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Maybe I've had too long a day and misread something, but here I go anyhow. The efficiency of a gas water heater may be increased through mechanisms that enable it only when water flows through it, such as when one takes a shower or fills the dishwasher. In contrast, a classic electrically heated water tank sits there to be filled with cold water, which gets heated up, and if it isn't all draining out already, cools back down to require reheating. Reheating a standing tank of water several times over the course of a day is wasteful. In a related thread, also consider the same water tank while one takes a long shower. We've all* (* This is a vast generalization for the internet) had the hot water run out of us during a nice shower, and this is because an electric water heater cannot effectively heat a freshly filled tank of water while said tank is being drained. I'm sure if another person feels the need to expand on this at all, they're quite capable.

There are plenty of on demand water heaters in both gas and electric.

Combination Boilers that provide both hot water for heating and hot tap water are advancing quickly. Flexible PEX tubing these cut out a ton of traditional cutting and brazing plumbing labor to install hot water loops. It's also a lot more efficient to move hot water to a heat exchanger of some form in each room than to push air through ductwork. Some of these rigs also can be easily combined with a solar thermal roof array, further cutting your gas or electric costs.

I'm pretty excited about the last option, since I have an older house with poor air return paths, which means my furnace is almost always ingesting chilly basement air rather than getting a nice recirculation of heating air that's already been heated. Not to mention radient heat exchangers are silent and allow easy individual room temperature control with the smarter thermostat systems.

I recently moved into a house with the worst heating system ever: In ceiling radiant heating. Apparently the house was designed without regards to the laws of thermodynamics. On the upside, we have probably one of the warmest attics in the winter.

If I turn the heat on in all the rooms, I can watch the electric meter spin.

If you have access to the attic and it's unfinished, check if there's a reflective layer above the coils. If not, that's easy to add and will make a big difference.

Not this is a _reflective_ layer, not just insulation. The thermodynamics of radiant heat systems involve photon transmission, not just gas convection. If it was installed by a general contractor they may not have understood this distinction and the need for aluminum couplers and metalized reflective insulation.

Thanks for that tip, I'll try it. I actually reasearched it a bit more, and see that it is possible to have in-ceiling radiant that isn't crap, it's just that mine is crap. Supposedly it responds faster than forced air, but mine takes about an hour before I feel its effects. Also one room has 12' ceilings, which is stupid.

I just moved in to a house that has a gas on-demand hot water heater and I basically can't figure out why we use so much energy to keep gallons of hot water on hand all the time. It just doesn't make any sense to me. I think the upfront cost was higher, but the savings across the entire system are more than worth it.

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