>Not to mention that gas heaters are simply more efficient for heating to begin with.
Are you sure about that? A heat pump with a COP of, say, 2 is 300% efficient (it is said to have an Energy Factor, EF, of 3). That is, for every Joule of electrical energy supplied to the pump, 3 Joules are added to the water tank. On the other hand, the combustion products of a natural gas heater need to be exhausted outside the building. Unless they are first cooled to the temperature outside, the heater is less than 100% efficient.
Where I live, a Joule from the electric company costs about 2.5 to 3 times as much as a Joule from the gas company. A quick Google search indicates that this type of water heater typically has an EF of 2 to 2.5. The cheapest gas heater I could find on the Home Depot website was over $300 (twice your Mexican one) with an EF of 0.62. So it wouldn't surprise me if the energy cost of an electric is on par with the energy cost of a gas heater, and it would surprise me if the electric actually used more energy. I don't see how you would save thousands of dollars in energy with a gas heater: Even in the worst case (a 2 EF electric heat pump vs. a 0.62 EF gas in a location with a 3x energy cost ratio), the gas only just breaks even.
Market effects affect to the economic perspective, but considering the transformation of fuel to heat, gas is sure to be more efficient. Electricity used to run the heater is generated by burning something and running a turbine - a process that itself runs with around 30% efficiency. Add to that the power loss from electricity distribution. 300% efficiency on the heater isn't enough to break even so that you'd get as much heat from the same amount of gas burned locally versus in a power plant.
Well, ok, so 30% thermal efficiency at the power station[1], and 10% loss in the transmission lines[2]? That gives us .3 * .9 * 2.5 = .68, or 68% thermal efficiency. That compares favorably to the manufacturer-claimed 62% efficiency of the gas heater I cited above. I can even imagine a scenario where an architect could design a house so that heat source of the water heater is near the heat sink of the fridge. In that case, the coefficient of performance of both devices would improve.
In case this wasn't obvious before, let me state this very clearly: Over 30% of the energy content of the natural gas used by your water heater goes up the chimney and is not used to heat the water. Gas water heaters and furnaces are NOT 100% efficient.
[1] Wikipedia claims that conventional external combustion (i.e., steam) power plants have a thermal efficiency of 33%.
[2] Wikipedia claims that transmission and distribution losses nationally averaged 6-7% in recent years.
This is neither here nor there, but it strikes me as interesting that the most efficient energy management in a home is just ensuring that your interior environment stays stable and isolated from the exterior as much as possible.
Okay, you got me. Still, burning stuff locally is in the same ballpark as running a heat pump with the electricity. Should microturbines become feasible to buy and operate in every home, it would be the most efficient way, running a heat pump by a turbine of your own and using the waste energy as heat source as well.
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.
>Not to mention that gas heaters are simply more efficient for heating to begin with.
Are you sure about that? A heat pump with a COP of, say, 2 is 300% efficient (it is said to have an Energy Factor, EF, of 3). That is, for every Joule of electrical energy supplied to the pump, 3 Joules are added to the water tank. On the other hand, the combustion products of a natural gas heater need to be exhausted outside the building. Unless they are first cooled to the temperature outside, the heater is less than 100% efficient.
Where I live, a Joule from the electric company costs about 2.5 to 3 times as much as a Joule from the gas company. A quick Google search indicates that this type of water heater typically has an EF of 2 to 2.5. The cheapest gas heater I could find on the Home Depot website was over $300 (twice your Mexican one) with an EF of 0.62. So it wouldn't surprise me if the energy cost of an electric is on par with the energy cost of a gas heater, and it would surprise me if the electric actually used more energy. I don't see how you would save thousands of dollars in energy with a gas heater: Even in the worst case (a 2 EF electric heat pump vs. a 0.62 EF gas in a location with a 3x energy cost ratio), the gas only just breaks even.