Turning sunlight into hot showers: best kits or hacks?

I get where you’re coming from about critters - mice can squeeze through gaps you’d swear were too small for anything but air. But I think there’s a bit more nuance to the venting question, especially when it comes to solar hot water setups. If you’re using something like polyiso or XPS foam, sure, closed-cell is great for keeping out both moisture and pests. But with natural insulation (wool, cotton, even some recycled denim), trapped moisture can really wreck the R-value over time and lead to mold. That’s a different headache altogether.

I’ve seen a few DIY solar water heater builds where people use a “rain screen” approach - basically, they create a ventilated cavity behind the insulation, but then wrap the whole thing in a fine mesh or hardware cloth. It’s not totally critter-proof, but it does cut down on the risk a lot. You still get airflow to dry things out, but you’re not just leaving an open invitation for every mouse in the neighborhood.

One thing I learned the hard way: condensation can be sneaky. I once insulated a batch solar collector with fiberglass and skipped venting, thinking I’d sealed it up tight. By the end of the season, the inside was damp and musty, and the insulation had slumped down. Ended up having to rip it all out and start over. If I’d added even a little passive venting - maybe just a couple of screened holes at the top and bottom - I probably could’ve avoided the mess.

Closed-cell spray foam is definitely a solid option if you’re not worried about off-gassing or cost, but it’s not always practical for every project. Sometimes a hybrid approach works best: use foam where you can, and vented natural insulation elsewhere, but always with some kind of barrier to keep the wildlife out. It’s a balancing act, for sure.

Venting’s important, no doubt, but I’ve had issues with the “rain screen” method in really humid climates. Sometimes that extra airflow just brings in more damp air, and it never fully dries out. I actually had better luck sealing everything up tight and using rigid foam, even if it meant dealing with the cost. Less fuss over time, less maintenance. Guess it depends on your local weather and how much you want to tinker later.

Yeah, I hear you on the rain screen thing. Down here, the humidity just hangs in the air, so all that venting sometimes feels like it’s just inviting more moisture in. I ended up sealing up tight too, with rigid foam and a ton of caulk. It’s not cheap, but honestly, I’d rather pay up front than deal with rot or mold later. Maintenance is way less of a headache now. Guess it’s one of those “know your climate” deals - what works in one spot can be a total pain somewhere else.

I get what you mean about sealing things up - humidity’s a beast where I am too, and I’ve definitely fought my share of mold. Switching gears a bit, have you tried any solar water heating setups in your climate? I’ve been eyeing those DIY kits with the black hose coils, but I’m not sure how well they’d hold up with all the moisture and heat. Wondering if anyone’s had luck making one that doesn’t just turn into a science experiment after a few months...

I tried the black hose coil thing last summer, and let’s just say it turned into a hot mess - literally. The water got scalding mid-afternoon, but the hoses started to get slimy inside after a couple months. Maybe it was all the humidity? I ended up scrubbing them out more than I actually used the hot water. Has anyone managed to keep those things clean long-term, or is there some trick I missed? I keep wondering if switching to copper pipe would help, or if that’s just overkill for backyard showers...