Month: January 2017

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


Because some have expressed confusion, this article pertains to refrigeration systems that have a Receiver.


I frequently see techs online struggling with charging or troubleshooting refrigeration equipment and using subcooling as a diagnostic or charging method. Please don’t do this unless you understand it fully . Many times, trying to charge a refrigeration system to a specific subcooling value is going to result in a serious overcharge.




Glad you asked.. First, let’s take a look at a simple system and focus on the condenser, liquid line and metering device. As we condense refrigerant and fill the liquid line and condenser, the metering device begins restricts flow somewhat liquid to back up into the condenser. This ‘stacking’ effect as it’s commonly called, allows more time for the liquid to be in the condenser and to reject heat. That heat rejection is what results in additional subcooling. Adding more gas to this system will simply result in more liquid being stored in the condenser, more heat rejection from that liquid and, consequently an increasing subcooling value. That’s the system that you understand and that subcooling can be effectively used as a diagnostic and charging metric.


Now, let’s put a receiver in the system between the condenser and the metering device. Ok, we’ve got liquid in the condenser and it enters the receiver before the metering device. As the liquid line fills and the metering device starts to restrict as before, where does the liquid wind up? The receiver. It doesn’t wind up in the condenser where heat can be rejected, but rather in a tank to be stored. Now, if you’re measuring subcooling, before OR AFTER the receiver, you’re not going to see a significant change in that value before or after we reach a proper charge.


If you continue to add gas to the system it’s going to continue to fill the receiver until that liquid backs up to the inlet port of the receiver. Now, you’re seriously overcharged because a receiver shouldn’t be more than 80% full, but the system can now back liquid up into the condenser and allow for the subcooling to increase as it did in the simple system we looked at
first. This is why, when you have a receiver, you need to use either a sightglass or some form of receiver level monitoring to determine if you’re charge is correct and not just use subcooling.


— Jeremy Smith

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

When you start talking airflow, it can get pretty in-depth pretty quick. There is a big gap between what is useful for the average tech to apply every day and the whole story so let’s start with the simplest part to understand, Static Pressure.

Static pressure is simply the force exerted in all directions within any contained substance, or in this case air. This means it’s not the directional force of air moving or blowing (that is called velocity pressure), it is simply to force pushing out on the positive side of the air system and pulling in on the negative side.

Measuring static pressure helps a tech know whether or not the system has excessive resistance to air flow overall or at a particular point.

Static pressure is measured in inches of water column (“WC) and is the amount of pressure needed to displace one inch of water in a water manometer.


A Magnehelic is a brand name for a high-quality Dwyer analog pressure gauge that comes in many different scales. Many techs will already have a high-quality digital differential manometer (like the Testo 510) for reading gas pressure, which makes getting a separate Magnehelic largely unnecessary.

When using a manometer or a Magnehelic, you will first zero it out to room pressure (for a Magnehelic make sure it is level). Next place the negative side probe in the return side of the unit after the filter but before the blower and place the positive probe in the supply duct. Keep the negative side probe away from the side of the blower and insert the probes in as straight and square as possible. It is advised to use a static pressure tip like the one shown below to prevent air velocity pressure or air currents from interfering with the static pressure reading.

With a static pressure tip point the tip against the direction of airflow (points opposite the airflow) in both the return and supply. DO NOT confuse a static pressure tip with a pitot tube tip. A pitot tube tip is designed to measure velocity pressure or total pressure (velocity + static = total)  NOT static pressure, and it will have an open end.

Total external static pressure is return plus supply, positive plus negative and in general, you would like to see it be 0.5″ or less…

If you see 0.9″ or higher that is when you start to see trouble on most residential systems, but as always, each piece of equipment is different depending mostly on motor design. Whenever possible design your equipment / duct system so the result is 0.4″ – 0.6″ of total static (Once again talking general residential / light commercial here).

If you do find it to be high, then read the return and supply separately to see which is higher which is just a matter of removing the hoses to your manometer or Magnehelic alternately. Whichever reads higher is the greater cause of the issue.

I could keep going on this, but instead, I will just link to some more in-depth articles if you want to do more reading.

— Bryan

Epic airflow write up from Dwyer 

Measuring Airflow from TruTech

Troubleshooting Ductwork by ACHR News



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

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

Steam plays a very important part in all of our lives, whether we know it or not. Virtually every article of clothing and accessory you are wearing right now relied on steam for either manufacturing or packaging. Hospitals use large steam boilers for dehumidification, sterilizing medical equipment, and plenty of regular old space heating and domestic hot water through heat exchangers. The power entering my house is generated by a high pressure steam boiler a few miles away. Here are some common components used to operated steam boilers safely and efficiently.

Operating/High Limit Controls:

The operating control shown here is made by Honeywell, and it is the most common that I run into. It is basically a normally open/ normally closed set of contacts with 1 common feeding both. There are 3 terminals : R, W, and B. R is common. The switch through R to B opens on a rise in pressure, and the switch between R and W closes on a rise in pressure.

Typical wiring is done through the R to B circuit, breaking the control voltage going to the burner that calls for it to start.  The pressure is set by the user. There are 2 scales to be set on this control. The first is the pressure at which R and B open, and the second is a subtractive differential in which the switch closes.

