How should 80% furnace flue vent?

[whitemow]

We are going to replace our 30 years old furnace. Our old furnace flue go out to chimeny through singal wall vent. Water heater vent also ties to it.

I got several estimates. One said that we cannot use 80% furnace, since our exisitng vent goes to chimney. The suggestion is to use 90% furnace and PVC vent can go out to the side of house.

The other 3 said that we can use the chimney, and just change the vent from singal wall to double wall. However, one did mention it is possible the chimney might be damaged many years later. We should keep the water heater vent connected to the furnace vent. It will help reduce the damage.

Any advise is appreciated.

[beenthere]

Depending on the chimney size, and weather its classified as an outdoor chimney, it may need to be lined, weather you get an 80, or 90% furnace.

[whitemow]

Currently is outdoor Chimney. The house is more than 30 years old. In the coming year, we will add-on an extension, which the outdoor chimney (wall) will be come indoor except the few feets at the top.

[beenthere]

Put a liner in it.

The water heater will need the chimney lined if you orphan it on a outside chimney, because it will condensate.

The 80% will will cause the chimney to condensate in the winter also.

[t527ed]

if it is a masonary chimney put a liner in it. if it is a single wall pipe up the outside of the house run a b vent.

[nastinad]

rip all the old venting attached to the chimney out and seal the chimney. Properly install venting. If you install 90%er then add a nice 90% water heater to tie into it. Best to stay away from chimney if possible for best results.

[contactor]

line the chimmney. make sure new vent is sized correct for an 80% furnace and w/h or orphaned w/h.

[whitemow]

I climbed up to check the chimney. It is with clay flue liner. The size is 6" x 10". I cannot tell about the vent connected to the furnace. If I have it replace with b-vent/double wall vent, with this size clay flue liner, will it do the job?

Thanks.

[beenthere]

Originally posted by whitemow
I climbed up to check the chimney. It is with clay flue liner. The size is 6" x 10". I cannot tell about the vent connected to the furnace. If I have it replace with b-vent/double wall vent, with this size clay flue liner, will it do the job?

Thanks.

Might need to use an aluminum liner.

6 x 10, is too big for a 3" water heater flue, with, or without a furnace attached.

[whitemow]

The plan is to have the water heater flue goes out with the furnace vent.

Our existing water heater vent is 3" and connnected to the furnace vent (~5"). The other side connects to the wall/chimney is about ~7".

With the new furnace, I assume the 5" and 7" vents will be replaced. Should this be replaced by aluminium vent? Should the we put in aluminium vent inside the chimeny as well?

Thanks for the advise.

[liftmys10]

whats is 80% and 90% ??

[beenthere]

Yes, drop an aluminum liner down the chimney.

Not aluminum pipe to the chimney.

[beenthere]

Originally posted by liftmys10
whats is 80% and 90% ??

80%AFUE furnace can be vented into a chimney
90%AFUE furnace can not be vented into a chimney

[whitemow]

Beenthere, thank you.

Off the 5 contractors/companies came out to give us estimates, none of them mentioned the liner. Does it tell that they properly will not provide quality installation? Or is it because we are in Georgia, it may not be the big issue?

[beenthere]

Cold be your winters are warm, so they don't worry about it.

Or they have never read the fuel gas code book.