Smoke enters home

[HVAC Jimm]

We have a gas fired dual pack on the roof. It is about 12 years old. It brings in smoke filled air from wood burning in the neighborhood. Two HVAC companies and PG&E have checked it and found no problems in operation or safety. We do not use our fireplace and the flue is closed. Smoke enters whenever the system comes on. Any ideas?

[Gib's Son]

I would guess it comes from an outside air intake. If you don't have one, then the blower door probably leaks quite a bit.

[thermojohn]

:ditto: Sounds like a smoke test free of charge.

[HVAC Jimm]

I would guess it comes from an outside air intake. If you don't have one, then the blower door probably leaks quite a bit.

Thank you Gib's Son. The companies who were out checked both and didn't find any problems.

[HVAC Jimm]

:ditto: Sounds like a smoke test free of charge.

I'm not sure what this means thermojohn but I've already had two companies and the utility check the "system". I asked one company to check the venting in the attic on a hunch that a bad seal was drawing smoke into the vent. He says he didn't find anything.

[Gib's Son]

Do you have an outside air intake? If so, that IS the problem. Any time the fan is on it introduces outside air, thus any smoke, it's doing what it supposed to do. If no intake, have some seals installed on the blower panel. These would be first things I would check and are the most likely.

Do you have exposed ducts on the roof? If so, maybe the return is not sealed or maybe even the supply could be creating a vortex and drawing in some outside air. If you are sitting on roof curb with down-shot discharge, the curb could be leaking.

I suppose another thing that could be going on is your house is under negative pressure when the system runs, and is drawing in smoke from building cracks and window weep holes. Try turning your system on and put a small piece of tissue paper or a feather near an exit door, and crack the door ever so slightly, and see which way it wants to go....not very scientific, but should give you idea.

[Gib's Son]

I'm not sure what this means thermojohn but I've already had two companies and the utility check the "system". I asked one company to check the venting in the attic on a hunch that a bad seal was drawing smoke into the vent. He says he didn't find anything.

Smoke tests are used to detect building leakage.

[chillerout1]

just how close are your neighbors?

[thermojohn]

I'm not sure what this means thermojohn

Just some trade humor. Didn't mean to confuse....

If you are smelling smoke when there is smoke outside, and your unit is running, it gives indication there is some sort of exchange happening. If it is intentional with a fresh air inlet, then that's the place. If not, you may have leaking duct work, or have other leaks in the envelope of your home that need to be addressed. My evaluation would not stop at just the unit.

Keep in mind, no home is airtight, and eventually succumbs to whatever is 'outside' of the home.

If it is indeed critical, I'd recommend a blower door test to evaluate the tightness of your home. It would make your home more energy efficient to find and reair substantial leaks in the envelope.

[genduct]

of how much air is leakiing IN from the bad fit sheet metal access panels!