Preventing frozen pipes

Q: I have several questions about installing plumbing in a vacation cabin. I use my cabin on weekends only, including winter when temperatures are as low as -40­­° Celsius. I have a drilled well with a submersible pump and a septic system. A photovoltaic grid powers the water pump. How can I plumb the waste system to avoid freezing in the traps? Because the fixtures are close to each other, should I combine some traps? How should the water system be designed for easy and convenient drainage and startup on weekends?

A: Rex Cauldwell, master plumber and electrician in Copper Hill, Virginia, replies: Let’s tackle the drainage lines first. Except for the traps, there should be no water in the drainage lines to freeze. However, at low temperatures, water will freeze in drain lines as it flows through them. Ice will build up slowly and eventually block the lines. To counter this, drain lines must be buried below the frost line. Be sure to slope lines at least 1/4 in. per ft.

Plumb the system normally with one trap per fixture. The traps should be in a heated area to avoid freezing; otherwise, a vegetable-grade antifreeze will have to be added continually. Be sure to install traps with removable drain plugs. When you turn off the heat, open the drains.

For the water lines, use polybutylene, and be sure to install it properly: Make precise connections at the fittings, support the joints and allow the pipe to expand and contract. (For more on working with polybutylene pipe, see FHB #78, pp. 74-78.)

Polybutylene pipe is freeze-resistant but not freeze-proof. Instead of the normal 1/2-in. lines, install 3/4-in. lines, which drain better and freeze solid less quickly. For draining, install the pipe at a 1/4-in.-per-ft. slope, just like the drain lines, and do not put any loops in the lines. When I know the system is going to freeze, I normally attach each line to a board to eliminate low spots where water can pool.

Keep all lines out of outside walls. Even better, keep all lines out of all walls. Exposed lines aren’t just easier to repair; they also get more heat than lines buried in walls. Use the basement as the utility room and a home base for all the plumbing. Run the lines straight up from the basement, through the floor and into the fixture.

Use a drain at the water-pressure tank to drain the system. Install the water-pressure tank high enough so that a 5-gal. bucket can be placed under the drain. Make sure that all main valves are high-quality, full-port ball valves, which will allow water to flow freely as it drains. If possible, leave off all undersink turn-off valves, or stops, which also hamper the draining process. When you drain the system, be sure that you open all the fixtures.

If your photovoltaic system can supply the power, consider running 3w-per-ft. heat tape on the water lines, but not on the drain lines. Never heat tape a plastic drain line (the pipe might melt). Be sure to install a large pressure tank so that the pump doesn’t have to run often, which saves electricity, extends pump life and supplies extra water in case the electrical system fails.