Hello,

We recently had a new furnace installed. It's a goodman GMH8 (goodmanmfg.com).

I've read all the available documents, but can't seem to figure this one out... (I am NOT an hvac guy what so ever)

There's a 6" pipe that goes from the inside of the furnace, presumably the blower... to my brick chimney. the pipe traverses about 4 feet of distance.

4 feet away from the furnace, where it enters the chimney, the metal pipe is too hot to touch for more than 2 seconds.

where the pipe goes into the furnace, the outer metal of said pipe is too hot to touch without getting a blister.

there's some kind of vent installed on the pipe itself, which i guess is a backflow limiter of some kind... it's a balanced piece of metal that hangs vertically. it is set up in such a way that if the furnace wanted to suck air in thru that pipe (from the chimney) the hanging metal flap would not allow the air to be sucked in from the basement. alternatively, if the chimney was totally blocked up, the flap would allow air to be pushed out of this pipe into the basement.

i was able to move the flap in such a way where i could stick my hand into the pipe leading from the furnace to the chimney, i wanted to feel the air. sure enough, the air is forcibly blowing and very hot. the air felt heavy, like it would probably coat my hand in water if i left it in there long enough.

so i guess there's 2 questions: is the hanging flap installed properly?

and, why is there such extremely hot air being pushed out into my chimney and eventually out of the house?

the air coming out of my registers around the house could be hotter.... its just "warm"... it feels kind of odd to me, I think a furnace should push hotter air.

According to this there is only a 4 inch vent requirement.

http://www.acfactoryoutlet.com/Images/Productos/pdf/goodman/gasfurnaces/specs/SS-GMH8.pdf

Sounds like you have a swing damper installed on the flue connection.

With the 80% unit the chimny should have probably had a liner installed.

According to this there is only a 4 inch vent requirement.

http://www.acfactoryoutlet.com/Images/Productos/pdf/goodman/gasfurnaces/specs/SS-GMH8.pdf

Sounds like you have a swing damper installed on the flue connection.

With the 80% unit the chimny should have probably had a liner installed.

Hi there, thanks for the quick reply.

I have read that pdf and understood it as best I can, but I don't see any references as to which direction the swing should be... into the pipe or out of the pipe...

Also, how about the temperature of the air in that pipe, should it really be that hot?

but i dont see any references as to which direction the swing should be... into the pipe or out of the pipe...


Actually it is not supposed to be there

With the 80% unit the chimny should have probably had a liner installed.

Call the company that installed the unit to take care of the problems. You paid them.

That furnace has to be set up properly and from what you have posted it is not. Got 4 in to 6 in pipe and that is wrong to start with.

With a properly sized flue liner the barometric damper would probably not be needed. You may want to have the gas input and temperature rise checked, and possibly increase the blower speed. Any heat produced by the unit that is not heating your home is going up the flue.

but i dont see any references as to which direction the swing should be... into the pipe or out of the pipe...


Actually it is not supposed to be there

With the 80% unit the chimny should have probably had a liner installed.

Call the company that installed the unit to take care of the problems. You paid them.

That furnace has to be set up properly and from what you have posted it is not. Got 4 in to 6 in pipe and that is wrong to start with.

Hmm... I see... I'm guessing they installed the damper to skimp on the liner... this is one of several things that bug me about the install. Damper issue mostly figured out, please tell me about the heat going to the chimney...

I understand the hood over the water heater to route vapors/heat/moisture out the chimney, but the temperature and force of the air going from the furnace to the chimney really bugs me... it's forced air, like if a candle was in there it would easily extinguish it... if a wad of paper was in there, it would easily blow it into the chimney...

Not that I'm sticking things in my exhaust pipe, but I'm just trying to give you as much detail as I can... is it supposed to be THAT hot, sufficient enough to cause blistering when touching the outside of the pipe?

SINGLE WALL FLUE PIPE WILL GET VERY HOT ON A 80% furnace, you didn`t say if you had single or double wall pipe

SINGLE WALL FLUE PIPE WILL GET VERY HOT ON A 80% furnace,,you didn`t say if you had single or double wall pipe

Ah, didn't know a double wall one exists... this is a single wall flue pipe.

Wouldn't it be more efficient to just route this exhaust pipe back into the ducts that supply warm air to the house? Seems like a waste to have it all just leave like that.

ah, didnt know a double wall one exists... this is a single wall flue pipe.

wouldnt it be more efficient to just route this exhaust pipe back into the ducts that supply warm air to the house? seems like a waste to have it all just leave like that. Sure... it's your funeral...

ah, didnt know a double wall one exists... this is a single wall flue pipe.

wouldnt it be more efficient to just route this exhaust pipe back into the ducts that supply warm air to the house? seems like a waste to have it all just leave like that.



You and entire familey would wake up dead,, bodies all swollen up looking like they would explode

ah, didnt know a double wall one exists... this is a single wall flue pipe.

wouldnt it be more efficient to just route this exhaust pipe back into the ducts that supply warm air to the house? seems like a waste to have it all just leave like that.



Where the waste came in was,
,1st buying the 80% furnace instead of a 93% furnace, would have cost maybe a couple hundred extra at the most
2nd, sounds like a unlucky draw on installer, should have checked around and got an installer with good referances.

The extra bucks the 93% furnace would have cost would have probably been revamped in savings on the gas bill the very first year