A New Generation of Demand Water Heaters

Demand (or instantaneous) water heaters have always had the advantage of eliminating standby heat loss—instead of storing hot water in an insulated tank, the water is heated at the point of use. You only heat the water you actually use, so significant savings can be achieved. The problem with demand water heaters has always been that either they are electric (requiring very high amperage and converting only a third of the primary energy into useable thermal energy) or, if gas-fired, they had continuously burning pilot lights that wasted a lot of energy. When storage-type water heaters have pilot lights, at least the heat from the pilot—typically 300 to 350 Btus/hour (88 to 103 watts)—ends up heating the water, offsetting some of the standby losses. When demand water heaters have pilot lights, the energy is simply wasted, with typical losses of 3 million Btus or 30 therms per year (900 kWh/yr). The result is significantly depressed Energy Factor ratings, in spite of high combustion efficiency (see discussion below). Now gas-fired demand water heaters without continuously burning pilots are beginning to appear in North America. We profile two such products here, from manufacturers who have taken very different approaches to eliminating the pilot.

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