GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Solar Water Behind a Window

calum_wilde | Posted in Mechanicals on

First a quick back story: I live in Halifax, Nova Scotia, which to my knowledge is zone 5…? I’m getting condensation on my cold water pipes, where the pipes first enter my house from my well. In another question about this issue, Charlie Sullivan was kind enough to offer a suggestion of using a drain water heat recovery unit to preheat the cold water. Which, really is a great suggestion as it’s 100% passive.

I took a close look at the applicability of this in my home and while it would be feasible, it would be cost prohibitive at about $700 for a 30 inch model and a couple of fittings to install it. Also, the hot water isn’t used very often, whereas the cold water is used quit often.

While I was looking at the situation and how I would need to plumb everything I realized that the water lines pass over top of a window that serves basically no purpose to the aesthetics of my house. It’s behind the HRV, in a utility closet, facing away from the road. So I thought, if I made a solar water heater panel to fit behind the glazing area of the window (30×30) it would likely be enough to raise the temperature of the water that few degrees I need to avoid the condensation. To make it out of PEX tubing, with isolation valves on the inlet and outlet, as well as a bypass valve, and a temperature gauge on the outlet, I’d need about $50-60 on top of the parts I already have.

So, if you’ve made it this far into my ridiculous idea, here comes a barrage of questions.

1) Would it work?

2) Would I have to worry about freezing in the winter? The room is in a finished basement that is heated in the winter.

3) Would I need to worry about over heating in the summer?

4) My cost estimate is without using any kind of aluminum fins. This was for a couple of reasons, first of course, was to limit cost. But also I don’t think I’d need that level of efficiency to prevent condensation, and I don’t think it would be desirable to have the cold water, which comes in at about 5-6 C, any more than say 10 C.

5) What am I missing? I’m sure there’s something. 🙂

Thanks guys.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. user-2310254 | | #1

    I'm not sure if it will work or not. But what would you do to keep the water warmer at night or doing an oh-so-sunny Nova Scotia winter day? Have you tried insulating the cold water lines? Are you concerned that sections of line in the walls are dripping? Are any of the lines in exterior walls?

  2. charlie_sullivan | | #2

    In addition to Steve's point about day vs. night, you'd have a small volume of water heated, so when you turned on the cold, you'd get a slug of warm water and then lots of cold water. My drainwater heat exchanger idea has the same problem, although the big ones have significant volume which can buffer it somewhat.

    But I think a better idea is a tempering tank--a simple uninsulated tank. It may sweat, but you can put a drip pan under it. If you locate it near the window you can think of it as a solar heater, but the location is not crticial--it's taking heat from the room and the window is contributing heat the the room, and they might or might not balance but it doesn't matter.

    It's a little hard to find pressure rated uninsulated tanks, but they can be found, for example

  3. calum_wilde | | #3

    Good point Steve. The humidity isn't an issue in the winter, my intention was to bypass the unit during the winter. My HRV is enough to get the humidity down to about 20% if I run it enough. During the summer though, when the HRV isn't able to reduce humidity, the humidity in the house gets to about 50%. I could run a dehumidifier, but I'd much prefer a passive solution.

    At night the kids aren't flushing the toilets every 20 minutes so the cold water usage is much lower.

    Yes, I have tried insulating the pipes, it only moves the problem further along. I have about 12 feet of room length before I can't reach the pipes enough to get the insulation on. I'm trying to avoid cutting into finished areas. Even if I could get insulation on to the pipes all the way along, it would only make the toilets sweat more than they do.

    None of the pipes are in exterior walls, thankfully. That'd I'd rip the drywall off for.


    My goal isn't to have continues warm water from the cold tap. More that the temperature of the cold line would normalize to room temperature as soon as possible when the usage is done. If the temperature of the pipe drops during a ten minute shower, and then increases again shortly there after, it should be enough to prevent the dripping.

    That said, thank you for the link, and both of these suggestions. I will certainly look into that aswell.

  4. user-2310254 | | #4

    If the toilets sweat, consider insulating the tanks. There are kits (apparently) and DIY options.

  5. calum_wilde | | #5

    Steve, the tanks are insulated.

  6. user-2310254 | | #6

    Calum. I think you need something like this:

    You can install it so most of the cold water flowing through your house is somewhat warmed. Of course, you may want to filter your drinking water or buy a Rheem Marathon, which has a plastic tank and no anode.

  7. GBA Editor
    Martin Holladay | | #7

    I agree with the other voices you have heard from. I don't really think that your idea is worth it.

    You are not the first person to think of installing a solar thermal collector behind a window. Marc Rosenbaum did it during the 1980s at his house in New Hampshire. However, he used real solar thermal collectors (without the glazing), and he mounted the collectors under sloped glazing in his sun space.

    Here is a link to an article that describes what Rosenbaum did: When Architecture Meets Energy Efficiency.

    I'll post a photo of his collectors below.

    (By the way, I'm not sure that Marc would try the same approach these days. My guess is that PV makes more sense than this type of solar thermal collector.)


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |