Expert: Daniel Humphrey - 11/17/2008

Question
QUESTION: My pex water pipes have to travel about 3 feet in the crawl space up into the house. I haven't got electric for a heat tape. What can be done to protect it from freezing? Can it be insulated adequately even though the water can only be pumped when the sun(solar) is out and the pressure tank is not large enough to allow a trickle for very long? It can get to 35 below zero here.

ANSWER: Dear Bern,

The key is to identify (or create) the source of heat, expose the pex to that source, and then insulate the chamber.

In my area, the ground is 42 degrees F; if I build a box between the ground (digging down a foot or so into the earth) and floor and then insulate around the sides, the pipes will not freeze.

If the ground beneath the house is already frozen or permafrost, you'll need to bring heat from the house into that area. Because the "hatchway" coming up from the floor is the low spot, the cold air will naturally pool there (rather than the warm air you desire), or cold air will be drawn past the tubing as a result of the house's chimney effect. For this reason, such an arrangement requires an airtight chamber so that no outside air can enter. To keep the cold air from pooling there, the chamber must be fairly large to allow air flow around the tubing.

Hope you can work this out.

Daniel

---------- FOLLOW-UP ----------

QUESTION: Hi Daniel
What I'm wondering is, How do you find out what the winter temperature of your ground is? And did you mean insulate inside the box or outside of it? Or both? Would you leave an airspace around the tubing? Of what size,if so?/ Bern

Answer
Bern,

The ground temperature is normally the temperature of the cold tap water that runs underground. If you have a well nearby or a town, you can take the temperature of that water. Another way is to dig down about four feet and bury a thermometer probe.

The boxes I make for carrying tubing are made from treated plywood, about 24" square on the outside, and framed with 2x4 blocks so that another plywood box can fit inside, with insulation in between. This inside box is about 16" suare, with plenty of air space to keep the warmer air circulating. All the joints are caulked to keep cold air out.

Daniel