inefficient heating/unsealed mystery duct

Problems related to residential installations.

inefficient heating/unsealed mystery duct

Postby Donnie2003 » Sun Jan 27, 2013 10:21 am

Hi!

Silly - I just noticed today that there is an unblocked heat duct coming out of the back of the furnace and I was wondering if this was some sort of safety function of the furnace or just an oversight of the previous owners. Was it just to provide heating for the unfinished basement where the heating is? Could this be why the force from the registers is so weak? Would it be okay to seal it up?

Thanks in advance. -)
Donnie2003
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- inefficient * mystery duct

Postby Donnie2003 » Sun Jan 27, 2013 10:33 am

My previous post seems to have had a glitch ... random asterisks have popped up deleting a number of words and I'm not sure why.

I will repost -

I just noticed today that there is an unblocked heat duct coming out of the back of the furnace and I was wondering if this was some sort of safety function of the furnace or just an oversight of the previous owners. Was it just to provide heating for the unfinished basement but was never hooked up and could this be why the force from the registers is so weak ? Would it be okay to seal it ?

- Still doing it ... for some reason it affects question marks and the words connected to them. Sigh ... not only do I have furnace troubles but even my posts about them have troubles !
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- inefficient * mystery duct

Postby Freon » Sun Jan 27, 2013 11:46 am

Sadly, due to spammers, you can not use a question mark or a dash. And URLs must be carefully done without a slash so type slash.

Your duct question is a good one. It may be there for heat to the basement so pipes don't freeze. It may be there to allow the correct air flow through the heat exchanger. You'll need to count all the supply registers and, assuming they're fed by a 6" duct, multiply the number of supply registers by 110 to see what the air flow is possible. Then tell us the size of the furnace and we can approximate if the air flow is ok. If there is adequate air flow and you don't have a need for heat in the basement, then you can close that duct in the basement.
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- inefficient * mystery duct

Postby Donnie2003 » Sun Jan 27, 2013 6:46 pm

Thanks again for the quick reply, Freon

In answer to your question there are 17 registers throughout the house. 7 on the topmost floor, 6 mid, and 4 lower (as it is a split-level home there is a lower basement as well where the furnace is located).

The make of the furnace is IDG. Input on the unit is listed as 90 MBTUH, output 68 MBTUH

I also says 115 V 60 cycles and 12 amps

Just as a quick test, I used aluminum duct tape to seal up that open heat duct, which comes out at the back of the unit pointing down between the unit and the unfinished framework of the wall behind. All it seems to do is make that area very hot. The furnace gives off enough heat in operation without needing it I think so I don't think the pipes are in danger of freezing. Even sealed up the basement feels like the warmest room in the house and it's definitely above freezing. With that duct sealed I think the registers all through the house are marginally hotter and stronger though still weakest on two registers on the upper floor furthest from the furnace. Those never worked well since we've been here.

Anyway, thanks again and let me know about the power output.
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- inefficient * mystery duct

Postby Freon » Mon Jan 28, 2013 3:21 pm

Go ahead and leave that duct closed as long as you think the furnace heat alone is enough. Now here's what you'll need to do to be sure all is good. Set the thermostat to about 5 degrees above the house temperature. You want the furnace to have a long run. Now after it has been running for a few minutes you need to go down to the basement and observe the furnace burners. What you are looking for is to see if during the next 10 to 15 minutes the burners cycle off and then back on again while the main blower continues to run. The reason you want to do this observation is to make sure the furnace heat exchanger is not overheating and thereby causing the high temperature safety switch to shut off the burners until the heat exchanger cools when the burners will relight.

What you want to see is the furnace burners remain constantly on while the heating cycle is going. If you get an on and off burner cycle then open up that duct you have taped and do this test again.
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Postby Donnie2003 » Wed Jan 30, 2013 11:16 am

I'll be sure to do what you say, Freon. Thanks again for all your help! -)
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