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Heat Exchanger Training Lab

Heat Exchanger Lab

Hi, my name is Steve Holland. I consider myself a heat exchanger geek, guru and a heat exchanger expert. For the past 29 years, I have dismantled, repaired and re-build thousands of furnaces. I’ve come to find enjoyment in teaching other companies or technicians on how to become experts or gurus in heat exchangers and furnace safety. If your company is seeking heat exchanger training and certification, Rapidtech may be the perfect for you!

It’s 100% online

It’s 100% a true certification

All graduates will receive a diploma or course completion certificate, shoulder patch and laminated card to show customers.

Today, we offer an online portal that offers a full Heat Exchanger Certification. What makes our certification a great fit for many companies?

  1. It’s affordable
  2. No down time for techs
  3. Self paced learning
  4. You’ll get access to all of our videos that show where to find failures
  5. It works!

Each class comes with a supporting document, video and a quiz. Once the entire course is complete your student can print out their certificate of completion.

Want to learn more: email me at:

Click here to view FREE resources and heat exchanger training


Steve Holland


Quite the Cracked Heat Exchanger! Arcoaire Model GUH


Each week, I take a detectives deep dive into furnaces, boilers and air conditioners as part of my role at Rapidtech. My hobbies are a little different than most with one being that I get all lathered up when I get the opportunity to break down HVAC equipment for the purpose of developing technicians and finding problems. Our goal is to “Change the HVAC Industry One Tech at a Time”. It’s also our goal to help homeowners remain safe, live comfortable and avoid unnecessary expensive repair bills. In this video, you will discover what I discovered with Snyder General’s Arcoaire Model GUH.



Rapidtech Course – Lennox Cracked Heat Exchanger

In 1990, when I started as a service technician, I had the privilege of working on literally thousands of these Lennox Gas Furnaces. If you are a technician this is a must see video on where these Lennox curved heat exchangers fail.

Remember to always check the following when and if you find a failed heat exchanger on a Lennox furnace or any other furnace with a cracked heat exchanger.

  • Static Duct Pressure
  • Filter size
  • Evaporator coil
  • Number of supplies and returns
  • Gas Pressure
  • Delta T
  • Venting
  • Draft
  • Perform a combustion analysis
  • Check for gas leaks


Furnace Destroyer #3 – The Filter

Heat Exchanger Destroyer #3

By: Steve Holland


The dirty or clogged air filter.

End of blog. Jk


Alright, I’ll give you some helpful information. The dirty air filter is the one of the three main causes of no heat calls and no cooling calls across the United States. The filter is designed to keep dirt and debris from entering the mechanical components of your heating and cooling system.

On a normal cycle, your air conditioner will move 400 cubic feet of air per minute through the furnace. On a heating cycle this number is slightly less and will vary if you have a variable speed blower. Regardless, this is a whole lot of wind! All of this air contains dust that will eventually plug the surface of the air filter.

Once you start restricting air flow the furnaces heat exchanger will see higher temperatures resulting in failure. The blower in your furnace is designed to serve two purposes:

  1. Transfer the heated energy from the furnace to the home via the duct system
  2. Sub cool the heat exchanger so that the furnace does not overheat

Here is the simplest way to understand how a filter will destroy a furnace.

By design, the furnace or air handler will have a certain engineered air flow requirement. When you restrict the air flow, you also allow higher temperature and heat stress to develop in areas of the heat exchanger. This continued stress will destroy a furnace.

Dirty or plugged filters cause the following problems:

  1. Higher utility bill. Drive your car around with your foot on the brake and see if your fuel economy drops. The same is true with your blower motor and furnace. If the furnace can’t move the right amount of air, as a result of a restricted air filter, the unit will simply draw more gas and electricity.
  2. Comfort is reduced.
  3. Extra wear and tear and additional stress to your system
  4. Crack the heat exchanger or cause excess temperature stress
  5. It can cause a no heat or no cooling
  6. Your air conditioning coil could freeze and cause damage to the furnace or air handler
  7. Poor airflow to parts of the building




  1. Plan to check your filter monthly. Some filters will last up to 12 months. I suggest you always are safe than sorry and replace the filter on routine rather than wait for it to plug up.
  2. There is nothing wrong with a 1” filter, provided that the pressure drop across the coil is within range for that air handler or furnace.
  3. The 4” media air filter is a much better choice than a 1”. However, this will cost more at the time of installation.
  4. I suggest that you purchase a minimum of a MERV 10 filter. In most cases, I suggest a MERV 12 or higher. Be careful – some stores offer a filter that is manufactured by a leading brand that is extremely restrictive in air flow. I can’t say their name(s) or they will sue me.
  5. Avoid the cheap filters. They do nothing but keep beach balls from entering your furnace.
  6. Post filter contamination can be a problem. This is the area where you slide the filter into the slot. If there’s a gap – often times the filter will miss much of the debris. I suggest this gets sealed with a magnet or filter cover.

