10.7   Selecting Storage Water Heaters

Storage water heaters are the most common water heaters found in homes.

10.7.1   Determining a Storage Water Heater’s Insulation Level

Common storage water heaters consist of a tank, insulation sur­rounding the tank, and an outer shell. There is typically either 1 or 2 inches of insulation surrounding the tank. The insulation is either fiberglass or polyisocyanurate.

Follow this procedure to determine the water heater’s insulation level.

ü       Look for a listing of R-value on a label on the water heater.

ü       Find a hole in the outer shell where the flue pipes emerges or where plumbing connects. Look around the hole for either fiberglass or polyisocyanurate insulation.

ü       If the hole isn’t large enough to see the insulation level on an electric water heater, try removing the access panel for the heating element after disconnecting power from the unit.

ü       You may just be able to see the gap between the tank and outer shell. If you can’t see this gap, use a ruler or probe to push through the insulation along side of a pipe connect­ing to the tank until the probe hits the steel tank to deter­mine thickness. Make sure that the probe is against the tank and not against a nut welded to the tank.

ü       If additional tank insulation is installed, it must be at least R-11. Do not install insulation if the manufacturer’s label on the water heater prohibits it.

10.7.2   Storage Water-Heater Selection

Existing gas water heaters, including propane, typically use 200 to 400 therms per year. New gas water heaters use as little as 175 therms per year, resulting in a savings of between 25 and 225 therms per year. Similar savings are possible by replacing elec­tric water heaters. Consider the following recommendations for specifying water heaters.

•       A replacement gas or oil storage water heater should have an energy factor of at least 0.67 and be insulated with at least 2 inches of foam insulation.

•       A replacement electric water heater should have an energy factor of at least 0.93 and be insulated with at least 2.5 inches of foam insulation.