Attic Gas Fired Forced Air blows cold starting

[Richard A. Moran, 2nd]

This is my house but it has bugged me since moving in 4 yrs ago. My home has two heating/AC systems, one in the basement and the other in the attic. Both are forced air gas fired systems. The unit that serves the second floor blows cold air for about 4-5 seconds in the Winter each time it runs. I understand that the ducting is located in the unheated attic and it makes complete sense that I would get a short blast of cold air whenever it first comes on but it just seems like a design problem. This is my first home with a heating plant located in the attic. Is this a common complaint?

Dick

[rramsey]

Very common. I have heard it hundreds of times in 40 years of HVAC work.
Every one is so spoiled to central air. Imagine what our grandparents went through & we complain of a little cold air.

[cbottger]

Not a lot of options here don't know how old your furnaces are; your fan can be powered up either by time from a solid state board which is not adjustable but if you have an older furnace that has a heat activated fan switch which is adjustable the setting can and often is down around 90 degrees and that is to low I preferred mine to be above 100 and can set as high as 115 this allows the heat to rise up the plenum into the duct before the blower motor starts. Other than that your only option is to add more insulation to your duct work within the attic.

If your furnace is a horz in the attic your probally SOL

[Richard A. Moran, 2nd]

The "fix" I use to get around this problem is to install those plastic air diverters on the two ceiling vents located over our bed. Instead of washing down the windows and on to our bed it deflects the air into the room. Maybe not the best solution but it is cheap and almost invisible.
Thanks for your replies,
Dick Moran
MD HI #29927

[David A. Andersen]

Insulate the duct more.

If the duct is on the attic floor, cover it with insulation.

The attic is a crappy place for the hvac no matter how you look at it, but saves you a closet!

Just perceive this, heat transfer rate is directly relative to the temperature difference inside and outside the duct. Q= 1/R * A * Delta T

For every degree difference there is one multiplier involved. 5 degrees is 5x faster.

Insulation only slows things down, but it may keep the air in the duct warmer between cycles. Also if the air registers are in the ceiling, warm air will rise up into the duct and if insulated more, will not be lost to the attic and when the furnace starts the air will be warmer.

Rolls of foil faced duct wrap are wider and easy to use and will also reject heat in the summer. The batt insulation is much more effective than loose fill.

The expense may be more than you are bothered by the draft!