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Heat loss from floor drains to daylight

climb_on | Posted in Energy Efficiency and Durability on

We are in Minnesota (Zone 6a). 2200 sq/ft single level, slab on grade.

This question has been in the back of my mind for quite some time and I can’t find an explaination about heat loss from floor drains to daylight. I will heat our garage to about 45 degrees F, and have 2 floor drains that run to daylight. Seems to me that this will be not only a drain for water, but a drain for heat as well. Are there any stratagies for minimizing heat loss through the drain? We are not allowed by code to connect this to our septic system.

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  1. Robert Opaluch | | #1

    Hot air rises, cold air falls. So might not be as bad as you imagine. Cold air may not rise much through your drain, nor warmer garage air falling down the drain. Nobody ever mentions cold air dropping down through plumbing vents that go vertically through the roof. I always wondered about that...

    How long and deep is the drain? It is surrounded by earth so can absorb heat from the surrounding soil, also.

  2. onslow | | #2

    Try googling "floor drain trap seal" and review the images. There seem to be several choices of styles that are intended to prevent gas or varmint intrusion. I would certainly recommend a securely fastened slotted or grid cap at the air end of the pipe. I have a bizarre bunny that likes to nest in the one I didn't get to and my wife won't let me cap it now. At least it is not a rat.

    Putting in a J trap section for a garage drain might not be the best option unless you wash the car every week inside the garage (don't laugh, it has been done). The trap water will likely evaporate and in real life the water seal is good only against gases, not rats, as many New York apartment dwellers will attest. A trap also makes flushing the drain of salt and mud a bit more tricky. You would not want to ever connect to a septic system. Aside from gas issues, feeding your septic tank road salt and whatever else comes off your car could fatally affect the bacterial biome.

    As a side comment, plumbing vents do allow cold air to drop just like chimneys. Our old house in the midwest had an odd feature. The vent pipe penetrating the roof was a section of 4" pipe that made a 90 degree turn to connect to the main stack some 5' away. During some of the bitterest winters, the warm moist air in the stack would turn to frost inside the pipe near the turn. A few times enough formed to effectively plug the exit path which made flushing the toilets most exciting. Heating cast iron with a hairdryer is very tedious especially in an attic.

  3. Expert Member

    If your drains don't have a P trap you can add one anywhere along their length you can get access to. If you use them frequently you don't need to worry about them, but if they don't get regular use, pour a cup of mineral oil down the drain and it will keep the water from evaporating.

    Replacing the existing grill with one that screws down will stop the vermin that didn't mind a short swim from getting access.

  4. user-228058 | | #4

    What if you used a couple of infiltrator chambers and some crushed stone. This would allow the water to leach into the ground and prevent the air from coming in. Sort of it's own mini septic system

  5. climb_on | | #5

    Looks like there are some good possibilities with your search suggestion Roger, thank you!

    Im afraid a P Trap isn't a good solution with the sand and crap that will come in off the cars. One of these drains is in my detached shop and will have even more debris than the attached garage. My plumber didn't recommend the Ptrap, but couldn't speak to the air infiltration concern. I like the french drain idea, but it's likely to freeze solid in winter i think. I'll certainly add critter covers.

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