Lets say you have your first scale, the cut off pressure set at 10, and the second scale set at 3. That means the R to B switch will open at 10, shutting off the burner. It will close at 7 (10-3=7), indicating a pressure drop and enabling the burner to run. If you change the second subtractive scale to 5, it will close the switch at 5 (10-5=5). The high limit shown is a normally closed switch with a manual reset that opens on a pressure rise. This control will not reset itself should the pressure get high enough to open its switch. This is a safety device that should never be bypassed, and if one is tripping and needs to be reset, more investigation is required to determine the cause.

Modulation Control

The mod control is used to increase or decrease the firing rate of the burner. These controls aren’t typically seen on smaller single or 2 stage burners, but in larger burners that require different burner firing rates depending on steam load and requirements. They contain the same terminals as the operating control listed above ( R,W, and B), but act completely different.

The mod control pictured is not a typical open/closed switch, but rather a potentiometer that changes in resistance with a change in pressure. Basically, as the pressure rises, resistance is decreased between R and W, which causes a connected modulation motor to drive shut, and drive the burner to a lower firing rate. Similarly,  when the pressure falls, resistance is decreased between R and B, which drives the mod motor open, increasing the firing rate. There are mod controls that are normally open/closed switches, and they look identical to the one pictured above. If you look at the inside cover, you can usually find a diagram that shows operation, or a part number to be able to look it up. Below is a typical modulation motor. This motor is connected to air and fuel dampers and valves, adding or taking away both to the flame in unison based on the steam load and input from the modulation controller.

Condensate/Deaerator Tank

In a steam system, superheated water (steam) is sent out to the piping system. As the steam cools, it condenses in liquid water. This water is collected in a tank and reused to feed the boiler. There are a few reason for this. The most important reason is safety.

When a boiler gets up to temperature and is making steam, there is a optimal water level in the boiler where below is water and above is steam, almost like a accumulator on a heat pump system. At atmospheric pressure, water boils at 212 degrees F. In a pressurized steam system, that temperature is higher, as thermodynamic laws require. Increase pressure, increase boiling (vaporizing) temperature. So the liquid water in the lower portion of the boiler is above 212 degrees when steam is being produced. If cold water is introduced to this environment, it rapidly (and potentially violently) expands. Water expands 1,700 times when it is converted to steam. We collect the condensate, which hopefully is still hot, and feed it to the boiler because hot water does not flash to steam as easily as cold water. It is safer and easier on the boiler vessel to use pre heated water to make steam. Cold water going to a hot boiler can be loud and pretty scary. It bangs and pops and the boiler can move some. Optimally, the water being fed from the tank should be as close to the boiling temperature as possible. Also, water heated in the feed tank releases oxygen molecules from the feed water, which is important for preventing corrosion and scale build up in the boiler. Less oxygen in the boiler, the less rust. Its common to run steam to a feed tank to ensure the feed water is sufficiently heated. Water treatment chemicals are often added to the feed tank, and pumped to the boiler by way of the feed water to inhibit rust and corrosion. And of course, reusing water is a cost saver for the customer. It’s more expensive to treat and heat fresh water than it is to reuse pretreated and already hot water. Below is a typical condensate tank.

Water Level Controls

Water level is important in steam boilers, and they aren’t completely full. There a level at which the internal components are sufficiently covered in water, and there is room for the water to boil off above. There are many types of level controls, the most common for larger boilers being shown below. Made by mcdonnell-miller, this is a float type controller with a series of normally open and normally closed switches. The switches control the feed pump that feeds the boiler from the condensate tank, and can be configured to shut off the boiler if the boiler water level gets too low, too high, and can activate an alarm circuit. Smaller steam boilers require a similar device, and there are many varieties out on the market. These controls are crucial in the safe operation of a steam boiler. If the water level drops and the boiler dry fires, bad things happen. A quick google search of serious boiler explosions will indicate in the reports that bypassing or jumping out the switches on these devices are the most common cause. If you don’t know how its supposed to work and are not pretty familiar with the device, the last thing you should do is mess with it. Call a senior guy or tech support or someone. Boilers do explode, dont be the cause of it. There are probe type water level safeties as well. They use power to detect conductivity from the probe through the water. If the water level drops, no conductivity is detected and the boiler should shut down. Level controls and safeties should be inspected and tested, and if they fail they should be repaired or replaced immediately.

Float type level controller and sight glass

Level switches inside float head


Sight Glass

The sight glass is a real time view into the boiler water level, and a quick indicator that all the feed water controls are in working order. I am in the habit of looking at the sight glass before anything else when i come into a boiler room, and constantly checking it while I am working in there. As stated above, boilers in low water conditions can be catastrophic, so it’s crucial to pay attention to. If you come across a boiler with no water in the sight glass and you don’t know what to check or why, the best thing is to turn the burner switch off, get the heck out of there, and call for back up. The last thing you should do is start turning on pumps and opening valves to try to fill a hot boiler that is under pressure. Your personal safety is much more important than getting the boiler up and running.

Steam boilers can be dangerous if not properly serviced and maintained. I’ve run into situations that were pretty intense before, and had to call for help many times. It’s tough for a lot of techs to admit they dont know something and they need help (me included), and it’s especially tough when the boss is telling you to just get it done. But safety and getting home to your family is the most important thing we will do today. And if you are in a uncomfortable situation with a larger steam boiler, asking for help may mean the difference between going home or not. There are plenty of other components involved with steam boilers, but this is a basic overview. By reader request, the next article will cover basic boiler piping systems. If there is something that you would like clarification on, or a topic i did not cover, feel free to email or message me or comment below.

–Justin Skinner

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