Peculiar smell from new central AC system?
March 24, 2014 1:48 PM   Subscribe

Ever since we had our new air conditioning system installed, we get a strong chemical smell throughout the house when the furnace runs. What’s causing this? Can we do something to make it stop? If not, how long do we wait for it to go away?

The AC system in our townhouse died at the end of last summer, and we put off getting it replaced until now. We had new inside and outside units installed last Tuesday, even though the actual cooling function can’t be tested yet since the weather’s too cold here in Northern Virginia. The furnace is still fine, so it hasn't been replaced.

Problem is, now every time the furnace runs to heat the house, we get a strong, unpleasant chemical smell coming out of the vents. I’d describe it as something like charred butterscotch. It’s giving my wife and me both a headache, and it’s been going on more or less unchanged for a week now.

We’ve had techs from the installation company out twice now, and they’ve both said that they’re not sure what it is, but they don’t think it’s toxic, and it should disappear with time. (How long, they couldn’t say). The second and more senior tech said that it’s normal to have unusual smells with a new HVAC system, and suggested that it smelled like the insulation which lines the new inside unit.

My theory is that the inside unit being heated by the furnace underneath it is causing some outgassing of volatiles left over from the manufacturing process, which is not the most comforting thought.

Has the hivemind encountered this sort of problem before? How long did it take to resolve itself, or was there a problem that had to be fixed? If it’s just a matter of waiting things out, then we will, but we want to be sure this is a problem that’s actually going to go away. Thanks, all!
posted by McCoy Pauley to Home & Garden (5 answers total)
Is this a heat pump?

Does the smell only occur when the thermostat says "AUX HEAT ON" as opposed to just "HEAT ON"?

Heat pumps have an electric auxiliary heater that is used when it's too cold outside for the heat pump to do normal heat pump-y things (I'm not technically versed in the HVAC field). This often produces a smell, particularly if there's dust on the element (which usually happens over the summer when it's not being used, so the first few times you use the heat you'll smell this).

I'd imagine this could also happen with a new heat pump, for construction/manufacturing dust, and that that would be a worse smell.
posted by tckma at 2:04 PM on March 24, 2014

Thanks. Nope, it's a gas furnace. The most recent tech double-checked the furnace and blower for anything that might be overheating or burning dust. I do know the burning-dust smell you're talking about from the first time the furnace is switched on in the fall, but this doesn't smell anything like it.
posted by McCoy Pauley at 2:53 PM on March 24, 2014

If they don't know what it is, they can't know it isn't dangerous.

Can you run the blower but not the heater? Close the gas line if you need to.
If it's outgassing (which'll happen at any temperature), the smell should be strongest when you first turn on the blower. If this is the case, then open the windows (yes I know it is cold) and try to pump the nasty chemicals outside.

If it doesn't smell until the fire starts, then I would say that is pretty serious.
posted by flimflam at 3:50 PM on March 24, 2014

I think the local gas company will be happy to check the smell out for no cost, and they're not trying to sell you anything. The fire department will do the same. The top concern for both is your safety, and your safety is questionable at this point.

When I managed some apartments a few years ago, I'd have to call one or the other from time to time and they were right there in no time with their air monitors and tools, which were pretty amazing at locating the source of a problem - in minutes.

The fire dept is especially helpful if you don't know what the smell is, and the gas company is very good at checking the unit for proper connections, etc. Both are familiar with your setup and with your company.

I'd consider giving one or the other a call if I were you - probably the fire dept first, who will determine if there's any danger. If not, then I'd call the gas company to check the system and the way it's hooked up.

I woke up in the front yard with the EMTs trying to get myself and my 3-year-old daughter out of danger many years ago from monoxide, which had slowly backed up into the house from a gas heater which required a 6" vent pipe out the back - someone had put in a 4" pipe and stuffed a rag around the outside of it to hold it in place. True, there's no smell to monoxide, but other chemicals can be dangerous, too - and if you can get it checked by someone for no cost, it only makes sense to do it.
posted by aryma at 6:16 PM on March 24, 2014

Thanks for the suggestions. flimflam, that's a good thought: we've confirmed that running the blower without the furnace on still produces the smell, so it's not a function of something burning or being heated. It is also definitely not a gas leak -- we know what that's like, and there's no sign of a mercaptan smell.

I also ran across this discussion, where someone reports a similar smell from an old Carrier unit where the inside insulation is falling off and being burned up in the furnace. That seems to support the theory that the insulation is what we're smelling, although it's not being burned in our case. The installer cut a hole in the side of the new unit to reinstall our humidifier, which may have disturbed/exposed the insulation more than usual and caused the greater smell.

At this point I'm reasonably confident that we know where it's coming from and that it's not going to kill us, but I'm hoping somebody's experienced this particular problem and has an idea how long it takes to go away...
posted by McCoy Pauley at 12:11 PM on March 25, 2014

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