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I moved into a house about 2.5 years ago, and the previous owners had a heat pump installed, together with a gas furnace. Recently I had my furnace repaired (faulty igniter) and the HVAC technician said the installation was done against code because the heat pump was connected to the return air pipe, instead of on top of the furnace. He said I could be "red tagged" with a B-type warning and be required to fix this within 45 days.

Is that true? Why would they have installed it into the return air pipe if that's against code? are there health risks with this? I use the heat pump (hot mode) when it's between 0 to 15 degrees C outside, just the furnace when it is below 0, and the cold mode heat pump when it's above 35 C.

What are my alternatives for fixing this? Can a contractor just fix the pipe to go to the right place?

I am located in Toronto, Canada.

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  • If you want to know whether it might be against code, you'll have to specify where it is, since codes vary by locality. You could go inspect the paperwork from when it was done, for some insight. Hard to tell from here if the HVAC tech was just trying to "scare" up some business using "Fear Uncertainty and Doubt" or on the level. I'd lean towards the FUD explanation until some evidence is provided otherwise.
    – Ecnerwal
    Mar 1, 2014 at 21:58

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The tech made it sound worse than it is. It's not in the wrong air flow, just the wrong order, so moving the pipe will not help. It's a fair sized duct, not a pipe.

There is a restriction in at least the International Mechanical Code about heat exchanger coils being before the furnace. It is because in cooling mode, the resulting condensate can be corrosive. In heating mode the physics involved are not really a problem, but that doesn't change the code.

There is an exception to this requirement, it is OK to configure the system this way if the appliances are listed for such configuration. You would need to obtain the installation instructions and see if this is indicated as an option.

The only practical way to fix this if you cannot prove the current configuration is allowable is to relocate the heat pump coils upstream of the furnace.

Note that the direction of airflow is the criteria for placement, not above or below.

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  • Thanks! Do you know if relocating the heat pump coils to be upstream of the furnace is an expensive job? Are we talking bellow $500? I am in the Toronto,Ontario (Canada) area if that helps.
    – Steve
    Feb 28, 2014 at 19:42
  • Off the top of my head I should think 500 would cover it, but I'm not current with HVAC labor costs. The time it takes also varies widely depending on existing conditions. The only way to find out is get some quotes from local outfits.
    – bcworkz
    Mar 1, 2014 at 21:20
  • Thanks bcworkz. The furnace is from Fridigaire, and heat-pump is from Gibson, and both brands seem have an affiliation with Nordyne? I am wondering if that's the reason the installation was done like that, but couldn't yet find documentation to support it. My fear of getting HVAC people to do quotes right now is if they red tag me and shut off the furnace (it's average of -15 C right now). I might wait when it gets warmer.
    – Steve
    Mar 3, 2014 at 15:23
  • There's no real danger in heating mode, the risk is only in cooling mode. So take your time and do thorough research before bringing anyone in. I've no idea what "red tag" might be or if it's really a thing, I've no experience in Canada. I suspect if it's anything, it would come from either a building or utility inspector, not independent contractors. When the time comes for quotes, I doubt it will be an issue, but what do I know?
    – bcworkz
    Mar 4, 2014 at 12:46

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