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Basement drainage: has anyone ever insulated a drywell before?

richmass62 | Posted in Energy Efficiency and Durability on

I just added a new drain pipe to remove excess water from under the basement footing and from a rainwater tank to a garden near the street. See the attached pic, taken yesterday.

At the end of the pipe will be some crushed stone leading down to a drywell.

Question: has anyone ever insulated a drywell to keep it useful for more months out of the year? I have some reclaimed 3″ EPS foam I would like to use.

Details on the drain system, popup emitter for handling bursts of water, and drywell plans so far are here:

Feel free to post in that thread, which addresses the core issue: making a fieldstone basement more comfortable.

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  1. GBA Editor
    Martin Holladay | | #1

    It's certainly possible to use a horizontal layer of XPS to keep the frost from entering the soil, or to make the frost depth shallower. When a backhoe is digging a 4-foot deep trench for a water line, and hits ledge (bedrock) at 2 feet deep, this is the standard solution: install some 2-inch thick XPS on top of the pipe along the shallow section of the trench.

  2. richmass62 | | #2

    hi Martin -- FYI the foam I plan to use was obtained via Craigslist, it is of the EPS and not XPS variety ( I assume this could work and I was planning to also insulate the sides of the drywell, maybe the top three feet?

    While I have your attention, I am wondering if it would also be possible to use just six sheets of my surplus foam to superinsulate our current low-end (2010) 40 gallon electric water heater. Or would that be a fire hazard?

    I could build a simple box out of scrap 2 x 2 lumber to have something to screw to. Then surround it on all sides with nine inches of foam, overlapping and taping the sheets. The top of the box would have an opening, stuffed with 12 inches of fiberglass to allow in the water and electric line. A simple hatch would provide access to the shut off on the bottom. I could certainly use XPS on the bottom to better support the weight of the water.

    The electric bill is going up a lot in the winter, perhaps because the tank is in the basement. I don't really know what the tank's energy leakage is, but it seems to me that adding $72 (or even $96, for 12") worth of reclaimed foam would quickly pay for itself. But I have never heard of anyone doing this so I wanted to run it by the forum.

  3. GBA Editor
    Martin Holladay | | #3

    Yes, you can build an insulated box around your water heater. But be sure that you don't block the pressure/temperature relief valve -- it should be exposed, not behind an access panel, and it should have a pipe pointing downwards, open at the end. Also -- leave access to the temperature adjustment knob and the locations where the elements are attached, as well as the drain at the bottom.

  4. gusfhb | | #4

    Odds are you use more electricity cause the lights is on more.............they used to sell water heater blankets, yours would just be super duty

    as far as the drywell, if you just insulate above it it should stay thawed. frost line is 4 feet herabouts, how deep is it?

  5. richmass62 | | #5

    Martin -- I just might try this. I also have a Kill-a-Watt meter so it will be possible to measure electricity usage before and after to obtain data on whether it works.

    Keith - as for electricity usage, the lights alone can't account for the increase in the bill... all the bulbs are CFL. A more likely culprit is the blower for the enormous oversized gas furnace that unfortunately came with the house. They still sell those water heater blankets and I put one in when I was living in Somerville MA just a few years ago!

    Getting back to the drywell, the frost depth around here is also about 4 feet, but in his global warming-modified climate, I doubt the frost even reaches 3 feet down most winters. After thinking about this, I realize that a layer of ice on top of the popup emitter and a frozen intake path for the drywell are the biggest concerns. I'm going to have to figure out how to prevent the end of the french drain outlet pipe which is just 4 inches below grade, from freezing.

  6. davidmeiland | | #6

    I think I might invest some time and money in getting the water heater into the conditioned space. If you don't have room for a tank, and you have natural gas, maybe you're a candidate for a wall-mounted tankless water heater. I installed one in my place because of the space savings. For that matter, a tankless would do better than a tank in the cold basement because it's not sitting there losing heat.

    It takes more than a Kill-A-Watt meter to measure 240V usage at an electric water heater, or anything else that's not on a household plug... at least the ones I have.

  7. user-917907 | | #7

    The electric bill is going up a lot in the winter, perhaps because the tank is in the basement.

    Also, groundwater temperatures are coldest in the winter/spring. Air temperatures lag the solar season by about 6 weeks, and water/ground temperatures lag air temperatures by another 6 weeks.

  8. richmass62 | | #8

    thanks David -- I forgot that the water heater would be 240V. As for tankless, as far as I understand we could only go tankless for hot water for the showers, sinks, appliances. If we wanted to use hot water for radiant heating as well we couldn't just get a tankless system. On the other hand, if we go tankless there is a perfect place the burner to go. What kinds of intake./exhaust pipes are used with a tankless system... is this a direct vented appliance? If so the problem might be proximity to windows.

    Jack -- thanks for the info on the 6 week lag. (Peak warmth is supposed to be around July 20, I guess the lag in the norotheast is 4 weeks?This means that the basement floor temp would peak around September 6.

  9. GBA Editor
    Martin Holladay | | #9

    You can't use a 40-gallon electric water heater for in-floor radiant heat, especially if you are also using the water heater for domestic hot water, because the electric elements don't have much capacity.

    In any case, if you want to do space heating with electric resistance heat, why bother with a water heater and tubing? Just get some inexpensive electric baseboard units. (Not that I'm recommending that.)

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