Cold air coming from our vents when the furnace and fan are off
We build a house 1 year ago and when the temperature gets below 50 degrees outside we start getting cold air coming through 4 vents of our house. All vents are on the opposite side of the house than the furnace. The colder the outside temperature gets the more air we have dropping from the vents. This happens within 15 minutes of the furnace turning off and we usually have about 2 hours between cycles so you can imagine how cold the 2 rooms get until the air kicks on again. The company says our house is doing a convection thing and they said although they have only had this happen once or twice ever that it is a normal thing that happens. The bad thing is that the vents we get the cold air dropping from are directly over my bed and directly over my 4 year sons bed. Can anybody tell me if this is normal, should you have that much cold air coming out of your ducts? The duct work and furnace are in the attic.
that is odd....is there a flue damper installed???
when in doubt swap it out....NOT!!
They installed a damper in one of the air returns, but it did nothing. They also installed a damper in one of the ducts close to the vent, but there wasn't enough force to open the damper and we weren't getting air at all so we had them remove that one also.
Have the installing company come out to look and see if they sealed up around the duct where it come trhu the attic ceiling or the wall cavity which I bet thats where the cold air is coming from. While your up there you might want to check and see if your outlets in your ceiling are in fact sealed up as well to keep the cold air from dropping down into the conditioned space. Or you can get a couple of cans of that Great Stuff foam spray in a can and seal them up yourself, that foam spray is some wonderfull stuff, I've used alot of it and sealed up many air leaks around my basement sill box areas and other penertration. For $3 or $4 per can you can't go wrong using it to sela up crack and crevice's.
Ah yes, the "I don't really understand what's going on so it must be normal" chestnut. Yet more evidence why it would not hurt certain HVAC contractors to learn a little building science. We are in the comfort business, after all, not just selling boxes.
Originally Posted by jrprint
My own house has ducts in the attic. They are round metal ducts clad with fiberglass insulation wrapped in foil. They do not drop cold air on me through the supply registers between furnace cycles. That is normal.
At least two things can contribute to your problem:
There is also the possibility your house interior is in a negative pressure in respect to the outdoors, such as would happen if a bathroom or kitchen exhaust fan is left running, or a dryer is in operation. This can draw air from leaking ducts in the attic.
- Ducts in attic are not sealed tightly. Any pressurization of a naturally ventilated attic (through ventilation openings in the structure, such as soffit vents, gable end vents, or ridge vents) via wind outdoors can drive cold air into any unsealed areas within attic ductwork.
- Air handling unit/furnace in attic is also not sealed tightly, whether it be via the plenums attached to the furnace, or access doors on the furnace unit itself.
Whatever the cause, rest assured that what you are experiencing is not normal! That is, it wil not be a normal experience if the ductwork is sealed properly.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
shophound, DanW13, actuator, thank you very much for replying. You have confirmed what I thought. Thank you for helping out a person who knows nothing about HVAC!!
Not normal at all and it certainly sounds like a deficiency in the installation, insulation and sealing of the duct system or an access panel for the furnace / air handler is not installes properly. Additionally, if an outside fresh air / make up air duct is connected to the return air portion of the system. Pressure differentials between inside and outside could be drawing in the cold air in the off cycle. There are special inline dampers available to rectify this situation but at any rate, the contractor needs to address the problem. You can bet if he was sleeping under that ceiling vent he'd fix it!
A good HVAC tech knows how, an educated HVAC tech knows why!