Draft Inducers Are All the Same, Right?

By Bill Spohn


Your goal in “repair mode” is to restore the equipment to full and safe operating conditions.  What harm could there be in using any “equivalent” induced draft blower?

Unfortunately, great harm is possible:

  • Harm to your bottom line (call backs and insurance claims);
  • Harm to your reputation (customer frustration with lock outs and early equipment failure);
  • BODILY harm to the occupants or family (carbon-monoxide poisoning).

We all understand the need to save a few bucks on parts. Whether it is savings that you keep to boost your profit margin or savings you pass along to your customer to make a quote more attractive. Managing your parts costs is a critical part of business survival.

While airflow is one of the most critical operating parameters in the HVAC world, it remains a tricky parameter to control and measure. The products must withstand the rigors of furnace operation producing a reliable airflow that EXACTLY matches what the Original Equipment Manufacturer (OEM) of the appliance (Furnace, Water Heater, Boiler, etc.) intended. In many cases, copycat designs that are reversed engineered have shown in lab testing to be inferior, as these alternative manufacturers are not privy to all the details and lab testing that went on in OEM product development. Look for replacement draft blowers built for the OEM. This will insure it meets their specifications and has been tested to match their performance requirements.

The job of the combustion air blower (draft inducer assembly) is to effectively move the hot flue gases and combustion by-products through the heat exchanger(s) and out of the house or building. Beyond the obvious need to withstand flue gas temperatures up to 450 F, the unit must mount correctly on OEM equipment, and the blower housing and impeller must be made of materials that can withstand the corrosive chemical compounds present in flue gas.

Other non-obvious factors include:

  • OEM exhaust coupling design has a strong influence on air flow rates and pressures which could have upstream impact on burner efficiency and deadly carbon monoxide creation
  •  Improper airflow rates can also impact the function of the pressure switches and other safety devices
  • An inducer with it’s own agency listing is not part of the furnace’s agency listing. A copycat inducer is not approved by the OEM for use on the furnace system and makes the furnace non-compliant with the OEM’s original agency approval.

Non-OEM approved induced draft blowers developed by reverse engineering can provide a pressure signal capable of closing a switch which then allows gas to flow. Ok, so that means it works, right?

However, the pressure signal is ONLY an indicator of the airflow. The OEM’s design actually requires a specific airflow (CFM). The OEM has modeled the inducer system to give a pressure signal as an indicator of airflow for their design only. A pressure signal in a reverse engineered inducer system does not guarantee proper airflow that is sufficient for safe operation.

In 80+ furnaces low airflow can cause condensation in places the furnace manufacturer did not intend. Corrosive compounds in the flue gas then “rain out” acidic condensates, which may then attack furnace materials, and in some cases eat through heat exchangers. The furnace manufacturer intends that the walls of the heat exchangers MUST remain intact for safe and proper operation. A compromised heat exchanger can both create and propagate deadly carbon monoxide gas.

A copycat combustion air blower that delivers too much air flow can cause combustion air temperatures in the system that are higher than the furnace manufacturer intended resulting in over-heated furnace components and shortened component life.  In particular, on a two-stage furnace, insufficient inducer airflow on low-fire can cause the pressure switch to open, which tells the furnace control to run on high-fire resulting in poor efficiency.  A copycat inducer draft blower with marginal performance on high-fire can cause nuisance trips and even a lockout until reset.

Imagine this scenario: you diagnose and replace the induced draft blower at a business or high-end home with an outdoor package unit using a copycat. One of the worst cold snaps ever happens over a time when the business is closed or the residents are away. Later you get a call regarding a million dollar insurance claim being made due to extensive water damage from burst pipes.

What’s the connection to your work you wonder? Little did you know the OEM requires a special grease for inducer starts in extremely cold weather. The wrong grease in the copycat caused the blower to run slowly and fail to make the pressure switch resulting in the furnace lockout and frozen pipes which later burst.

So, next time you go to replace a residential or light commercial induced draft blower, think twice if a cheaper unit is worth the harm it can do.

About the Author

Bill Spohn, President & CEO, TruTech Tools, LTD, is majority owner of www.TruTechTools.com and runs a consulting business, William P. Spohn, LLC, which engages in HVACR Expert Witness work, technical education and e-commerce consulting. Bill may be reached by email at Bill@TruTechTools.com.


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