through the nozzle. The fuel comes out of the nozzle essentially vaporized. It is then mixed with air and burned. Nozzles are also used to meter the amount of fuel being used, and to vaporize the fuel in an efficient pattern suited to the burner chamber of whatever equipment it is installed on. If you work on burners, you have probably seen and changed out your fair share, as periodic nozzle replacement is necessary for clean and reliable burner operation. But there is more to nozzles than what meets the eye. Let’s take a closer look.

     The numbers on the nozzle tell us the specific rating of the nozzle, the spray pattern angle, and the spray pattern type. The nozzle listing here has a .75 GPM rating. That means the nozzle will spray .75 gallons per hour of fuel oil at 100 psi. Nozzles are generally rated at 100 psi, and that is the pressure that most residential style oil burners run at, but not all.  It also has an 80-degree spray angle. That is the angle at which the spray comes out of the nozzle. The smaller the angle, the more narrow the spray pattern. Think of a garden hose with a spray nozzle. If you squeeze the handle only a little, the spray comes out at a wider angle. This would be similar to a higher degree spray angle. As you squeeze the handle more, the outer edges of the water get closer together. A closer spray pattern would be a smaller angle. Larger spray angles are generally used for wider, shorter burner chambers, and smaller spray angles are used for narrower, shorter chambers.


The letter on the nozzle indicates the spray pattern. Different manufacturers use different letters for the same patterns, so we will use Delavan as the example, as it is the most common nozzle manufacturer I use. Patterns are designated as solid (B), hollow (A), and semi-solid (W). A solid nozzle indicates the vaporized oil is distributed evenly throughout the entire spray pattern. A hollow nozzle distributes more of the oil to the outer ring of the pattern, and a semi-solid is neither. W nozzles are typically considered a replacement for both A and B nozzles, although that is not also the best option. I prefer to replace nozzles with the type and pattern specified by the manufacturer, but late nights and on-call situations do not always allow it. Typically the nozzle is designed to fit the equipment and not the other way around, so using the correct nozzle can save you a lot of headaches and a sooty mess.


The pictures above show an exploded nozzle. The back portion is a very small particle filter. It is composed of thousands of bronze pellets fused together. This filter is easily clogged by gunk, so an in-line filter should be used to catch most of the fuel sludge and trash before it gets to the burner. After the filter, a slotted distributor is present. The pressure of the fuel from the pump causes the distributor to spin, and the oil increases velocity inside of the nozzle. The oil is forced through the head of the nozzle, which contains a small hole/tube. The sudden decrease from high velocity/pressure to atmospheric pressure through the tube causes the fuel to vaporize. Once the vaporized fuel leaves the nozzle, it is mixed with air at the burner head and is ignited if the fuel/air ratio is correct and the ignition source is strong enough. Nozzles are rebuildable if you need to in a pinch. But they are finely machined to exacting specs, and fairly inexpensive. So I would only try to rebuild a nozzle in an emergency situation.


Nozzle flow is rated in GPH @ 100 psi pressure. One gallon of #2 fuel oil contains approximately 140,000 (give or take a 1000 or 2). So a 1 GPM nozzle @ 100 psi is a 140,000 BTU burner input. If the burner efficiency is 80%, that means 20% of the fuel energy goes up the flue as unused energy. So a  1 GPM nozzle on an 80 % efficient burner is equal to around 112,000 BTU’s available from the fuel. But what if you need a 1 GPM nozzle, but you only have a .75 GPM nozzle available? Well, increasing the pump pressure above 100 psi can allow for the same amount of fuel input with a smaller nozzle.


As the chart above shows, the same nozzle flow rate can be achieved with a variety of nozzle GPM sizes and pump pressures. It’s not advised to change nozzle size or pump pressure during an inspection unless there are issues. It’s more to get you by until you can get back with the correct nozzle. Also, if you change the nozzle size or pump pressure outside of what the manufacturer recommends, make sure you note it on the equipment for the next tech who may go behind you. It’s also an option to downsize the nozzle GPM and increase the pump pressure for hard/smoky light-offs and shut downs. The higher velocity from the increased pump pressure allows for the complete vaporization of the fuel. This allows for a cleaner light off, cycle, and shut down.

–Justin Skinner

This article was written by senior furnace tech Benoît (Ben) Mongeau. Ben hails from the frozen tundra of Ontario, Canada where high efficiency gas furnaces are commonplace.

While some codes and practices may be different from the US I find that most of it is common sense and translates pretty well. One glaring difference between Canada and the USA is the requirement in Canada for specifically certified PVC or CPVC vent pipe. Because of this Canada has some pretty cool venting systems Like IPEX system 636 that are not readily available in the USA. I’m leaving all this in because there is already talk about making the change in the US so I bet it’s coming.

