[RE-wrenches] Modules over vents

[Bill Loesch]

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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