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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


The Plugged Secondary Heat Exchanger – Destroyer #6

Furnace destroyer #6 – The Plugged or failed Secondary!

In our Rapidtech Heat Exchanger Program, we teach technicians all about heat exchangers and their safety. In this destroyer post we will cover the plugged secondary heat exchanger .

Furnaces and boilers must transfer the heat from the burned fuel to your home or to the space that is to be heated. This is done by heating up an object and then passing water or air through or across that object allowing the heat to transfer. Thus, the term HEAT EXCHANGER.

All forced air condensing gas furnaces use two heat exchangers. The main heat exchanger is the primary heat exchanger and the condensing heat exchanger is called the secondary.

When we talk about heat exchangers failing, often times technicians and homeowners only think of the cracked heat exchanger. This is not always the case.

Here is a list of different types of heat exchanger failures:

  1. The cracked heat exchanger
  2. The pitted, rotted, rusted out heat exchanger
  3. The heat exchanger with holes in it
  4. The sooted primary heat exchanger
  5. The plugged or rotted secondary heat exchanger

If a technician shares that he or she has found a failed secondary heat exchanger the proof is easy to find. Here is what will happen or what you may notice if you have a plugged secondary heat exchanger

  1. The carbon monoxide readings in the exhaust will be elevated and sometimes off the charts
  2. The furnace will not run properly
  3. There may be water leaking from the lower portion of the furnace
  4. You may smell sulfur or a rotten eggs smell at the exhaust or near the furnace
  5. The drain hoses and furnace drain trap may be black or a dark brown

Is this dangerous? The chances of getting carbon monoxide poisoning is slim. However, if your furnace has a plugged secondary, I guarantee it will not make it through a heating season. I highly suggest that you get it repaired or replaced as soon as possible.

What causes the plugged secondary?

In 26 years, I have seen a number of plugged secondary heat exchangers. Most that I have found were because the polypropylene coating started pulling away from the metal causing a restriction and eventually a full blown clog. I have seen propane furnaces where the furnace was not burning properly thus causing soot and eventually caused a clogged secondary. Then there was a time when I found things like bees getting into the pipes and making the secondary a home.

Causes of failed secondary heat exchangers

  1. Breakdown of polypropylene
  2. Over-fired furnace
  3. Undersized duct system
  4. Improper air fuel mixture
  5. Lack of maintenance
  6. Normal wear
  7. Life cycle of that furnace has finally come to an end

Homeowners advice.

If your furnace has a secondary heat exchanger that is pitted, rotted or plugged it’s time for repair or replacement of the furnace.

Technicians advice.

Check secondary heat exchangers on EVERY call. Perform a combustion analysis on every gas furnace repair and maintenance call. If the secondary heat exchanger is the finned style make sure you check it for cleanliness and be sure that it is not restricting air. If you are seeing carbon monoxide readings in the exhaust above 200 ppm, this is reason to investigate further.

If you would like to learn more contact us regarding our Rapidtech Heat Exchanger Certification Program.



Furnace Destroyer #4 – The AC Coil

Heat Exchanger Destroyer #4 – The Air Conditioner Evaporator Coil

In the operation of HVAC equipment there are relationships between components that are too often overlooked. What does the furnace heat exchanger have to do with an evaporator coil (A-Coil) from the air conditioning system?

Air flow – is the common link!

Over a period of several years, the evaporator coil of an air conditioning system will collect dust, dirt and debris. It’s inevitable that the coil will need service at some point. Imagine 400 cubic feet of air per minute passing through the coil above your furnace. Multiply that by 3 or 4 tons of cooling and that number quickly becomes 1200 to 1600 cubic feet of air per minute. It’s not a matter of if the coil will get dirty – it’s a matter of when will it need a good cleaning?

Not all technicians inspect the evaporator call on every service call. The best practice is to inspect all heat exchangers and at the same time inspect the evaporator coil for dirt and debris. The evaporator is located directly in the same air steam as the heat exchanger. If the evaporator coil becomes dirty the airflow across the heat exchanger will be reduced resulting in additional and unnecessary stress to the furnace. This is another relationship that will destroy a furnace’s heat exchanger.

In our business – we call this; The Heat Exchanger Destroyer #4

Here are some technician tips and musts when having a furnace or air conditioner serviced:

  1. Inspect the entire heat exchanger
  2. Inspect the evaporator coil
  3. Check the filter

Tips for homeowners:

  1. Hire qualified, educated and knowledgeable technicians
  2. Ask questions
  3. Ask the technician to show you the evaporator coil or heat exchanger
  4. Have your system service annually and in some climates twice per year
  5. Avoid the advertising that offers a too good to be true deal – like the cheap $39, $49, $59 or up to $99 tune ups. These usually are too good to be true resulting in important steps being skipped.
  6. Get to know the company that you are working with. Visit their websites and call their owners. Build a relationship of trust.


I know that this picture is a little extreme. However, it really came from a home in Milwaukee, Wisconsin. Realize that even a little dirt or debris on the surface of an evaporator coil can decrease airflow and result in higher utility bills and lower performance.


The worse A coil that I've ever seen. PLUGGED

The worse A coil that I’ve ever seen. PLUGGED

Taken directly from the Mr. Holland’s Heating and Air Conditioning best practices library.


Some questions and comments from homeowners:

“Can I clean my own evaporator coil?”   –  Yes. However, it’s unlikely that you will have the necessary tools to perform an airflow adjustment and refrigerant charge analysis. After any coil is cleaned your air conditioning system will require airflow adjustments. Plus, you will need to know how to access the coil without damaging refrigerant lines and cracking the plastic drain pan.

“My air conditioning guy said that I only have to check this if my unit is not working (my coil is in my attic).”  FALSE. Get a new air conditioning guy! Typical HVAC companies rarely check the evaporator coil on maintenance visits. This is a MUST on every tune up!



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, Air Conditioning and Duct Cleaning Scam

Scam Video Fox 6********  SCAM ALERT  *******

Though not directly related to furnace safety or heat exchanger safety – BEWARE.

There is a company calling homeowners in Wisconsin, offering a $35 air conditioning tune up and duct cleaning special. This is a scam!

The caller may have a foreign accent and the call will be an out of state call.

If you receive a call like this – HANG up. Do not give any information over the phone


Steve Holland

Mr. Holland’s Heating and Air Conditioning