Some questions are easier to answer than others. For example, there is a fairly straightforward answer to, “How should I insulate the floor of my unconditioned attic?” — namely, “With a deep layer of cellulose.” (There’s more to say on the topic, of course — but even a full answer isn’t very complicated.)
There is no easy answer, however, to, “How should I heat my domestic hot water?” Every type of water heating technology is flawed; every solution involves compromise.
Many factors affect the decision about what type of water heater to choose, including:
The all-electric house
If your house has an unshaded south-facing roof, or a generously sized yard with room for a ground-mounted PV array, it’s a good guess that your house will eventually be equipped with a solar electric system — especially if your local utility offers favorable net-metering contracts to customers with PV systems. Since PV costs keep dropping, it’s hard to imagine that PV won’t play a significant role in our energy future.
As PV systems become increasingly common, energy experts predict that most U.S. homes will eventually be all-electric. Since burning fossil fuels contributes to global warming, environmentalists have been among the first to embrace the all-electric ideal.
In many states, net-metering contracts wipe out a customer’s electricity credits at the end of the year. That means that PV system owners who produce more electricity than they use are forced to donate their extra electricity to the grid. Instead of giving their electricity away, homeowners with large PV systems often swap their gas-fired water heater for an electric water heater. After all, for anyone who is subject to a “use it or lose it” net-metering contract, it makes economic sense…