Hello, I have a typical gas furnace, 80% efficient, so it uses achimney. A 4" metal flue pipe comes out of the front/top of thefurnace, wraps around towards the back towards the wall behind which isthe chimney. Total of about 6 feet of 4" flue pipe, looks properlyinstalled. The 4" pipe goes into an 8" pipe which goes into the wall,and the chimney is inside the wall right there.My gas bills are horrendous I should add.Tonight for some reason I felt the flue pipe while the furnace wasrunning and the thing is hot as blazes. Even at the end of the 6' runof 4" pipe, you can't even keep your finger on the flue pipe for morethan a couple seconds cause it's so hot.Is there some way to capture this heat ? If so, what do I look into ?I must be heating half the country.Thank you !

Rip it out and install a 96% furnace. The problem with using something like a heat recovery ventilator to capture your lost heat is that further cooling of the flue product will result in vapor condensation and will simultaneously interfere with proper draft. By the time you call in an engineer to resolve these issues and make the modifications safely, you could've replaced it with a more efficient unit. Not only that, but any modification will raise liability issues that wouldn't be in your favor.Richard Perry

Heat loss from furnace via flue ?

Feb 06, 2006 23 Replies

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RP 20 years ago

Here, I googled it for you.

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"[...] The DOE's technical definition of AFUE is as follows:

The measure of seasonal or annual efficiency of a furnace or boiler. It takes into account the cyclic on/off operation and associated energy losses of the heating unit as it responds to changes in the load, which in turn is affected by changes in weather and occupant controls. "

Richard Perry

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hallerb 20 years ago

I will have to ask my friend who taught HVAC. He said more efficent is better, and likes 90+% variable speed furnaces, but did note going from my present 69 to 93 will NOT cut the gas bill by the percentage it appears. Have several friends who replaced their furnaces and noted exactly the same thing.

Bill went down but not as much as anticipated:(

heat pumps cost way more to operate than forced air gas

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RP 20 years ago

Your gas bill isn't proportional to your gas usage. There are other charges besides the gas charge. Additionally, if you have other gas appliances, then you have to prorate your fuel usage accordingly. You can't just take the total bill and multiply by 24% to get the estimated energy savings for the new unit. Sorry, but it isn't that simple. :)

Not around here they don't.

Richard Perry

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julie japczyk 6 years ago

replying to roger61611, julie japczyk wrote: My flue goes out the side of basement wall

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