It’s not something we deal with often, but freezing temperatures in Charleston can wreak havoc on our plumbing. Our common solution for protecting our water pipes is to leave a sink or two dripping overnight, but one device is especially susceptible to this unusually cold weather: the tankless water heater, particularly when mounted on the exterior of the home. While in more northern climates the tankless water heater is nearly always mounted indoors to shield from the predictable subzero temperatures, the temperate climate of the South Carolina Lowcountry allows for outdoor mounting to be more common.
Exterior mounting has its advantages and is typically without incident, but a particularly cold winter snap calls for some caution to be had to protect tankless water heaters from suffering damage. Most modern tankless water heaters have built-in freeze protection for those cold winter days, but this is a short-term system that protects only the unit itself, not the plumbing outside. Take precautions to ensure that your hot water keeps flowing when you need it most.
Insulate the Water Pipes
To prevent the water lines that lead into the tankless heater from freezing, the pipes should be properly insulated. Measure the length of the outdoor water lines that are vulnerable to freezing, including those running along the inside of exterior walls and those in uninsulated basement areas. Apply a self-sealing pipe wrap to the water lines; they are typically made of rubber, polyethylene, or fiberglass.
In addition to passive insulation, an electric heater cable can be added to the water lines to ensure they won’t be damaged by freezing temperatures. Plug into the nearest electrical outlet, and run the cable along the pipe with a twist in the cable every 12 inches to make a spiral pattern along the pipe. Secure the heater cable to the pipe every few inches with the electrical tape, not allowing the heater cable to cross itself along the pipe. Finish by wrapping the pipe in a tight spiral pattern with insulated tape, overlapping each turn by about a quarter-inch so that the pipe is completely covered.
Drain the System
Are you planning to ride out the winter months in the Keys? If your home is unoccupied for extended periods, tankless water heaters should be drained ahead of the season to prevent damage. For this winterization you will want to consult the manufacturer guidelines or have it performed by a professional.
For the less patient, it goes something like this: Shut off the gas or electric supply and let the water in the system cool. Shut off the water supply and then open the taps to release pressure. Disconnect both the incoming and outgoing pipes from the tankless heater, and also remove the inlet water filter (have a bucket handy) – make sure all the residual water drains from the system.