inside-corner issue for direct vent

[RustyShackleford]

Hi folks, new member here ... professional engineer, but not plumber. I'm adding a room and must relocate my direct-vent water heater (I mean the type that vents horizontally out the side wall of the house, with a co-axial pipe that brings in combustion air from outside, but is *not* powered by any sort of fan).

Unfortunately, if I bring the side vent kit straight out from the water heater, it violates the "clearance to inside corner" spec for most of the units I am looking at. (My existing one is 25 years old, so I expect I'll just buy a new one; I'll be buying a similar 40-50gal 40K btu/hr unit). Some units want the clearance to be 12" and others 18"; others just say "follow the building code" and the building code says "do what the manufacturer says" - kind of a Catch22. I'll stick to units with a 12" spec, and I'll have about 12" to the center-line of the pipe, but the spec seems to want it to be to the edge of the termination flange.

I'm wondering if I can angle the horizontal part of the vent kit, so the termination will be farther from the inside corner. Of course, it'll penetrate the wall at an angle, and look kinda funny. Is it possible to add a 45-degree elbow, after the 90-degree elbow that transitions the water-heater exhaust to horizontal, so the pipe goes straight thru the wall, but offset from the center-line of the water heater ?

Any other ideas ? I suppose I could just come out the roof, but I like the side vent - avoid another roof penetration, and my house is pretty tight so I like the idea of bringing in external combustion air.

Thanks much !

 

[IFIXH20]

If you are over 12'' ,than I think you will be ok. (12'' is the minimum if i'm not mistaken).
why do you need to angle the pipe? Just extended to the correct height and 90 towards the outside wall.

 

[RustyShackleford]

If I go straight out the outside wall, I dont have 12". I do from the center-line of the pipe, but not from the edge of the hood thingy at the end, which is how the clearance is usually shown in drawings.

It's because the water heater is in the corner of the new room, right up against the wall of the existing house. I allowed 25" width for the cubby where it'll go, so I can have a 22" diameter unit with enough clearance around the sides for a drain pan to fit (I guess a drain pan for a 22" unit would be no more than 25" diameter ?) So if I go straight out, the centerline of the pipe would be 12-1/2" from the wall of the existing house. I attached a drawing.

I *really* don't want to push it out farther into the new room, it'd just take up space for no reason. I'd rather go out the roof. But I'd really like to make the side vent work.

Thanks.

View attachment water heater.pdf

 

[IFIXH20]

Rusty, That is a combustion system with the potential for carbon monoxide poisoning. I would follow manufacturer spec./installation to a tee. Improper flue can be very danagerous.

 

[RustyShackleford]

I would follow manufacturer spec./installation to a tee. Improper flue can be very danagerous.

Yeah, I know - thanks. I *am* trying to follow the spec. I'm wondering if it's ok to achieve this by either angling the pipe outwards (away from the inside corner) or using an additional low-angle (e.g. 45 degree) elbow to offset it.

 

[LiQuId]

on most days i would be better on this, Today the sun has beatem me into mush somewhat.

I am sure you would have no issues using a single 45' it would reduce the allowablle run by a percentage, if I were less sun haggard I would look this up in the book for you I will attempt this tomorrow and hope this thread bump prompts somebody else to do the page work.

keeping in mind also that I am in canada, and the gas code could be different in your area.

 

[RustyShackleford]

Thanks much. I imagine the laws of physics are similar in Canada, at least I think the code here pretty much defers to the specifications of the manufacturer - and all of those I've looked at just sidestep the issue of angling the pipe through the wall, and omit entirely the idea of adding a 45-degree (or less) elbow to get the offset (which probably means it's not allowed).

So I think the way to go is a flexible vent kit (for direct-vent) I've seen from some manufacturers. I read the installation manual for one:

http://www.bradfordwhite.com/images/shared/pdfs/manuals/238-48146-00A.pdf

... and they completely sidestep the whole issue of actually bending the thing and in particular if a *compound* bend would be allowed. You can imagine making two 45-degree bends that would accomplish what I'm trying to do - offsetting the place where the pipe penetrates the house wall so that it's a few inches farther away from the inside corner - and actually have equal or less flow restriction than the single 90-degree elbow of the usual rigid side-vent kit. I can't really see a reason for having a flexible kit if not to allow this sort of thing.

 

[IFIXH20]

Pull this site up , look at page 17 - figure 27. www.hotwater.com/.../promax-direct-vent-manual (186589-004). The inside corner is 18'' min. with this heater.

 

[RustyShackleford]

Thanks for the link IFIXH2O, but it seems to be broken (and I can't figure out how to get to where you got manually). Perusing various direct-vent units, I do recall seeing ones with an 18" spec (for inside corner clearance) but 12" seems more common.

Depending upon what it's possible/legal/recommended to do with the flexible coaxial vent kit, 18" should be doable too.

 

[RustyShackleford]

Bingo, I think I've found something that works.

Check out:

http://www.statewaterheaters.com/lit/im/res-Gas/186589-001.pdf

... in particular, Figure 26 on page 18.

It seems to show that I can run the pipe parallel to the wall (after the 90-degree bend just above the water heater that makes the pipe horizontal) far enough to get the inside clearance, and then another 90-degree bend to make the angle perpendicular to the wall before it exits.

In reality, if I use a flexible vent, I can do it with two much smaller bends and be way better than shown in the figure.

