Q. Dear Umbra,

We have an old storage tank water heater I’m afraid will go kaput any day now. What type of water heater do you think is best, climate-wise, to replace it? I don’t want to go crazy spending money, but it’d be nice to upgrade as greenly as possible.

Dominique F.
Philadelphia, Pennsylvania

A. Dearest Dominique,

I applaud you for thinking ahead: All too often, water heaters pick “dead of winter, when you have your in-laws visiting” to go kaput, and then your decision-making is limited to whatever’s in stock at the local home store. Doing your research now will lead you to the best intersection of green and affordable when the time comes.

Before I dive into my favorite options, a caveat or two: The ideal water heater for you will depend on your house, family size, fuel options (i.e., natural gas, propane, electricity), and other variables, so keep that in mind. Also, I’m no contractor — get the advice of a pro before you pull the trigger.

OK, Dominique, here are my picks for the eco-friendliest ways to get that water blazing hot, in descending order:

Solar water heater

Do you like the idea of harnessing the sun’s (free) rays and spinning them, Rumpelstiltskin-like, into golden energy? Me too. And that’s exactly what a solar hot water system does. Your own rooftop solar panel array magics the heat of sunbeams into your next hot shower, no carbon emissions necessary. OK, it’s not exactly magic; here’s how it really works. (Note: This type of system is separate from the solar array you might put on your roof to generate clean electricity.) Such a system saves about 2,400 pounds of carbon per year.

And yes, that performance is expensive — from about $4,000 up to $10,000, including installation. But hear me out, Dominique: You’ll get a 30 percent tax credit if you bite the bullet before the end of 2016. And you’ll be saving a chunk of cash on your energy bills. The time it takes for those savings to make up for the upfront cost varies widely (estimates range from 3 to 5 years all the way to 30 years), so you’ll have to crunch some personalized numbers to find out if this renewable upgrade counts as “crazy spending” for you.

Geothermal heat pump

If you can’t use the sun, then how about the earth? No matter what the weather is, anywhere in the world, dig about 10 feet down and you’ll hit a fairly constant 54-degree temperature zone. Geothermal heat-pump water heaters tap into this natural heat source via a system of buried pipes, then transfer that energy to your water. The pumps use some energy to operate, but it’s not much, and they’re generally quite energy-efficient and save lots of carbon. Geothermal water heaters are most often included in a whole-house heating/cooling system — quite a nifty setup, by the way, so if you’re also in the market for an HVAC makeover, this could be a match made in heaven.

This option is also on the spendy side, but it’ll save you money in operating costs and could pay for itself relatively quickly (one estimate for a whole-house system ranges from 4.7 to 15 years). And if you jump on it, you’ll also qualify for a tax credit.

Regular heat pump

These work like geothermal pumps, but instead of drawing power from the ground, they pull from the air. They’re not as efficient as their geothermal brethren, but they’re a big improvement over the status quo: Heat pumps use 60 percent less power than electric storage tanks. What’s more, they pay for themselves very quickly — within two years, if you get an Energy Star high-efficiency model.

Tankless water heater

One of the biggest drawbacks of the conventional storage water heater is that it’s constantly burning energy to keep hot water ready for your every whim. A tankless (AKA on-demand) heater sidesteps that problem by quickly firing up your water only when you need it, a trick that makes it up to 34 percent more energy-efficient than a storage tank (50 percent if you install more than one). They cost more than that tank, but less than my favorite options above — about $1,000 to $3,000. But they last 20 years or more, compared to more like 10 for that same old, same old.

Maybe someday we’ll figure out how to use the Earth’s molten core to heat both our water and our homes cheaply and efficiently. I, for one, will celebrate that day by building my own personal sauna. But ‘til then, happy water-heater shopping to you.

BTU-tifully,
Umbra