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Brandon Whitmore

Any separation wall or venting issues here?

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How about:

G2425.7.2 Connection to factory-built fireplace flue. An

appliance shall not be connected to a flue serving a factory-

built fireplace unless the appliance is specifically

listed for such installation. . .

(or is that not a "factory-built fireplace"?)

If that flex vent connector is single-wall, it doesn't belong in an unheated garage. 2427.10.2.2

The sizing of the common vent is probably tricky with three appliances. I'd look at the sizing tables carefully.

Otherwise, I'm stumped. I see nothing else in chapter 24 or chapter 3 that would prohibit this.

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There's a possible separation issue where the duct-work penetrates the ceiling. I'm not in front of a code book, but I'm thinking it's not allowed for the induced draft furnace to share a flue with natural draft appliances.

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I'm thinking it's not allowed for the induced draft furnace to share a flue with natural draft appliances.

I'd like to know the answer to that. If it is a prohibition, by extrapolation of what I've seen, there are likely several hundred thousand installations in this area that violate such a prohibition.

When I see it, I'm careful to check for back-drafting at the natural-draft water heater - at the draft hood. It usually back-drafts for several seconds until the flue heats-up, and then all is good. The techs around here accept this, as do I. (Sometimes, the back-drafting does not, at all, stop, and of course this is flagged.)

By the by, what's a natural draft "AWH" water heater?

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I commonly see furnace and water heaters with shared flue. I typically see "wye" connectors vs a straight T. I would question the gas fireplace, In my ten years I have never seen one that's doe's not have it's own flue.

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There's a possible separation issue where the duct-work penetrates the ceiling. I'm not in front of a code book, but I'm thinking it's not allowed for the induced draft furnace to share a flue with natural draft appliances.

Yes, they are allowed to be combined but certain rules do apply.

Download Attachment: icon_adobe.gif JB Column 1.pdf

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Download Attachment: icon_adobe.gif JB Column2.pdf

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There's a possible separation issue where the duct-work penetrates the ceiling. I'm not in front of a code book, but I'm thinking it's not allowed for the induced draft furnace to share a flue with natural draft appliances.

Yes, they are allowed to be combined but certain rules do apply.

Download Attachment: icon_adobe.gif JB Column 1.pdf

68.84?KB

Download Attachment: icon_adobe.gif JB Column2.pdf

74.46?KB

Good articles. When I get to my books, I'll look into the appropriate rules and follow up here with some section numbers.

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I swear there was a vent connector wall penetration prohibition in the past. There still is, if one were to follow various manufacturer's installation instructions.

The closest I could get in chapter 3 of the ORSC (IRC planning section) was the one prohibiting "duct" openings in between the house and garage. While the vent isn't truly a duct, it's still an opening that communicates between the house and garage.

Natural draft and induced draft units can share a vent connector. The code basically now just says the positive pressure portion of the airflow from the induced draft can't affect natural draft equipment.

Here's why I don't like this one:

I was there to an emergency response call. The customer was having intermittent odors in the house near the fireplace. The fireplace has not been in use since 2011 (valved/ capped). Under certain conditions, if the house could pull air in from the garage (CO, etc.). Also, let's say the common vent were to get plugged while the furnace was running poorly. Byproducts of incomplete combustion would blow back down into the house.

I know it's wrong, but don't know if I can say the code says so. At least not any more.

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I swear there was a vent connector wall penetration prohibition in the past. There still is, if one were to follow various manufacturer's installation instructions. . . .

You might be remembering 1803.3.1 which, strictly speaking, doesn't apply to gas appliances.

M1803.3.1 Floor, ceiling and wall penetrations. A chimney connector or vent connector shall not pass through any floor or ceiling. A chimney connector or vent connector shall not pass through a wall or partition unless the connector is listed and labeled for wall pass-through, or is routed through a device listed and labeled for wall pass-through and is installed in accordance with the conditions of its listing and label. . .

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I received a response to this question from the state of OR Building Codes Division. Please understand that this answer is relative to this exact problem, and that input should be gathered from the local AHJ.

"While this isn’t a duct, it is a penetration between the garage and the occupied space that should meet R305.2.

Also, the pertinent sections of Chapter 24 of the ORSC that aren’t being met are:

  • G2407.2 and G2407.4 for combustion air. Obvious that there isn’t adequate combustion air; the occupied space is at a negative pressure to the garage, especially with the fireplace not operating (the pilot light might reduce some backdraft by drawing heat/vent air flow up the fireplace vent)

  • G2427.3: Positive flow required for any vent. The “home” is obviously at a different pressure than the garage, and the system is back-flowing into the home. The maximum “negative pressure” (draw) of the water heater and furnace will be about -0.05”.  The interior of the home can have bath fans, kitchen fans, temperature difference between the warm home and the outdoors (creating stack effect pressure similar to that created by the vented flue), wind effect, etc. that can easily overpower the draft up the water heater to the roof vent outlet, especially when just the pilot light of the water heater is the only heat source in the vent system.

The system is not meeting code. Are you still in contact with the customer? They should be made aware of the possible hazards; we hope they have working carbon monoxide detectors. I’m unaware of a method to equalize the pressure between the garage and the living space, since a duct/opening can’t be made between the living space and garage (per ORSC R305.2)."

  • Like 1

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It is permissible to share a single flue among more than one heating appliance or fireplace. But it’s very important to apply safety constraints while doing this.
 

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On 7/5/2018 at 7:27 AM, dennispalmer said:

It is permissible to share a single flue among more than one heating appliance or fireplace. But it’s very important to apply safety constraints while doing this.
 

Thanks, Dennis. I think that rule covers appliances in the same room. And I think the water heater flue in this picture meets the rule. But the issue is with the fireplace flue coming in from another room. Also there is the clearance of the pipe to the wall material and the need to seal that wall, 3 violations so far.  😒

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