Gas vent pipe questions

Jerry Parson · 07-15-2012, 05:07 PM

Hi,

I'm not an inspector or pro of any kind so I'm not sure I'm allowed to ask questions here.

I'm just a dude with little knowledge, an install manual, and the internet, trying to replace an old propane swimming pool heater.

Its going in a 6x8 wood shed by the pool. The shed houses the heater, filter, pump, pool equipment, etc. Nothing else. The shed is 20-something feet from house.

My questions deal with the venting.

Installing this:
http://www.poolcenter.com/jandy-legacy-LRZE-IO.pdf
(page 13 and 14 are venting pages)

Figure 5 on page 13 is exactly what I'm looking at, except in a smaller building (I do have all required wall clearances).

The heater came with a 2-3 ft draft hood that is single walled. The pipe going through the shed roof is double wall Type B.

The new heater can't sit in exactly the same spot as the old one so I will have to make up some offset. With help from the hardware store guy I got some Type B adjustable elbows and vent pipe and it all should line up fine.

The questions came with the bill. The double wall adjustable elbows are $70 each. Ouch! This project has gone over budget long ago. The single wall adjustable elbows are $8. I really need that $124 back.

In the heater manual (pg 14) it says that "Type B double wall or equivalent vent pipe is recommended for the entire venting system. However, single wall metal pipe may be used within the structure in the latest edition of the National Fuel Gas Code ANSI Z223.1".

So...

1) What are the reasons for double wall?

I've seen several mentioned on this site and others.

It allows a 1" clearance space going through the ceiling instead of more (2" or 6" - not sure which).
In colder weather it helps the heat rise/flow of hot gas.
Its safer in the event of touching.

Are those all the reasons for double wall?[/SIZE]

I have to replace the roof panel and re-cut a hole for pipe anyway so does the 1" clearance really matter to me since I can do whatever is needed?

I live in Washington state where it does get cold in winter. But heater won't be used then. Its only used in summer when its warm so does the climate part matter to me?

Nobody will be in shed so does the safer to touch matter to me?

In my mind those are all a NO which would allow me to use single wall. Agree?

2) If having double wall is so important why is the draft hood single wall? It doesn't seem consistant to me to go from the factory required single wall hood to a double wall. Seems like it defeats the purpose (other than the 1" clearance one). So apparently its ok to mix single/double wall, right?

If I did want the 1" clearance through the roof hole and single/double can be mixed then can I just go with the required single wall draft hood, into the cheaper single wall adjustable elbow, into a single (or double wall if I wanted) pipe, into another cheaper single wall adjustable elbow, into a double wall pipe up through ceiling to cap?

It just seems like I can get by with the single all the way through but the 1" gap sounds best. So using the double wall through the roof and the single everywhere else should be ok, right?

I'm not good at explaining so I know I repeated myself some. Sorry. Just trying to be clear.

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**John Kogel** · 07-15-2012, 06:27 PM

You are buying elbows from the wrong dealer. They don't have to cost that much.
Duravent Type B Vent Pipe Elbows

You don't need adjustable, BTW. If you can find 45 degree fixed elbows, use them and adjust the straight lengths to match.

Go with double wall full length. You want to end up with a professional installation that you can be proud of, not something you have to make excuses for. You can't switch back to single wall elbows, it won't work.

The heater may be coming on to heat water when there's no one around to keep an eye on it. Make sure it's safe.

Jerry Parson · 07-15-2012, 07:32 PM

Thanks for the info John. I would like it done right so prefer the double wall. Its just the cost. I did check your website. The 7" I need is actually $4 more there

It does look like I got the 90deg and the 45deg is almost half price so maybe I'll look into that. Unless I can find a 45deg fixed, that is. That website doesn't seem to have fixed. I'll look more.

I just went with what the hardware place had. The local Home Depot and Lowes didn't even have that.

Let me ask you one other thing. Does the pipe have to be perpendicular before going through roof or can it go out at the 45deg and then go perp?

Originally Posted by John Kogel

You are buying elbows from the wrong dealer. They don't have to cost that much.
Duravent Type B Vent Pipe Elbows

You don't need adjustable, BTW. If you can find 45 degree fixed elbows, use them and adjust the straight lengths to match.

Go with double wall full length. You want to end up with a professional installation that you can be proud of, not something you have to make excuses for. You can't switch back to single wall elbows, it won't work.

The heater may be coming on to heat water when there's no one around to keep an eye on it. Make sure it's safe.