Thread: Exhaust vents under a deck

The systems room containing 4 water heaters (3 provide hydronic heat for radiant floor heating, and 1 for DHW), is an exterior room off a walk-out basement. After original construction, a landing was added off a wrap-around deck, that is over the top of this systems room. So, now the 4 exhaust vents are under the deck landing. The nearest door or window is at least 16 feet away.
I know lots of standards for exhaust vents on roof, near windows, etc, but is there any concern about an exhaust vent under a deck (not immediately near a door or window)?
The whole thing just doesn't seem right, but I'm having trouble thinking of a specific violation of standards. My first thought would be heat damage, but I know from experience that the temperature of exhaust from a 36,000 BTU water heater is nowhere near high enough to torch the deck. There is plenty of air movement under the deck landing. There is no visible indication of heat damage on the underside of the deck. I know clearance requirements for B-type vents, but is there a clearance requirement for an exhaust hood?
Terry

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What I've seen happen: rapid corrosion of galvanized joist hangers and accelerated deterioration of pressure treated lumber - it does not rot, but it splits and warps as a result of being "steamed".

That would also be considered a living area now and those vents cannot be under there.
People sitting on the deck above will be breathing exhaust fumes.

In floor convective heating.....

I've seen the same things as Michael as far as the deck goes. Doesn't work out well for the lumber or hangers.
- I'm guessing those are natural draft vents? draft effect significantly reduced or eliminated
- I always right it up as D&H if a water tank is involved, if only boilers I write it as potentially D&H. The problem as I see it is that people may be sitting on the deck or kids playing on it and breathe in the exhausts. Especially if it is kids. Fall or spring, kind of cool out, kids notice the heat and decide, 'lets play over here where its nice and warm'. Kids are playing on the deck floor just sucking in the exhaust. With the boilers its the same hazard in the fall or spring.
I don't mince words on these set-ups because the lawyer won't mince words when someone gets poisoned.

I agree, it is not right. It does not look like it would be that hard to route the vents out to the open, a few elbows and pipe. A solid floor cover on the deck would be good as well.

Those stairs need a handrail. Or is it two handrails?

Perhaps they did it that way so that the snow would not accumulate and they would have a heated deck for winter use!

Originally Posted by Terry Beck

The systems room containing 4 water heaters (3 provide hydronic heat for radiant floor heating, and 1 for DHW), is an exterior room off a walk-out basement. After original construction, a landing was added off a wrap-around deck, that is over the top of this systems room. So, now the 4 exhaust vents are under the deck landing. The nearest door or window is at least 16 feet away.
I know lots of standards for exhaust vents on roof, near windows, etc, but is there any concern about an exhaust vent under a deck (not immediately near a door or window)?
The whole thing just doesn't seem right, but I'm having trouble thinking of a specific violation of standards. My first thought would be heat damage, but I know from experience that the temperature of exhaust from a 36,000 BTU water heater is nowhere near high enough to torch the deck. There is plenty of air movement under the deck landing. There is no visible indication of heat damage on the underside of the deck. I know clearance requirements for B-type vents, but is there a clearance requirement for an exhaust hood?
Terry

Do you always take your pants off and hang them over deck chairs while inspecting


Anyway...High concentration of flue gasses above.....and possible poor flue drafting.....Possibly a run away appliance and super heating the underside of the deck....Maybe just plain foolish. One of those have to work.

Oh yeah. Keep your pants on while inspecting. You may get more referrals.

Terry, unless you are a licensed origin and cause fire investigator, would refrain from comments such as yours about the fire hazard. So, how much heat does it take to ignite a deck? Over what time period? What qualifications do you have to ascertain if pyrolysis has taken place? Did you use a combustion analyzer to test for ambient CO while standing on the deck? Was the wind blowing?

Better stick to facts. The violate the code and product listing-period.

With direct vents there is a 12 inch clearance requirement.
Would that also apply here?

Also I imagine snow would not be an issue under the deck so thats out.

Originally Posted by Ted Menelly

Do you always take your pants off and hang them over deck chairs while inspecting

He took them off so he wouldn't get them dirty under the deck.

Originally Posted by Bob Harper

Terry, unless you are a licensed origin and cause fire investigator, would refrain from comments such as yours about the fire hazard. So, how much heat does it take to ignite a deck? Over what time period? What qualifications do you have to ascertain if pyrolysis has taken place? Did you use a combustion analyzer to test for ambient CO while standing on the deck? Was the wind blowing?

Better stick to facts. The violate the code and product listing-period.

I don't think Terry ever posted anything about it being a "fire hazard", but even if he had it is only his opine based on what he viewed.

I must admit that if I found 4 flue vents under a wooden deck I think the first thing I would think of would be a fire hazard.

Regardless of how or what is described, flue vents under the wood deck ain't right! If I had to report on this find, I think I would go the CO gas route and that it is just not a good or safe idea to have the flue pipes under a deck that is designed for folks to sit and relax on! They might be relaxing for a longtime if they are out on the deck when those critters are emitting flue gas!

Let's start off anew.

Those vent caps look like Type B Gas Vent Caps and they look like a Simpson High Wind Vent Top.

Okay, nothing was said about them being direct vent, just "I know clearance requirements for B-type vents, but is there a clearance requirement for an exhaust hood?" (from the original post in this thread).

We all know that Type B Gas Vents (which is what those are) are required to be 2 feet higher than any adjacent wall or obstruction within 8 feet. That would mean those Type B Gas Vents would need to terminate a minimum of 2 feet above the deck, however, with the deck being similar to a flat roof in that is it a horizontal plane, the minimum height above "the deck" would be 1 foot - unless there was a wall or other obstruction within 8 feet of the termination, in which case the vent would need to terminate 2 feet higher than that wall or other obstruction.

Thus it does not matter that the wood may get hot and eventually catch on fire, it does, however, matter that the vents are not installed to meet code in that they are not 2 feet above an obstruction within 8 feet.

The Simpson installation instructions state (bold and underlining are mine): "Vent pipe with 3"-12" diameter must terminate at least 2 feet higher than an adjacent wall or obstruction, if it s within 8 feet."

Scott, I was referring to this quote:

"My first thought would be heat damage, but I know from experience that the temperature of exhaust from a 36,000 BTU water heater is nowhere near high enough to torch the deck. There is plenty of air movement under the deck landing. There is no visible indication of heat damage on the underside of the deck."

Now, the case in point involved four rather large B-vents in close proximity under a poorly ventilated deck. So, commenting on the degree of heat damage would be beyond the scope of a HI and reside with a PE or Licensed fire investigator. That's all.

Honestly, I reserved commenting on the application of B-vents under a deck because it should be patently obvious it is an improper application, both from the codes & listings and as a practical matter.

Originally Posted by Bob Harper

Honestly, I reserved commenting on the application of B-vents under a deck because it should be patently obvious it is an improper application, both from the codes & listings and as a practical matter.

Same reason I waited until my post above to post ...

Originally Posted by Terry Beck

The systems room containing 4 water heaters (3 provide hydronic heat for radiant floor heating, and 1 for DHW), . . . . . . Terry

Are the water heaters for the radiant floor heat system ASME rated as pressure vessels for heating purposes?