Bath fan under solar panel

[candyR]

Hello,

We're considering a grid-tied solar panel installation - will likely be 16x Sunpower 327W panels on our roughly South-facing roof.

Our bath/shower fan vents on the roof with a small cap (appears to be a broan 636 or 634) that sticks out a few inches over the roof shingles. Is it OK for the solar panels to cover the vent? Will the vent still work OK? The installer thinks so.

Sorry if I missed a thread - I found a few threads related to sewer/plumbing vents, but not about bath vents (threads that started with both ended up focused on the sewer vents). FYI, our sewer/plumbing vents are at the lower corners of the south-facing roof and will be left as-is (I guess they will cast some shadow on a couple panels).

Thank you for your help.
--
Candy

[Naptown]

The vent will work fine.
Issues come when you are exhausting large amounts of moisture when the temperatures outside are cold.
If you are like most people you don't run the fan in the winter to exhaust the moisture from the bathroom but use it as a humidifier.
Not much of a problem in that case.

[J.P.M.]

The vent will work fine.
Issues come when you are exhausting large amounts of moisture when the temperatures outside are cold.
If you are like most people you don't run the fan in the winter to exhaust the moisture from the bathroom but use it as a humidifier.
Not much of a problem in that case.

1.) Some building codes may not allow covering a vent. I'd check on that.

2.) If I was an installer, and that vent slowed me down, I'd be tempted to say the same thing.

3.) IMO, based on my experience w/ bathroom vents in a cold climate is that (counterintuitively) they don't do as much to humidify the house as I initially thought. More importantly, the moisture in the bathroom air, while it may have some (I stress) small effect on humidification for the rest of the dwelling, can cause longer term problems w/mold growth, smells and other problems when the excess water vapor sort of shock loads the room air with moisture that diffuses through the bathroom walls and window frames (where surfaces are supposed to, but don't quite, meet) and condenses on colder surfaces including inside insulation. For a lot of reasons, I'd respectfully suggest that venting moist air from kitchens and baths is more important in cold weather than warm weather to avoid problems that build up over time. You lose the warm air that's exhausted, which you pay for, and that's a PITA especially considering you're trying to button up the house to reduce infiltration (and BTW decrease the need for artificial humidification), but cut down on the probability of mold and dry rot induced structural and health problems that take years to accumulate and tend to be very costly in many ways besides, and in addition to, financial. I always considered venting a necessary evil. For carpet shocks, dry skin and creaky furniture, get a central humidifier for the furnace. Not venting the bathroom air may result in the house tending to eventually smell like the soap and shampoo you're using along around valentine's day.

4.) As for not using the fan, I'd assume that a bathroom vent, unless it's disconnected, will always be used. If so, moisture, heat and probably bacteria may wind up on the underside of one or more panels perhaps causing unforeseen problems. If it were me, I'd try to avoid that.

5.) Some things to perhaps consider: Raise the array from the roof by 6"- 8" or so if allowed by building code/HOA. This will perhaps allow more circulation under the array and reduce moisture effects some. They may also run a bit cooler as a bonus. Aesthetics may be a concern however. Second, duct the vent penetration once it gets outside uphill beneath the array. Another possibility is to move the vent to a wall. This will cost more but if possible will kill the interference problem on the roof and probably result in better venting that will also avoid the problem of condensation that running a vent through uninsulated attics on the way to the roof can lead to, if it hasn't already.

6.) Doing nothing IMHO, does not seem like a good, long term solution. Solar's great stuff, but not at the expense of short circuiting other systems in the house. Bathroom vents are there for a reason.

[russ]

In new construction an ERV/HRV (energy or heat recovery ventilation) unit works great at expelling humidity while saving most of the heat - many are really quite efficient.

[candyR]

We do use the fan mostly in winter. We get a lot of condensation in the bath/shower without it (and some with it on too), so I am concerned about mold etc if we don't use the fan [Yes, it hurts to have to dump moisture and heat out]. In summer, the window is open, so there's less need for ventilation.

I had hoped the solar panels could handle the moisture as they are built to take on the elements. Is that not the case with the underside?

I'll check on how high the installer intends to put the panels too.

[Naptown]

If it is in use it may be best to move it to a side wall or near the plumbing vents to get it out from under the panels.

[J.P.M.]

If it is in use it may be best to move it to a side wall or near the plumbing vents to get it out from under the panels.

I'd suggest bearing in mind not to run the ducting "downhill" if going to the plumbing vents which sound like they might be at a lower elevation than the existing exhaust vent penetration. Just a thought.

One other thing: Often, the underside of most panels are considered to be somewhat, but by no means completely protected from the elements, particularly most moisture. I'd question the robustness of some under panel electronics to withstand a cyclic, daily onslaught of moisture and other stuff from a bathroom. I bet that sort of thing wasn't a big part of the design criteria.