Heating a cold crawl space with indoor air via duct fan?

[Jonatan79]

Incoming water, the black hose has a heating cable, but the water hoses between the toilet and kitchen inside the insulation don't have a heating cable and it's difficult to fit one afterwards.

Has it frozen or are you afraid it will?

 

[norddal]

Is it the first year you have water? Or how have you done in previous years?

If there's no way to insert a heating coil, that's obviously the best solution, but isn't there an access hatch or something so you can get under the house? Otherwise, it's not a crawl space

True, right now it's not a crawl space but I'm prepared to make a hatch, second year with piped water and have managed so far without freezing.

 

[norddal]

Has it frozen or are you afraid of it?

Not frozen yet, but the wireless thermometer under the house (it wasn't a crawl space) last showed 0 degrees, so freezing doesn't seem unlikely.

 

[norddal]

It's normal physics. If you blow warm air into a cold space, you may potentially get condensation because the warm air can carry more moisture. It can be done safely, but you need to have a very good grasp on the parameters (dew point and RH) in the spaces and stop the fan under unfavorable operating conditions. It's quite tricky to do. Hence the recommendation to instead just heat the existing air in the crawl space.

If you can't access the crawl space in a good way, you should start by solving that problem. Sooner or later, you'll have a pipe that freezes, and then you'll need to gain access.

Okay, I understand. I see many here write that sending down heat is a bad idea. Maybe one should also focus on better insulating the foundation from the outside. If I hadn't been shoveling snow around the foundation, it probably would have already frozen.

 

[tommib]

You might possibly send down heat, but not moisture (in the form of water vapor in hot air). If you absolutely can't go down and want a fan that blows air there, it's better to use a duct fan that draws air from outside and heats it with an electric heating element in the duct. This is also a solution that must be controlled so you don't send down outdoor air when it is warmer than the crawl space (or, well, when there is a risk of condensation, but that's a lot more complicated to calculate).

Hopefully, you have a hygrometer on your wireless thermometer down there. By the way, how did you get it down there?

 

[Jonatan79]

You might be able to mount/partially bury insulation of the type thick styrofoam around the exterior foundation in the fall/winter?

 

[Mikael_L]

And one more thing, norddal.
It doesn't really reduce heating costs to first heat the air inside the house and then send it down to the foundation; you might as well heat directly in the foundation with a frost guard, and then save a few kWh each winter.

 

[norddal]

You can send down heat, but not moisture (in the form of water vapor in warm air). If you absolutely can't get down there and want a fan that blows air down, it's better to use a duct fan that draws air from outside and heats it up with an electric heating element in the duct. This is also a solution that needs to be controlled so that you don't send down outdoor air when it's warmer than the crawl space (or rather, when there's a risk of condensation, but calculating that is much more complicated).

Hopefully, you have a hygrometer on your wireless thermometer down there. By the way, how did you get it down there?

Yes, it seems to be a bit of a science. I got the thermometer in through the ground vent, thought it was also a hygrometer but it's not. I haven't found a wireless one.