How Efficient Is Your Water Heater?

[Dr. Shane]

"Next to heating or cooling, water heating is typically the largest energy user in the home. As homes have become more and more energy efficient during the past 20 years, the fraction of energy used for water heating has steadily increased."

Consumer Guide to Home Energy Savings

Quote:

The most efficient gas-fired storage water heaters have energy factors ranging from 0.60 to 0.65, corresponding to estimated gas use below 250 therms/year. Condensing water heaters have energy factors as high as 0.86. The most efficient electric storage water heaters have energy factors ranging between 0.93 and 0.95, resulting in estimated annual energy use below 4,725 kWh/year. There is little difference between the most efficient electric resistance storage water heaters and the minimum efficiency standard.

We have an electric water heater. We bought it about seven years ago so it probably only has a few more years left. I think I will replace it with a propane one but have not decided if I want to stay with the tank or go tankless.

[Amelia]

Im not sure about mine as I live in an apt. But if I ever have a house again, I would love to have those continuous-flow,on demand water heaters like they have in the UK. No maintaining hot water in a tank. No cold water waste waiting for the hot water to arrive.

[Dr. Shane]

Continuous-flow and tankless are different terms for the same thing. They cost between $600 and $1000 and have to be either natural gas or propane. That is if it is going to heat all the water for the entire house. They do have problem keeping up with multiple demands - if two people are both taking showers in different bathrooms in the house or a dishwasher is running.

Point-of-use water heaters can be electric. Those are mounted under each sink and at the shower. They work well for the shower but not for a bath. We have one point-of-use heater I bought for the shower out at our pool.

[bevin]

Efficiency of propane v electricity: Remember that the electricity has to be produced somewhere and transmitted to your house. The efficiency rating only reflects what happens inside the heater - and hence does not measure the same thing as propane efficiency rating. In both cases, just calculate the actual cost of the heat - don't worry about environmental issues

Tank v tankless: Remember also that there are reliability/replacement costs involved - which may depend on the acidity and purity of your water.

It is pointless to pay more for a "more efficient" system if you don't recover the costs in the lifetime of the unit. And when you are calculating the costs, don't forget the lost interest income on the extra money you spend.

For instance: Which of the following should you buy if you are getting 5% return on your invested capital?

High efficiency unit A costs $200, and

has expected lifetime of 10 years, and

costs $40 per year to run

Low efficient unit B costs $100, and

has expected lifetime of 20 years, and

costs $50 per year to run

The easiest way to do this stuff is to model it with a spreadsheet - and the results are often surprising.

After 10 years, when the high efficiency unit needs to be replaced, you are down about $503. The low efficiency unit you would be down about $466! The lower initial cost and the interest on the money has more than paid for the higher bills AND you still don't have to replace the unit for another 10 years!

After 20 years, high efficiency you are down $1620, low efficiency you are down $1387.

Scary, isn't it! These decisions are not as easy as they seem

/Bevin

[Neil D]

Another way to lower your costs, Shane, is to pre-heat your water with Solar. Granted, it involves another storage for water being warmed but it can significantly reduce costs. For example, a solar panel placed on the roof can heat water in an old water heater, which is preheated, and drawn from that tank. The solar tank may not be at a temperature for a shower, but it can be raised from a cold of 65 degress to 85 degrees, thus making your hot water tank less expensive to maintain... just a thought

[Amelia]

Shane, you live in a great place for solar use.

[GreatLakesGramma]

We have a high-efficiency power-vented gas water heater. It was propane when we got it, 14 years ago, but we switched to natural gas 10 years ago, and had it converted. The only problem with the power-vented feature is that if the power goes off, it won't heat the water, because the burner won't come on if the vent won't run. But we have our own well anyway, so if the power is off we can't pump water, so we use as little as possible until the power comes back on.

I'd really like to get a wind generator. The wind is almost always blowing here, so it would almost always be working.

[nuff sed]

Many years ago my academy roommate had a house powered by a wind generator. If my memory serves me correctly, the storage batteries were very costly. He finally got them surplus from a telephone company that was upgrading. Regards, Don