How not to vent a Gas condensing boiler

Jim Robinson_2

SuperTech

Lol. It just needs a little more RTV

nibs

Thought I locked the door before I left.

Jean-David Beyer

Do not gas condensing boilers require two "vents," one for air supply and one for exhaust, so that the differential pressure between them is extremely low?

nibs

My Rinnai E50 allows for using room air.

Steamhead

Once again- you can't fix stupid!

Ironman

Are you kidding? What idiot did this?

JUGHNE

Any pictures of the rest of the install?
Homeowner job?

EBEBRATT-Ed

Probably not a homeowner. Most of them have more sense.
RTV coated flue. Must be a new design.

I am surprised the off gassing from the curing RTV didn't take someone out.

Grallert

I think that Viessmann allows for room air, I guess that's why the cover is off.

Leonard

that RTV burns,

not knowing any better I used it to line a rusted exhaust suction fan cavity on a Carrier nat gas flat roof HVAC unit we owned. When I tested it red hot burning bits of red "fire-proof" RTV blew out........ I replaced it.

Alan (California Radiant) Forbes

Jean-David Beyer said:

Do not gas condensing boilers require two "vents," one for air supply and one for exhaust, so that the differential pressure between them is extremely low?

Grallert said:

I think that Viessmann allows for room air, I guess that's why the cover is off.

They could also have removed one or two of the rubber flaps on top of the boiler to allow air in.

mikeg2015

Jean-David Beyer said:

Do not gas condensing boilers require two "vents," one for air supply and one for exhaust, so that the differential pressure between them is extremely low?

We use room air on most install of furnaces and boilers unless it’s a very tight home. Too many service calls for plugged intakes to make it worth the minimal impact or the cost of extra piping. Code requires it on some cases.

But code book writers and inspectors don’t have to clear frozen intakes when it’s -15F outside in 2’ of snow.

NY_Rob

If you're venting with PVC and are in an area where snow buildup/blockage is a concern, you could always install a Cleanout Tee with Cap in the intake piping and just remove the cap for as long as needed if it becomes necessary. No going outside to shovel.

FWIW- I have read regarding mod-cons that it desirable to use outdoor air for combustion vs. indoor air whenever possible because the outdoor air is generally "cleaner".

https://www.supplyhouse.com/Spears-P444X-030-3-PVC-DWV-Cleanout-Tee-w-Standard-Plug

mikeg2015

Outdoor air is cleaner so long as there’s no grass clippings. But lint and dust would be less and chemicals depending on location. Downside is bugs getting in. We’ve just found we have dramatically fewer issues using indoor air all around and of course you can offer a slightly lower installed price.

The clean out is a good idea on longer runs.

Slimpickins

When it says it allows room air you first have to do the math and determine if you have enough cubic feet to allow it. You're really doing your customer a dis-service by not bring intake air into the appliance unless it's absolutely impossible.

Leonard

Seems a plus to using interior air in cellar is ventilation ..... if have radon, mustiness, etc......

ChrisJ

Not that I'm defending this disaster but most red RTVs are rated to be used at 600 degrees F and the only "off gassing" would be acedic acid which smells like vinegar from the RTV curing. Once cured I wouldn't expect any smell.


I wouldn't think you would be venting at 600+ into that vent.

Like I said, not defending anything in that picture.

mikeg2015

Slimpickins said:

When it says it allows room air you first have to do the math and determine if you have enough cubic feet to allow it. You're really doing your customer a dis-service by not bring intake air into the appliance unless it's absolutely impossible.

It’s not a disservice if there are fewer call backs that way. These are not tight construction cookie cutter modern homes.

That combustion air gets heated regardless of where its introduced, direct or indirectly. So there no change to net system efficiency.

We use 2 pipe where it’s nessesary. Most of these installs were previously B vent or chimney vent furnaces at one time, and most were just gravity coal furnaces before that.

plumbbob

whats wrong with it it looks great

Timco

Can I play?

Timco

I'll add this beauty....

Jean-David Beyer

And the inspector passed this?

ChrisJ

> @Jean-David Beyer said:
> And the inspector passed this?

That's a 50 50.

Are you surprised if one did?

Leon82

> @Timco said:
> I'll add this beauty....

Is the intake teed into the exhaust?

ChrisJ

> @Leon82 said:
> > @Timco said:
> > I'll add this beauty....
>
> Is the intake teed into the exhaust?

EGR.
It helps cool peak combustion temperatures which allows a leaner mixture without knocking.

Leon82

It's like they saw a diagram of the concentric vent and moved it to there.

That couldn't have run more than a few seconds before it started convulsing

mikeg2015

Leon82 said:

It's like they saw a diagram of the concentric vent and moved it to there.



That couldn't have run more than a few seconds before it started convulsing

You think they opened the manual?


Easy fix since it’s not newer tight construction. Just make it 1 pipe.... assuming HTP/Westinghouse allows that.

Jean-David Beyer

Are you surprised if one did?

Not really. One inspector approved my new heating system when there was a 12 foot (or so) long piece of bright yellow CSST gas pipe going straight across the garage (where my heating system is) that was neither bonded nor grounded. A different inspector approved the condensate drain just dumping the condensate on the ground outside. Another inspector ... . The list never ends.

Timco

Leon82 said:

It's like they saw a diagram of the concentric vent and moved it to there.



That couldn't have run more than a few seconds before it started convulsing

And it did not...We do allow for room air intake and there are provisions in our manuals for that, and tables showing required openings to rooms that do not provide enough free air or space. Clearly they saw a concentric and said I can do that! Same pipe is easy!

Nutjob

ChrisJ said:

> EGR
It helps cool peak combustion temperatures which allows a leaner mixture without knocking.

In vehicle exhaust systems this would be scavenging - moving exhaust flow from a small diameter pipe to a larger diameter. But what do I know? I'm not a plumber.

CapnCurt

Room air is often permitted with the appropriate room volume etc. But if the fundamental principle of a condensing boiler is to capture heat from flue gas condensate, it seems to me that the colder the intake air, the more efficient the condensate heat recovery would be... particularly if using a concentric flue arrangement. Thoughts?