Heat loss from furnace via flue ?

[roger61611]

Hello, I have a typical gas furnace, 80% efficient, so it uses a chimney. A 4" metal flue pipe comes out of the front/top of the furnace, wraps around towards the back towards the wall behind which is the chimney. Total of about 6 feet of 4" flue pipe, looks properly installed. 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 was running and the thing is hot as blazes. Even at the end of the 6' run of 4" pipe, you can't even keep your finger on the flue pipe for more than 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 !

[RP]

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

[Mark & Mary Ann Weiss]

You can try a flue damper, to prevent cold air from backing down into your gas furnace.

Grainger may have just what you're looking for:

-- Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION Hear my Kurzweil Creations at:

sites at:

[buffalobill]

general info for your furnaces:

[whodat]

"My gas bills are horrendous I should add"

join the club

keyspan/lipa what ever the hell its called now, raised gas 40%, .thats with a mild winter.

is this warm air heat you have?

you normally cannot hold on to a flue pipe from any heating appliance, unless its one of thos 94% high efficiency warm air jobs.

theres nothing to retrofit a gas flue pipe with.. unless its a boiler that will accept an electric stack damper, that doesnt save on running time, only off time as it prevents the chimney from pulling on the hot boiler.

[hallerb]

They USED to sell something like what she or he wanted, but cooling the flu gas caused mega troubles and some deaths.

about the best you can do is a automatic flue damper, it closes when the furnace isnt running,

just think every furnace exhauts a heated air out the chimney 24/7

just think of that when you pay your gas bill

[scott21230]

Some of those electrical heat sinks on the flue might warm up your basement a little bit. Other than that, a more efficient furnace might be the best bet. More insulation would help too.

[roger61611]

I was afraid I might be stuck between a rock and a hard place. We have one really good HVAC company in town, I'll see what they think. Also may take some infrared pictures to see if there's more leaks I don't know about. My furnace is only 8 years old and is 80%, so canning the whole thing and going 96% is a money hit I was not prepared for.

I wonder if having half my vents shut (to redirect most of the heat to one end of the house) could affect things.

If this warm winter was typical I'd be tempted toward heat pump, our electrical rates are low here but at 40 deg N latitude, heat pump is a tough one.

[m Ransley]

An aftermarket damper must have a lockout to the furnace incase it doesnt open, There have been alot of cases where they failed leading to Co issues. I think the cost will be excessive compared to a new unit with a starting high efficiency, meaning payback is poor. You could be reducing furnace efficiency and harm the furnace if closing vents increases temp rise to much. A friend bough a house where the ac coil was clogged shut, he removed it to clean it and his bills dropped in half. You really need your system serviced to find out if it is running optimaly and go through your options for an upgrade.

[roger61611]

I had it serviced, it runs fine, that is, it's working exactly as designed.

I would dearly love to bag our gas company and go heat pump and electric hot water - is that a ludicrous idea in Columbus Ohio ? Maybe I'm too emotional about my $400 gas bills.

Thank you !

[mm]

I hHadn't thought about that before you just mentinoed it.

What does one do when his AC coil is stuck inside the duct and not accessible? Is that common? Did the guy you mention have to cut a big hole in the duct to clean his coil?

I had to cut a little hole in my duct just to see why the condensate was dribbling all over the floor, instead of going down the pipe.

My coil has never been cleaned, and I suppose there is a good chance it is dirty, clogging the system and wasting fuel.

Remove NOPSAM to email me. Please let me know if you have posted also.

[barry]

Depending, exhaust temp might not be _that_ high. For one thing, depends on sensitivity of your digits.

For many, 150F is considered limit for "sustained" contact. For a flue pipe, that's pretty cold. To recover much more heat from the exhaust, you'd better be prepared to deal with condensate, corrosion probs, etc.

Were I you, I'd suggest obsessing on all the many ways your house and its occupants waste energy. Get a good clock thermostat, and see just how much setback you can handle. Electric blankets work great, a/r, I'm told.

J

[Brian]

There used to be 82% and even 84% efficient furnaces, but manufactures learned very quickly that cooling flu gasses cases big problems....

Don't listen to who ever suggested replace it with 90%.....

Waste of money. So if you currently pay $350/month you would save 35$ - 40$. That is stupid. Go with dual fuel HeatPump.

I am getting rapped by Vectren too. Switching off is the only answer.

[Bubba]

If you bought the furnace 8 years ago then you decided to go cheap and now you are paying for it. If it was in the house when you moved in then you have basically nothing into it. Stop gripping. Gas is high. Electric is too. Insulate, weatherstrip and turn the heat down as cold as you can stand it. Otherwise, replace it with one of the 90+% efficient furnaces and or add a heat pump to it. Either way, its all money. You just have to decide who you want to give it to. Bubba

[scott21230]

Get a geothermal heat pump. More efficient than a regular heat pump, and no need for electric backup.

[udarrell]

The system installer(s) should retrofit evaporator coil access door plates when coils are in ducts. Encased coils should be manufactured with easily removed access panels; we should demand this be done! Clean coils are an absolute must condition!

The manufacturers' ought to consider the required future service and maintenance necessary to efficient and long life operation of their brand of equipment. All A/C equipment should also be manufactured for easy static pressure testing before and after the evaporator coil and the return air filter.

servicing advantages could be their strongest marketing selling points!

- udarrell - Darrell

[m Ransley]

BrownTiger , your miss under standings and inaccurate statements are all to common among the masses, an 94.5% unit is 18% more efficient than an

80% unit. That is 18% savings at todays Ng prices. You really can`t be that ignorant to think Ng won`t double again in 10-15 years, it always has and always will. Therefore his Payback will be great even considering lost interest . What do your investments and interest on money return you.

[trader4]

Oh, so I guess they stopped making anything more efficient than 80%?

Since when is saving $40 a month stupid? Now if you mean he may not come out ahead by replacing his current furnace, that depends on how much it will cost and how long he will be living there.

Well, I guess you don't mean the economics I mentioned above, since now you say it's OK to just replace what he has with a heat pump. And the fact that he already has high gas bills should be a clue that a heat pump would likely be even more costly to run in that kind of environment.

[hallerb]

ahh 90% or whatever efficeny rate is under 100% operation, time wise!

In most cases a furnace doesnt run continiously, so 90% isnt reached.

high efficency furnaces start the blower when the gas turns on, blowing what feels like cold air, when the customer complains the on temp is increased for cmfort, but it lowers efficency.

all of these have to be considered in the mix

[RP]

DOA. Google AFUE to find out why you're talking nonsense.

Richard Perry