Thread: gas furncace into what appears to be wood chimey

I inspected an non-permitted gas fireplace in a garage today and the vent really concerns me. It appears that the gas furnace vents into a wood stove chimney.



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I'm not too worried about the chimney. Looks like stainless steel assembly. Oversized for the furnace size but since the furnace is power vented should work out. Might end up with some condensation issues though. The chimney install isn't ideal but seems to be the least of worries.
My bigger concerns would be lack of fire separation to combustibles around furnace, unit doesn't look like its raised above the floor level 18" and I don't see any ductwork.
Is the furnace just blowing wild, do cars pull towards the furnace, whats the gas line like, is there a return duct or just an open circular path between return/supply sides?
Write it up as a potential fire hazard, non-conforming install and liability concern.

Originally Posted by Markus Keller

I'm not too worried about the chimney. Looks like stainless steel assembly. Oversized for the furnace size but since the furnace is power vented should work out. Might end up with some condensation issues though. The chimney install isn't ideal but seems to be the least of worries.
My bigger concerns would be lack of fire separation to combustibles around furnace, unit doesn't look like its raised above the floor level 18" and I don't see any ductwork.
Is the furnace just blowing wild, do cars pull towards the furnace, whats the gas line like, is there a return duct or just an open circular path between return/supply sides?
Write it up as a potential fire hazard, non-conforming install and liability concern.

There is no duct work. This is in a detached garage as a heat source just for a garage.

As mentioned then its about safety and fire hazard. You should be writing it up as a hazardous condition

Originally Posted by Markus Keller

I'm not too worried about the chimney. Looks like stainless steel assembly. Oversized for the furnace size but since the furnace is power vented should work out. Might end up with some condensation issues though. The chimney install isn't ideal but seems to be the least of worries.
My bigger concerns would be lack of fire separation to combustibles around furnace, unit doesn't look like its raised above the floor level 18" and I don't see any ductwork.
Is the furnace just blowing wild, do cars pull towards the furnace, whats the gas line like, is there a return duct or just an open circular path between return/supply sides?
Write it up as a potential fire hazard, non-conforming install and liability concern.

Assuming that is an 80% furnace, then it is not power vented. Induced draft furnaces are negative draft appliances and rely on the chimney for draft. If it is a 90% then its just plain wrong.

I'm not so lenient on over-sized liners and vents. The resulting condensation can sometimes take real toll on the venting system and sometimes the repairs can be real expensive.

Just a wild guess, but I'm thinking the burners are over 18" from the floor. I see gas furnaces in garages all the time.

I don't see a draft hood, but it could be integral to the furnace.
The clearances on the back and sides don't look sufficient.
If those elbows are aluminum, it would be against code in these parts, but if they are galvanized, they are most likely fine.
I always use a base tee, so that there is a dirt trap, rather than have everything that falls down the vent go directly into the furnace, or onto the floor.
It is impossible to tell if the burners are 18" above the floor. That would be an issue
Like the other posters said, write it up as a hazard, and also recommend that a gasfitter come in and bring it up to code.

Dave

We have what appears to be an 80% fan-assisted gas furnace vented into a factory chimney. This class of chimney is approved for use with CAT I gas appliances the same as B-vent. The size and installation, however, must comply with the mfr.s listed instructions for the appliance, the vent mfr. and the codes. At a glance, this appears to violate the 7x rule on sizing. We don't know the overall height or rest of the installation. Regarding the furnace in the garage, it must be installed per the mfr. Without any supply plenum or back pressure, the Total External Static Pressure can be jacked and cause problems with heat transfer and flue gas condensation. The open return is a code violation and a practical hazard as it can backdraft the vent causing a major CO problem. There is no stated clearance to combustibles without a supply plenum so that fails on the spot. They might be able to make this legal if they install some modicum of supply and return ducts but I'm guessing the chimney will still be too large. Since there are no liners listed for use inside factory chimneys or B-vents, the only options if too big would be to replace the chimney with B-vent or replace the furnace with a CAT IV and power vent it out the sidewall.

FYI, most factory chimney is approved to CAT I gas, oil, and solid fuel including wood and coal. Such chimney is often referred to as "all fuel chimney". See mfrs. warranties related to fuel uses. Some carry a lifetime warranty for all but coal, which often carries only a 10 yrs warranty. Varies by mfr. so don't assume.

Originally Posted by Kevin Wood

That goes against all training in the CSA Natural Gas and Propane Installation Code.

Which part? The base tee?