I didn’t think that one could vent a gas hot water heater into the same line with an HVAC system? Isn’t that a NO NO?
Brian this is a very typical configuration. I am wondering why you have never seen this in your 21 years of experience in construction? Your website says you have “multiple certified experts”.
Unless you’re seeing something different than I am all I see is one water heater appliance flue connector and one appliance single wall flue pipe connecting to a B vent fitting. One may call the the “V” in the HVAC system.
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Yep, very common installation in my area.
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While you are getting up to speed, you have clearance issues as well.
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The two plumbers I spoke with said the opposite. I further explained to them that when I started up the exhaust fan on the furnace you can feel the backdraft out of the water heater flue. I don’t know if it is because the house is sealed so well and backdraft is common or the wind was blowing creating the issue or that is normal. You could light a match and the backdraft would blow it out. There have been previous posts about these issues with no concrete answers. So I guess some backdraft is acceptable when one appliance is on and the other isn’t?
What did they say exactly and what was their method of correction?
You finally mentioned some more information such as the furnace may be a fan assisted furnace. Did your plumbers tell you that a fan assisted furnace cannot tie into a natural draft water heater flue pipe?
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Looks like it to me. The fan just assists the natural draft process. This is a byproduct of increasing efficiency by a few percent.
My understanding, this cat. 1 appliance is not considered a fan assisted unit. Do you concur?
A category one appliance would be non condensing and no pressure. The fan is to assist draft and not pressurize.
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Got it. I often see cat. 1 common vented with natural draft water heaters. I seldom see cat. 3 anything. (except commercial), so the OP’s exhaust statement threw me.
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The key takeaway is a fan assisted furnace will assist the furnace with combustion. There will be a slight boost for the flue draft as well. A cat 1 appliance will utilize flue connectors and B vent piping material with unsealed connections. It’s a non condensing and non pressure system.
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It was poorly presented and the follow up post revealed a little more information.
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Induced draft furnaces sharing a flue with a natural draft water heater is a common topic for HVAC contactors and plumbers to argue and dislike. A few years back I followed a lengthy discussion on an HVAC message board and what I remember was that the amount of time exhaust gas spillage out of the water heater vent opening (at the China hat) occurred was brief so it was allowed. This is often why you’ll see the melted plastic rings around the pipes on top of the tank (I still write that up anyway since I’m not sure that’s the cause).
Many on the thread I referenced speculated that sharing a vent with a mechanical and natural draft appliance would soon be disallowed but it doesn’t seem to have happened. It’s becoming less common (in my area anyway) since nearly all of the furnaces are going to high efficiency PVC venting. Many of the water heaters are tank-less and have their own vents as well.
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Great sketch… funny it specifies single-wall vents prior to were they joint and it’s from 2012. Single-wall pipe was phased out in my area 25+ years ago. Not that it isn’t allowed, I think the installers just go tired of getting the clearance compared to double-wall. Do you guys see newer installs with single-wall?
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The OP post had single wall for what I assume is the furnace. This image is close to his situation. Often the home we inspect are 20-40 years old so this image is relevant for the time.
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