It is fan assisted. There is no hood. Here is an example
Interesting and wow! That throws off all my BPI training.
This: “Category I Venting is venting at a non-positive pressure.” and this “A furnace vented as Category I is considered a fan-assisted appliance and the vent system does not have to be gas tight,” seem to be exact opposite. One has negative and the other positive flue gas pressure.
Then this, “Single stage gas furnaces with induced draft blowers … allowing, in some instances, common venting with natural draft appliances (i.e. water heaters)”. This one throws me totally based on my training. I’d definitely refer it out, despite manufacturer recommendations; or at least I’d include a direct quote of the manufacturer recommendations in my report.
Okay, a positive system, such as a 90% furnace cannot draft naturally. The gases are too cool. They have to be pushed and have positive pressure. Positive pressure would force exhaust out of any cracks or holes in the exhaust (which is typically PVC material).
Fan assist is barely a breath of push, it is only minimally assisting in the rise and will not force gases through small holes…it operates much more like a gravity draft and less like a positive pressure exhaust (which sounds like a jet engine in comparison).
I am ready to be corrected by the pro’s but that is my laymen understanding.
So in the end, can this be vented through the wall or does it need to vent above the roof line?
I’d like to do an ambient air CO level reading in that furnace room. With the furnace running, I’d also like to run some smoke around the flue connections. I’d definitely recommend a CO alarm placed in that furnace room, major or safety concern.
I’m on alert now to seeing this arrangement in the future.
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In my state, only above the roof line. This would be flagged in my report for the sidewall vent.
We had two separate conversations at once. Sidewall clearance from openings for 90BTU appliance and sidewall venting.
Also, I think the mfg instructions are a bit confusing. It covers the horizontal run ratio which was confused with the horizontal sidewall termination. There is no sidewall termination option in the mfg instructions.
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My report too but solely based on the B vent. Is that your criteria, or something more?
With an atmosphere vented appliance, there are standards for minimum draft pressure. It can be tested, but it always is negative. With this flue gas fan assisted furnace approved for connection into a single chimney with an atmosphere vented water heater, I’d definitely like to see what the draft pressure of the water heater was when the furnace was running. Apparently, the manufacturer has tested this condition. I definitely see a red flag if that arrangement is present.
I have 3 sources. The manufacturer, the IRC and the UMC.
The manufacturer says
induced draft blowers draw products of combustion through a heat exchanger allowing, in some instances, common venting with natural draft appliances (i.e. water heaters)
Common venting with draft assist (not positive pressure) is very common in my area. I see it nearly every day.
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That’s the key right there. Whether it has fan assist or not doesn’t really matter. A cat 1 furnace with or without fan assist is not considered a positive pressure vent.
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Thanks.
Where’s a good image of the model number?
Post # 7 shows the model #.
You don’t even have to Google the owner’s manual to figure out the efficiency. 72,000 output divided by 90,000 input = 80%%. That and the single B-vent flue eliminate it being a high efficiency furnace.
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Please excuse me, Jeff. I might be missing the point.
Are you referring that the stats I posted are only for high efficiency furnaces?
Looking forward to understanding.Regards.
Yes, that is what I am saying.
Morning, Ryan. Hope to find you well.
It is early in the morning and I wanted to double check everything. I think I have it laid out properly.
I went through the data sheet. INSTRUCTIONS for
[GMS8, GDS8 and GHS8 GAS FIRED WARM AIR FURNACE SINGLE STAGE] INSTRUCTIONS FOR *M(H,S)8 / GD(H,S)8 / GHS8 / GME8 ADS(H,S)8 / AMEH8 GAS FURNACE)
PAGE 9: Venting - Furnace Installed in Horizontal Position
THIS FURNACE IS NOT DESIGN CERTIFIED TO BE HORIZONTALLY
VENTED THROUGH AN EXTERIOR SIDE WALL.
The furnace is a vertical / up flow position.
THIS FURNACE MUST BE CATEGORY I VENTED.
Category I - Vent pipe requirements
For Category I appliances, NFPA 54, Chapter 12 allows for
the use of single wall, double wall, B-vent flue pipe or even
a chimney.
So what’s causing zinc oxide to build up on the furnace cabinet exterior? Seems like Brian was onto something.