The bottom line is that if you neglect your furnaces’ air filter – you will pay for it. Chances are that you will need to replace your furnace or air conditioner sooner than normal or you will ruin major parts.

Get in the habit of changing your filter. Use your smart phone’s calendar or reminder system. With the technology available today there’s no excuse for neglecting the air filter.

In a few weeks I will share Heat Exchanger Destroyer #4 – The dirty air conditioning coil (evaporator coil)




Furnace Destroyer #2 – Poorly sized ducting

Heat Exchanger Destroyer #2  - The undersized duct system

Duck’s don’t whistle – they quack! Do your ducts whistle? The problem can be easily identified, corrected and resolved. All you need is an educated technician, an honest HVAC company and few good test instruments.

In my last article, I spoke of heat exchanger destroyer #1 – The Design Factors. In this article, I will share what I know about an undersized duct system.

Perhaps you have a furnace that has a cracked heat exchanger, or requires a pre-mature replacement. Let’s assume that you ruled out the manufacturers design. As an HVAC investigator, I want to know what is going on. The first place I look is at the size of the air conditioning system and Btu output of the furnace. Once I know these numbers, I can calculate what the required air flow requirement is for that system. Let’s assume that the furnace is sized correctly.

Let’s do the math.

In the air movement world, an air handler or furnace must provide 400 cfm (cubic feet air per minute) per ton of cooling. A ton of cooling is equal to 12,000 Btu’s (British thermal unit) of heat transfer or in simple terms 12,000 Btu’s of heat removal. Understand, in the cooling mode we remove heat and in the heating mode we transfer energy thus providing heat.

If you have a 3 ton cooling system that means that you should be moving a minimum of 1200 cfm across the evaporator coil. This also means that the duct system’s combined design capacity must also move 1200 cfm through the duct system and to all of your supply registers. Guess what? The return system must also provide enough return air so that the air handler or furnace can provide the correct air flow.

Think of this – how easy would it be to fill a swimming pool with a straw? How difficult is it for your heart to deliver oxygen and blood through a body with clogged arteries and veins? It’s no different with an undersized duct system. Bigger is not always better. Do not make the assumption that with giant ductwork the problem will be resolved. This is another issue that I may write about in the future. The duct system must be able to deliver the correct amount of air flow. Just like your heart must deliver the correct amount of blood and oxygen.

What do you suppose will happen if you are moving 1000 cfm on a system that requires 1200?

If you have too small of a duct system there’s a good chance that your registers will whistle and your system will be noisy. There’s also a guarantee that you will destroy a furnace or heat exchanger.

I know that I mentioned air conditioning and cooling, but what about the furnace and heat exchanger? The general rule is that if you have the proper airflow for the cooling mode, there’s a probable chance that you will also have enough airflow for the heating mode.

I recommend that duct systems be sized at .08 of static duct pressure with a 400 cfm air movement requirement. These are general numbers. In the commercial world, these numbers may not work. The best policy is to look at the manufacturers’ or engineers specifications and go with what they recommend.

Regardless, an undersized duct system will destroy a heat exchanger and it could result in one or more of the following problems.

  • Poor airflow to certain rooms in the home
  • Higher utility bills
  • Pre-mature failure of compressors
  • Pre-mature failure of blower motors and other furnace components
  • Loss of comfort
  • Whistling ducts – or, a noisy system
  • Freeze up a coil and cause water damage to the furnace or air handler
  • For those in the south – water leakage through the ceiling

The list goes on and on. Every technician must be privileged to properly trained on how to test, read and communicate static duct pressures. I also believe that each and every tech must learn how to calculate cfm requirements. All of this can be completed and addressed by training and educating technicians.

Watch for my next blog post on Heat Exchanger Destroyer #3 – The dirty or plugged filter.

Homeowners: Hire the right HVAC Company – many problems will be prevented.

Contractors: Invest in your people and hold them accountable – many problems will be prevented.


“Changing the HVAC industry, one technician at a time”

Steve Holland


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 Steve Holland is a national advocate for the skilled trades and also the owner of Mr. Holland's Heating and Air Conditioning in Wisconsin. If you would like to book Mr. Holland for an event please use the contact us section.





Furnace Destroyer #1 – Design

Heat Exchanger Destroyer #1

By: Steve Holland




Design. The first place to look if you’ve lost a heat exchanger!

Who would have ever though that a designer could ruin a heat exchanger? It happens each and every day. There are three phases of design that cause heat exchangers to fail.

