Where is the hot air going?

[Walter R.]

I had a new gas hot air furnace installed in my attic. The installer/contractor sealed any obvious leaks in the 25 year old duct system in my attic. My ceilings are well insulated.

Today, the outside temp is 55, in the garage (nonheated, non insulated) it is 60, in the house it is 72 and in the attic the temp is 70.

Seems to me, the attic should be just about the same temp, maybe a tad higher, than the garage.

How can I find out where my ducts are leaking? Can I do a "smoke test" myself? Any suggestions?

[tom]

Go and feel the ducts for warm air escaping. Tape the leaks. Increase insulation, and add ventilation. I think. Tom

[Tony Hwang]

Hi, I don't see anything wrong. Is your furnace supposed to heat the attic? I guess not. Attic needs good ventilation and insulation from rooms down below. Tony

[CJT]

Was it sunny today where you are?

[Walter R.]

That's a possibility. The sun was shining all day. Maybe the tile roof stored a lot of heat and is heating the attic this evening.

I will check the temps again around 2 AM

Thanks

[CJT]

Another thing to think about is whether your furnace has a pilot light. With the (relatively) small volume of the attic, the pilot can make a difference, especially if there's not much wind to help ventilate the attic.

[RP]

You can perform a homemade version of a *blower door test* that will show whether you have any significant leakage in the supply duct system. This might be the first order of business, since your method of determination of leakage above is a bit ambiguous. Solar heating can go a long way in a well insulated attic. At the conditions that you gave your attic temp may be normal. On cold days heat radiates up into the attic, from the space, and on hot days heat radiates down into the space from the attic. It follows that at some moderate ambient temp the space and attic temps will be equal.

To see if you really have a duct leakage issue: On a calm day just crack one window open a few inches, making sure all other windows, outside doors, and other openings are closed. Turn on only the indoor blower of your furnace. Observe differences in air movement through the cracked window with and without the blower running. The difference in air volume through the cracked window should be close to the air leaking from the ductwork. This will depend upon the cumulative size of any and all other structural air leaks. Because of this a wider opening in the window will produce a more accurate measurement, but at the same time will make it more difficult to check air volume changes since the velocity of the air moving through the window will be reduced as the opening is increased. If you notice a definite change in air flow through the window between blower on and blower off, then you have duct leakage worthy of concern. If the change is so low that you are unsure whether there even is a change, then you probably don't have leakage worth concern.

hvacrmedic

[m Ransley]

Are ducts sealed with mastic or tape. Are ducts insulated properly. Sun will heat the attic. How good is insulation, what zone do you live in. It may or may not be normal.