Great topic!!! I've lived in Minnesota virtually all my life, & have seen all sorts of winters, driven through them, moved snow in them, etc & so forth. However, a couple years ago, in anticipation of my retirement, my wife & I moved into a double wide manufactured home on a lake. The second winter we were here the water line froze. The man that came out to take care of it for me put up with me following him around out in the cold & asking all sorts of questions, intending to get an education as well as a thawed water line.
What we had is an area under the house where the water line came out of the ground inside of a piece of 4"-6" PVC pipe with a heat tape wrapped around it. No insulation, no way of keeping track of the temp or whether it was really working. We figured that the heat tape had died, leaving the water line to freeze. I bought some fiberglass insulation & plastic sheeting, wrapped the former in the latter, and crawled under the house to encase the water line in the bundles of insulation. Then I bought two milk house heaters, one of which is still in the box, and put the other one inside the water line nest I had created. Happily there was already an electrical outlet down there. That got us through that winter with water flowing.
When spring came, I pulled out the insulation bundles and the heater, got some green treated 2X4's & 2X6's, along with some green treated 3/8" plywood, stiff foam insulation, construction adhesive & a few cans of The Right Stuff spray insulation, and got to work. I created a wall all the way around where the water line came out of the ground over to where it went up into the house. This space also enclosed a sump pump that had been put in place to pump ground water out of the area. I trashed that & my wife & I dug in a sump pit outside of the wall of the house for a sump pit, rock, etc. The wall was then insulated, spray foam sprayed in all the nooks & crannies, and when last fall came around, two trouble lights were plugged into the electric strip in the space. One of them was plugged into a Woods # 32555WD remote control outlet. I also installed a temp sensor for an electronic temp display unit, and a month ago when it got down to -35, I put the milk house heater in the space with a remote control outlet for that too.
I am currently sitting on the edge of my bed, typing this reply, looking at the temp display, which shows 10 degrees F outside, 55 degrees F in the water line nest, and 66 degrees F in my room. Two trouble lights with a 75 watt bulb in each are currently on in the nest, as earlier last night the nest temp fell to 40 degrees F. I like to keep it between 45 & 55 or higher. When it got down to -35 earlier, I woke up at one point & saw on the temp display that the nest was at +101 degrees F, so I went out & adjusted the temp control on the heater. It is a 1500/750 watt heater, set currently on 750 watts with the temp control a bit under halfway to the max setting. So far I have only used the heater if it gets below -10 degrees F or so. It is not currently on. So for the cost of running two 75 watt light bulbs I have the nest at 55 degrees F with an outside temp of 10 degrees F. If I want to know for sure if a light is on or the heater is working, I can open up the nest & see that at a glance, unlike a heat tape.
When it gets really windy, I can tell by the temp display, so come spring I need to find & plug some air holes. I think that's coming up under the bottom of the siding, just in case you run into it. But all in all it's been big fun, my first big project after retirement, all controlled on the top of my coffee table by a couple small remotes & a temp display!!! Obviously one could set the same sort of thing up with a thermostat. Others have cut a hole from the house into the same kind of space & counted on the house heat to keep it warm. I like my setup because it's pretty precise, and I know the temp in the nest at a glance. Um, I still can't wait for spring................
