Tankless Water
Heaters & Unheated

Tankless Installed in Unheated Buildings or Exteriors -
 A Bad Choice for Vashon

After examining several different out building designs on the island where the water heaters or related piping had frozen it's become clear that a tankless water heater was not a good choice. With a tankless heater there are three installation options:

1. a direct vent which means a second flue pipe to the unit that draws combustion air from the exterior.
2. installing two openings to the exterior, one close to the floor and one near ceiling height
3. construct an out building that is 30 ft x 30 ft x 8 ft high i.e. 7,000 cubic feet

The direct vent option is probably the best of the three options. However even with a direct vent there is loss of heat to the outdoors and more importantly, the volume of water in the unit itself is very low and so when it cools down for long enough it easily turns to ice. Solution:
What I have seen time and time again is that standard tank type water heaters, whether they're gas or electric don't freeze even during power outages. Now I may have missed a few electric water heaters out there that have frozen but the ones I've seen haven't. I believe the reasons for this are that the volume of water in the tanks hold heat long enough to withstand any outages and the volume itself keeps the water from freezing. Also with an electric tank you don't need any openings to the exterior for combustion since there is no combustion so the ambient heat stays in the room. The gas water tanks need combustion openings to the exterior however during a power outage the gas stays on. They don't require any electrical power so the water stays warm throughout. The additional advantage here is that you have hot water no matter how long a power outage lasts.