 

[RustyShackleford]

But I'd like other choices. Bradford White has one with a flexible vent, but the instructions don't say anything allowing (or forbidding) an offset:

http://www.bradfordwhite.com/images/shared/pdfs/manuals/238-48146-00A.pdf

 

[LiQuId]

after reviewing the Natural gas code book, i can find no reason that you couldnt use a 45 on the horizontal. Most of the codes say what youre finding "check with manufacturer" which would be a good idea, try phoning them to acertain their opinion. sidewall venting is better acomplished with a vent motor as winds and pressure differentials can cause flue gas spillage without. keep in mind that flexiblle vent is corrogated and offers more flow restrictions and turbulance than smooth metal inner wall. IMO you would be best using a 45 on the horizontal to accomplish your run, If I had a vent that exited through the roof existing I would surely want to use it over a sidewall.

just to clarify, ( after re reading the first post ) you are talking about vent piping that Is the vent exhaust AND the combustion air inlet on the same pipe ?

also, dollars to doughnuts A high efficiant hWt will save more than a side vent will.

 

[IFIXH20]

Bingo, I think I've found something that works.

Check out:

http://www.statewaterheaters.com/lit/im/res-Gas/186589-001.pdf

... in particular, Figure 26 on page 18.

It seems to show that I can run the pipe parallel to the wall (after the 90-degree bend just above the water heater that makes the pipe horizontal) far enough to get the inside clearance, and then another 90-degree bend to make the angle perpendicular to the wall before it exits.

In reality, if I use a flexible vent, I can do it with two much smaller bends and be way better than shown in the figure.

You need to go with figure 27 on page 18. ---See NOTES (B) on page 18.
Instead of 45's being north & south -- Run Them east & west and that should give you close to 20''. I would double check with the manufacturer,as i have not ran to your situation. AO Smith has the same spec. as State.

 

[RustyShackleford]

You need to go with figure 27 on page 18. ---See NOTES (B) on page 18.
Instead of 45's being north & south -- Run Them east & west and that should give you close to 20''. I would double check with the manufacturer,as i have not ran to your situation. AO Smith has the same spec. as State.

Figure 27 doesn't apply to my situation - I don't need to get past any joists - nor do I want to combine "condition 1" and "condition 2", as prohibited by note B.

By "east & west" maybe you mean to do what is shown in Figure 27 but turn it on it's side ? That makes sense. Although I could get by with one 45 by just rotating the 90 on top of the tank by 45 degrees, and then straightening it out with another 45 just before entering the wall.

Looks like AO Smith is just the parent company of State. Hmm ...

 

[RustyShackleford]

... sidewall venting is better acomplished with a vent motor

Don't want motor, if possible, noise in home office.

keep in mind that flexiblle vent is corrogated and offers more flow restrictions and turbulance than smooth metal inner wall.

Yeah, but my run is WAY below the 80" maximum suggested for offset arrangements, and close to the minimum of 30" where they want a restrictor added.

If I had a vent that exited through the roof existing I would surely want to use it over a sidewall.

just to clarify... you are talking about vent piping that Is the vent exhaust AND the combustion air inlet on the same pipe ?

Yes, I am talking about the co-axial pipe arrangement. In fact, the main reason I want to stick with the side vent is because I like getting the combustion air from outside, as my house is very tight.

But you're making me wonder if there are venting arrangements that allow roof venting but still have the co-axial thing (direct-vent). If so, I'm being a dope for agonizing over this side-vent inside-corner issue, because a roof exit is quite feasible - well, depending on the spec for clearance from a much higher nearby wall. (Actually, after checking, I think the roof vent is *more* problematic than the side vent. That same wall that creates the inside-corner issue on the side vent is within 10ft and I'd have to go way high to clear it by 2ft - the typical spec).

also, dollars to doughnuts A high efficiant hWt will save more than a side vent will.

So they're more options for direct-vent units designed for roof venting ?

Thanks everyone, for taking the time to help/educate me.

 

[IFIXH20]

Figure 27 doesn't apply to my situation - I don't need to get past any joists - nor do I want to combine "condition 1" and "condition 2", as prohibited by note B.

By "east & west" maybe you mean to do what is shown in Figure 27 but turn it on it's side ? That makes sense. Although I could get by with one 45 by just rotating the 90 on top of the tank by 45 degrees, and then straightening it out with another 45 just before entering the wall.

Looks like AO Smith is just the parent company of State. Hmm ...

I do not think you can add another bend with that true 90 in figure 26 -- That's why I say Figure 27 should work for you. Good luck.

 

[LiQuId]

http://www.hotwater.com/water-heaters/residential/conventional/gas/vertex/power-direct-vent/

not saying this one specifically, but condensing heat exchangers are more efficiant as they use the condensation's latent heat. for efficiancy check the AFUE rating and go from there, in this example 96% efficiant think of it like this, regardless of how its vented .96c for every dollar you spend goes into the house and you lose only .04 cents
combustion air Always comes from outside in one way or another.
As for saying your house is "tight", regardless you are bringing combustion and ventillation air in from outside memory fails me right now but I believe the minimum acceptable COMPLETE air exchanges per hour are 2 so to further the efficiancy curve even more a boiler and a combi core HWT is still best bet as you can heat your house with radiant and not lose the heat in the air when it exchanges. ( this is why carwashes use radiant tube heaters ) many years back they built some of the first R-2000 houses near my area and it wasnt long before they realized that they had to bring ventilation air in or else the condensation would detroy everything inside the houses. it was kinda funny cause there were million dollar houses that looked like greenhouses with dew on the windows from outside.

but your best bet for efficiancy in all cases would be a boiler for your heating AND hot water needs though this option is pricy it pays off quick.

Don't want motor, if possible, noise in home office.

insulate the wall better and dampen the sound, I just installed a hot water tank with an inducer fan in a similar situation as yours and You cant hear anything when the mech room door is closed.