Venting for High efficiency Gas Furnaces –  Assembly

Here are some good venting practices.  (This is mostly stuff I learned during a training session from IPEX, one of the major manufacturers of plastic piping, with a little of my personal experience and tips)

First of all, venting must be planned in order to be sized properly.  Depending on the BTU rating, length, number of elbows in the run, the size will vary, typically in residential from 1½ to 3-inch pipe.  Every manufacturer has its own vent sizing charts.  Read the manual, don’t guesstimate.

Use the proper tools when installing plastic venting.  !!!Avoid using a sawzall or hacksaw to cut your lengths!!!: it creates a multitude of statically charged shavings that will stick to the inside wall of your pipe.  Once that condensate starts flowing, it will bring all those shavings to your drain and trap, blocking all those narrow passages and causing water backups, furnace failures, all kinds of things to piss off your service colleague who’s on call that night.  I highly recommend using a proper pipe cutter.  It is the best way to achieve a clean, straight cut.  The straighter and neater the cut, the more joining surface you have once you’re cementing it together.

vent pipe cutter and chamfer/deburring tool (REED venting solutions kit, which I highly recommend purchasing 

It is recommended to dry-fit the whole vent system before actually starting to cement joints together, just to be sure your lengths and angles are good.  Also, as mentioned in my condensate drainage tip, make sure the vent is sloped towards the furnace for the whole length.

Before applying cement, prepare the pipe ends by cleaning them up (wipe off any obvious dirt) and, most importantly, reaming them.  Use a proper reamer / chamfer tool (pictured with the cutter above).  This is a crucial step: if the pipe end is not reamed/deburred, the edge actually tends to slightly stick outwards, especially when cut with a proper cutter, ironically.  This will cause the pipe to push (I like to call it ‘’snow plowing’’) the cement at the bottom of the joint instead of letting it slip around the pipe, leaving large uncemented gaps in the structure of the joint and often causing leaks.  See comparative pictures of chamfer/un-chamfered pipe ends below.


Cut, not reamed /chamfered 636 PVC pipe


The same pipe end, reamed / chamfered and deburred  

Next, once all pipe ends are reamed and clean and ready for assembly, it’s time to start cementing.  Apply primer first if required, then apply the cement.  Don’t be shy, apply a generous coating around the whole joint surface of the pipe and fitting (yes, cement is applied on both the pipe and the fitting).  I recommend going around the pipe/fitting 3-4 times with the dabber/roller/brush to ensure a full coating.  Once both ends have cement applied, quickly (before it dries!) push them together, straight and all the way to the bottom of the joint, and as much as possible try to give the fitting a quarter-turn while assembling the joint to further evenly coat the entirety of the joining surface.  Very important: once you hit the bottom of the joint, hold the pressure for about 30 seconds (or longer) so the cement has time to set!  If you let go immediately, the still wet fitting and pipe will naturally pull back from each other and this can easily lead to leaks.  Wipe off any excess/runoff cement if necessary and proceed to the next joint.

Once assembled and when the cement has dried, as I mentioned before, the two pieces are basically welded together.  You cannot take them apart, so make sure your angles are correct, or you’ll have to cut it out and restart.

Support the pipe as necessary, per local codes/guidelines.  Support spacing usually varies depending on pipe size.  Avoid creating too much tension on the venting as it can lead to leaks/cracks.


Other tips:

  • Don’t leave your cement cans open longer than necessary.  The solvent part of the cement is quite volatile (evaporates easily) and as it evaporates, the viscosity of the cement will increase and it will get more difficult to use.  Once your cement has gelled (i.e. has a consistency very reminiscent of that of Jell-O) throw it out.  It is no good.  Keep an eye on your cement’s viscosity.  It should always be liquid, although with various degrees of thickness depending on the type, but NEVER jelly.
  • If a reducing fitting is used on your venting, always install it on a vertical portion, never horizontal, otherwise it will allow for condensate to pool in the vent.  Remember… slope for drainage!
  • Respect local guides and regulations and manufacturer’s specs regarding clearances when choosing where to terminate the venting outside.  Also, terminate the exhaust higher than the air intake (usually about 1ft minimum) if you are installing a sealed combustion system, to avoid recirculation of combustion products which can be quite disastrous.  Typically on a sidewall termination the air intake will be terminated with a downward-facing elbow and the exhaust will be snorkeled up, i.e. elbow up, 1ft pipe, then elbow out away from the wall.  There are also manufactured termination kits (concentric, for example) that are available and sometimes easier on the eye.  Make sure it’s certified, though!  Again, manuals will tell you if there are termination kits available and certified for use with the product.
  • Be careful to read install manuals for any specifics regarding the furnace you are installing.  There is often specific procedures for attaching the vent pipe to the cabinet’s internal exhaust fitting/flue collar etc. and it will vary from one manufacturer to the other.

