Buildings

Energy Efficient Water Heater

Q: We're planning our new house, and need to decide on what kind of water heater to get. We're building a very energy efficient house, and I read somewhere that heating water is the biggest energy user after heating & cooling. We're thinking about a tankless heater, although my cousin Fred says solar is the only way to go. My brother says gas is much cheaper than electric, but my neighbor says they're about the same. The more I look into it, the more confused I get.

A: So many questions, so little space. You are certainly correct about the water heater being a major energy user in the typical home. You've already told me you're not building a "typical" home — you're planning an energy efficient home. So what do you need to do to get an energy efficient water heater to go with it?

First of all, look at your expected hot water use. How many people are in your household? Any children? Teenagers? Obsessive hand washers? How often will you have overnight guests? Based on a number of new homes I've been in lately, a fair chunk of the population is into recreational bathing — tubs big enough for 2 or 6 people in a bathroom big enough to entertain the whole bowling team. Are you planning a basic bathing facility, or do you picture soaking in the whirlpool for an hour every night?

You need to distinguish between your ongoing needs and occasional needs. If you have a houseful of guests twice a year, do you want to pay for heating 80 gallons of water every day, or would you rather deal with the inconvenience of staggered showers twice a year? Most people probably have much bigger tanks than they actually need. Figure out the most you'll realistically need in one hour and compare that to the First Hour Rating of different models.

Tankless water heaters can save some money, but only in some circumstances. One advantage is that you don't have a full tank of water sitting there losing heat while waiting to be used. If you buy a new, energy efficient water heater, it will be well-insulated and the standby losses are not great, particularly with an electric model. Gas models do have a flue going up through the middle of the tank which increases the standby losses.

The other big advantage of a tankless heater is that you have, essentially, an endless supply of hot water. This will carry you through nicely when you have houseguests. On the other hand, if you have teenagers in the house, an endless amount of hot water available often translates into The Endless Shower. Savings from eliminating standby losses can disappear pretty quickly with someone taking 20 or 30 minute showers.

Most people think in terms of either electric or gas. Natural gas is the lowest cost water heating fuel in most parts of the country, but don't get trapped into thinking that propane, or LP gas is similarly cheap. Your brother and neighbor may both be right. If your brother has natural gas, it's probably considerably less expensive than electricity for heating water. Your neighbor, on the other hand, may not have natural gas available, and may be using bottled gas (LP, Propane). LP prices seem to fluctuate a lot, and in recent years have at times climbed above the price of electricity in some areas.

Solar water heating is definitely the lowest cost option, particularly in states like North Carolina which has a 40% tax credit on the cost of the system. A typical solar water heating system will supply more than 50% of a household's hot water over the course of a year. The initial cost is high, but the operating cost is low.

Another consideration is the health and safety aspect. Combustion systems need to be installed so that combustion by-products such as carbon monoxide cannot enter your living space. Specify only sealed combustion or power-vented units, or install the unit totally outside the living space. This can get a little tricky. We seen lots of water heaters installed theoretically outside the living space, such as in an attic, crawl space, or garage. In most houses, though, these areas are, in fact, connected to the house, and combustion gasses that leak can get into the house.

If the water heater is in a space with a leaky return duct, the heating or cooling system can literally suck the flue gasses out of the water heater and spread them throughout the house, even if everything is installed to code. By getting a sealed combustion water heater, this problem can be eliminated.

To sum up: 1) think about how much hot water you need; 2) think about how much you're willing to pay to avoid occasional inconvenience; 3) get real estimates for installing different types of high efficiency units; and 4) compare prices in your area. Electricity and natural gas prices are relatively stable. Bottled gas prices fluctuate a lot, and depend on how much gas you use. If you're only using gas for water heating, you'll pay a lot more per gallon than if you're using it for heating also. Be sure to call several suppliers, tell them what you'll be using the gas for, and ask about installation charges, too.

The yellow "Energy Guide" label will give you a sense of the efficiency of various units. Look for units whose estimated annual energy use is near the bottom of the range listed for that type of unit. If your water heater is more than 10 years old you should be thinking about a replacement. It may last another 10 years, but chances are it will die well before that. If you wait until it dies, you'll have to make all the decisions in a big hurry, which is not conducive to getting the best value.