[RE-wrenches] Modules over vents

Wed Sep 24 07:33:57 PDT 2014

I just finished installing an exhaust vent/intake pipe for a NG powered
demand water heater in rental property I own. The manufacturers instructions
require the vent to be a minimum of 12 inches above the roof. 

If you added another 6" of PV you could potentially disrupt the flow of
exhaust and likely violate its UL listing. The 'pipe' trade name is "3X5", 3
inch diameter exhaust pipe inside a 5 inch galv pipe. 

If needed you could buy a 6" extension to maintain the clearance but the
shading would still be a problem.

Jim Duncan

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Bill Loesch
Sent: Wednesday, September 24, 2014 5:38 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Modules over vents

Bruce, August, et al,

This is but one more example of confusing terminology. A plumbing vent is
not an exhaust vent!

A plumbing vent (what August calls a cold vent) is provided to allow the
sanitary drain traps (and perhaps more) to operate properly. Without the
properly functioning traps you would have sewer gas smell and sewer gas from
the plumbing fixtures. This was commonplace when indoor plumbing was
introduced to early adopters.

An exhaust vent is another animal entirely. An exhaust vent carries the
combustion products to a suitable exterior location for dilution with
ambient air. With the advent of power vented combustion appliances, a direct
vent (one that takes in combustion air from the outside and naturally
exhausts combustion products to the outside) is IMHO the only responsible
way to install any power vented appliance in a freezing climate. (Power
vented appliances come in both condensing and non-condensing flavors-they
can penetrate the side wall or the roof). Originally, two separate pipes
(with two independent properly separated penetrations) was used. That
technique is still often used today. More recently concentric vents have
been introduced both for condensing and non-condensing applications. A
concentric vent can simplify some installations by putting the exhaust pipe
inside a larger air intake pipe allowing for one, albeit larger,
penetration. As you might imagine if the exhaust flow is
hindered/diverted/redirected by an inappropriately located solar module
combustion gasses will be re-ingested into the intake air. Not good for
equipment performance. My understanding is the power vented appliance
manufacturer dictates what kind of separation/clearances are needed with
their product. My guess is you find they want at least a foot of separation
between the top of the " inverted cone" and the module. Probably not what
you had in mind for an aesthetically pleasing installation.

I hope this helps,

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094

On 23-Sep-14 6:54 PM, August Goers wrote:

Bruce and All,

Sorry, I hit send before I had a chance to complete my thoughts. What I
meant to say was that I've found AHJs often allow us to cover cold
plumbing vents but I've never tried or had any luck with covering hot
vents including condensing boiler PVC vents. Once again, if in doubt you
could see what the plan checker or inspector thinks.

Best,

August

-----Original Message-----
From: August Goers [mailto:august at luminalt.com]
Sent: Tuesday, September 23, 2014 4:15 PM
To: 'RE-wrenches'
Subject: RE: [RE-wrenches] Modules over vents

Bruce,

I'll send you the CA plumbing code vent section offlist (attachment too
large for this list). The way I read the code is that you technically
can't cover any type of plumbing or hot vent. However, and I've run into
little resistance from AHJs in the Bay Area by covering these. You might
want to check in with your plan checker.

Best,

August

Luminalt

-----Original Message-----
From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Bruce Leininger
Sent: Tuesday, September 23, 2014 3:49 PM
To: RE-wrenches
Subject: [RE-wrenches] Modules over vents

Hi all.  We're designing a system on a roof that is literally infested
with plumbing, exhaust and combustion vents.  The combustion vents are PVC
and none of the vents are more than 1.5' above the roof.

A racking company says that we can cover them with modules, since the
modules will be at least 4' above the roof.  They have not yet provided
any building code references to say that this is ok.  Do any of you know
if the building code allows this?

Thanks.

Bruce
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