— Ben

You can read the full IPEX 636 install instructions HERE

This article was written by senior furnace tech Benoît (Ben) Mongeau. Ben hails from the frozen tundra of Ontario, Canada where high efficiency gas furnaces are commonplace.

While some codes and practices may be different from the US I find that most of it is common sense and translates pretty well. One glaring difference between Canada and the USA is the requirement in Canada for specifically certified PVC or CPVC vent pipe. Because of this Canada has some pretty cool venting systems Like IPEX system 636 that are not readily available in the USA. I’m leaving all this in because there is already talk about making the change in the US so I bet it’s coming.

Venting for high-efficiency gas furnaces – Materials

Due to the condensing nature of a high-efficiency furnace, its venting must be made of a material that is resistant to corrosion. In a great majority of cases, plastic piping is used to vent high-efficiency equipment. It is classified as “Type BH” venting. The lower temperature of the exhaust gases also mean that the natural draft effect observed in conventional metal chimneys (heat rises) does not occur at a significant level. Which means those exhaust gases have to be forced outside. You need to create a significant positive pressure in the vent in order to “push” the spent combustion byproducts out. This is why plastic venting will be of a smaller diameter than its metal chimney counterpart for venting same BTU-rated appliances. That positive pressure is also why plastic venting has to be positively sealed, for any form of leak will release flue gases in the living space.

There exist many, but mainly three types of plastic are commonly used for high-efficiency appliance venting: ABS, PVC, CPVC.

(Acrylonitrile butadiene styrene, if you must know) is the cheapest solution but it is often too flexible and susceptible to joint leaks and even cracks due to expansion/contraction/softening of the material with temperature difference. Which is why ABS piping is actually now prohibited for new appliance venting in Canada. Never use primer on ABS.

(polyvinyl chloride) is what is most commonly used nowadays. There are different types/grades of PVC on the market and some of them may not be allowed for use as flue gas exhaust. Always check your local/state/province codes and regulations. For example, here in Canada Schedule 40 PVC DWV (drain PVC) may not be used. Only FGV (flue gas vent) PVC certified to a specific standard (ULC S636) may be used.

Note from Bryan: In the USA schedule 40 DWV pipe (the usual stuff) is still the standard, there is talk this may change soon so stay tuned.

(Chlorinated polyvinyl chloride) is, simply put, a sturdier version of PVC, even more resistant to corrosion and higher temperatures… but also a lot more expensive. It is more often seen on high-efficiency residential boilers, where, in some applications, even PVC is not sufficiently resistant. For easy recognition, vent/drain piping is usually color coded. Most often, ABS is black, PVC is white and CPVC is gray / tan. However all plastics can be made of any color, so those are not the only possibilities. Be extra careful about that especially when it comes to certain fittings supplied with the furnace. A prime example would be the vent flange on new Carrier/Bryant/Payne furnaces. It is black, but actually is made of CPVC. Which means you may not use ABS (or PVC) cement to attach it to your venting.

Note From Bryan: Read the manufacturer’s instructions

Those plastic piping systems are joined with a cement, which most people will incorrectly call glue (it’s okay, I usually say glue too). It is not glue. It is not an adhesive. Cement is basically the plastic you are working with, dissolved in a solvent. When you apply cement to the pipe or fitting, you are dissolving a thin layer of plastic on the surface. Once the joint is assembled, the solvent part of the cement evaporates, leaving only a continuous piece of plastic that is now basically part of the pipe and part of the fitting. The two pieces become as one (how poetic!). They are basically welded together. Always be careful to use the adequate cement. PVC cement will not bond properly to ABS or CPVC. An exception I know of would be the IPEX System 636 CPVC cement, which is certified for joining both PVC and CPVC pipes in any manner (PVC to PVC, PVC to CPVC, CPVC to CPVC) . Always use the correct cement, made by the same manufacturer as the pipe you are installing, since it uses the exact same plastic “recipe”, if you will. It is the only way to ensure a proper bonding (again, in Canada they utilize certified systems).

In addition to the cement, there is also primer, which is nearly pure solvent. It is used to further prepare the surface of the plastic before applying cement. Note: In practice it not necessary to always use primer on DWV pipe (UNLESS IF SPECIFIED BY YOUR LOCAL CODES). Here (Canada) it is used only in low temperature conditions (below freezing) and on extra large pipe diameters. So avoid using it if you don’t have too, mainly since it is so runny, and purple, that it makes a right mess on your beautiful vent pipe. Also, CPVC and ABS do not require a primer (according to Oatey)

As always, READ the manufactures instructions on the furnace / boiler being installed as well as the pipe / cement being used to ensure that you are using the correct
materials for the job. In part 2 we will cover more specific vent fitting tips.

— Ben

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