  1. The manufacturer design. Many manufacturers use proprietary methods when developing heat exchangers. Carrier, for example, had a secondary heat exchanger that used a poly-propylene coating. In some furnaces, this coating failed; resulting in secondary plugging and/or heat exchanger leakage. The Lennox Pulse was another that ran into a few issues. Today, we are seeing many designs that may pose failure in the future. Understand this, most heat exchangers fail as a result other than manufacturer design.
  2. The designer of the job. At Mr. Holland’s we call these folks “Comfort Advisors”. Many comfort advisors fail to properly measure duct systems, or fail to perform load calculations, resulting in pre-mature heat exchanger failures. This is why we require all of our comfort advisors to measure the home, measure duct systems, and, in some cases, perform a static duct pressure reading on the system.
  3. The install designer. Every furnace built and designed must be installed by the installation technician. This means that after the manufacturer builds the unit, and after the comfort advisor sizes and designs the job, it has to be installed. Many mistakes are made at this phase of the process, resulting in pre-mature failures of heating and cooling systems.

Poor Static Duct Pressure

Homeowners Advice:

Never assume that just because your neighbor referred a company or the fact that an HVAC company has been in business a very long time that the job will be done properly. Pay attention to the following:

  1. Was a load calculation performed by the sales person?
  2. Did the sales person examine the ducting and perform a cfm or static duct reading?
  3. Are they accredited by the BBB?
  4. Make sure that the installing contractor gives you a complete workmanship guarantee in writing, and a host of other guarantees.

Poorly Installed Duct System

Contractors Advice:

  1. Hold your sales staff accountable by making sure that they perform a load calculation and duct calculation.
  2. Stand behind your work
  3. Spend the extra money and get BBB (Better Business Bureau) accredited
  4. Quit being so cheap. Spend money on training, education and staff development

Manufacturers Advice:

  1. Don’t be arrogant and think that your engineers are smarter than HVAC techs. They may know physics and properties of heat transfer – but, some simple changes from HVAC guys can give that furnace a better and healthier life.
  2. Use more stainless steel and good quality stainless. Many secondary heat exchangers fail because they are not made of stainless steel.
  3. Listen to your end-user customers. That’d be me and other HVAC contractors out there that install your equipment each and every day.

I hope that the information that I provided was useful. Remember, the best way to keep homeowners and customers safe is by training and educating service technicians.

Steve Holland

“Changing the HVAC industry – one tech at a time”


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Why do heat exchangers fail?

Heat exchangers fail for a number of reasons. Here’s a brief run down that will help you as a technician or a homeowner.


A furnace heat exchanger serves mainly two purposes.

1. Purpose number one is to keep exhaust fumes from entering your home via the air stream. Safety.

2. To absorb the energy from the burned fuel. Then it is moved from the metal heat exchanger to the building via a duct system. The blower moves air across the heat exchanger thus exchanging the heat from the furnace to the house. Efficiency and comfort.

Picture of a heat exchanger

Why do Heat Exchangers Fail?

1.   Lack of airflow is the number reason. Result of a poorly sized duct system, oversized furnace, dirty filters, dirty coil or a dirty secondary coil.

2.   Manufacturers poor design

3.   Poor installation

4.   Lack of regular routine maintenance

5.   Oversized or over fired furnace

6.   Age. Furnaces will wear out. That’s a fact.


Why all the buzz about failed heat exchangers?

Most companies will tell you that it’s because you can get sick or die from carbon monoxide poisoning. Though, this is possible it is less likely today as the newer furnaces are designed with more safety controls and most likely will shut down under a failure. However, heat exchangers fail in a number of ways thus the safety concern is no longer the only concern.

Here is a list of concerns regarding a failed heat exchanger.

1.  Safety. Failed heat exchangers can cause an unsafe situation.

2. Comfort. A failed heat exchanger can cause the furnace to run a different cycle time. This can cause comfort issues.

3. Efficiency. With the unstable costs of energy a plugged or malfunctioning heat exchanger can gobble up your money. It’s no different than running the water if you pay a municipal sewer and water bill. You are purchasing a fuel to heat your home. If the heat exchanger is not absorbing the heat correctly this can cause an increase in your utility bill.

4. Other failures. If your secondary heat exchanger is plugged this will cause additional wear on your blower motor causing more electrical consumption and may cause a premature failure of the motor.


What are the most common heat exchanger failures?

1.   Cracks, fractures, pitting, holes and ruptures

2.   Hot spots, warping, bulges and heat stress

3.   Plugging, corroded or sooted

4.   Manufacturers defects or poor engineering

Picture of a cracked heat exchanger

Picture of a hole in a heat exchanger

Picture of a plugged secondary

Picture of a corroded secondary

What’s the best way to protect my furnace?

1. Have it serviced – PROPERLY!

2. Change or clean your filters

3. Maintenance

Picture of a badly plugged evaporator coil

Picture of a badly plugged air filter

Picture of a dirty secondary coil

Picture of a dirty blower wheel

Written by: Steve Holland of


Steve Holland is a 25 year industry veteran and owns several Heating and Air Conditioning Companies in Wisconsin. Mr. Holland’s Heating and Air. Bloedel’s Heating and Cooling. Holland Heating and Air Conditioning. Steve is a featured speaker at many tech schools in Wisconsin and is available for training, conversation and a host of other business growth and development topics.


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