Water Heaters: At Your Beck and Call

by Mike Forbes, from the February 2001 Newsletter

It's been several months since I've written for this newsletter. In the meantime, the new year has come and it appears as though we're on the brink of a nationwide energy crisis. Get ready for our cheap power/fuel to disappear.

Hopefully, this will force folks to re-evaluate their energy use and turn towards more appropriate technologies. I use the word appropriate instead of alternative because I think it conveys a different idea. Nuclear power is an alternative power source for us here in Idaho but I don't find it appropriate. I think wind power is much more appropriate for us, you, and the ecosystem.

This explanation is a little diversion, however. In this article, I'm going to look at the hot water tank. It's a concept that bewilders me.

The majority of us have either an electric or gas water heater in our homes that heats up between 40-52 gallons of water to a set temperature (usually 120-140 degrees F). When hot water is used, cold water replaces it in the tank where fuel is used to heat it back up to the set temperature (for the sake of this article, we'll call both electricity and gas fuel). Fuel is also used to heat that same water back up when it cools sitting in a tank "waiting" to be used. It does this 24/7 whether we are using water or not.

The hot water heater is typically the most common consumptive appliance in the home—with the exception of electric baseboard heaters. An ordinary 40-52 gallon tank uses between 3500-5000 kwh (kilowatt hour) of electricity per year. Most large "efficient" refrigerators use about 900 kwh.

The problem with hot water tanks is that they keep the water hot at all times even when you are not using it. The insulation on the tank helps keep the water warm but doesn't do it sufficiently. Also as the hot water in your pipes travels to the faucet, it cools in the wall. That means the heater has to generate excess hot water.

Think about how much time you spend with a hot water tap on per day and I'll bet it is nowhere near 24 hours, maybe 1 hour if you take numerous showers. Why keep the water warm when you aren't using it?

Europeans and Asians figured out years ago how to deal with this problem. They use on-demand water heaters.

An on-demand water heater works like this: when you turn the tap on, the heater detects water flowing and activates a burner that heats the water to a set temp (120-140 deg F). When the tap is shut off, the burner turns off. There is no tank to store water in. Plus, you never run out of hot water. This sounds too good to be true, but it is really this good.

There are a couple of issues you need to be aware of. The heater can only heat the water to its set temperature for a given flow rate. In other words, if your heater is rated for a 70 degree F rise at 3 gallons per minute (gpm), then you can flow 3 gpm out of your faucet at 120 degrees F—if your incoming water is 50 F (most water is about 50-55 F).

Problems surface if you open 3 faucets at the same time, and try to flow 6 gpm all at once. The burner won't be able to provide you with all the hot water that you request. It takes a little communication between family members to have an on-demand system function properly.

There are many sizes of on-demand heaters. I've only researched ones sized for a residential home. They range in price from about $500 to $1000 and can run from either propane or natural gas. If reducing your electric bill is your goal, don't even bother with electric on-demand heaters, they can use upwards of 28,000 watts of power when running. The companies that have a good reputation are Aquastar (Bosch), Paloma, and Takagi. All good on-demand heaters are built in Europe or Japan and are imported.

I'm just about ready to place my order for an on-demand heater. Until now I've made my electric water heater much more efficient by turning the thermostat down to 120 F. I didn't rely on the gauge on the heater, I actually measured the water temperature at the tap after letting the heater sit for 24 hrs. It was surprising to see that the gauge was not accurate. After reducing the water temperature, I added extra insulation to the heater. I started with one of the Reflectix® water heater blankets (about $15) then I built an enclosure about 14-18" from the water heater and filled it with bags of cellulose and rigid insulation. I estimate that my water heater is enclosed by about R-100 of insulation. I have noticed a significant reduction in energy usage after doing this. This is a temporary fix until I install an on-demand heater later this month.

Here's one last hot water conservation message. When washing their hands, many people instinctively turn on the hot water tap and wash their hands in cold water, without waiting for the water to get hot. Doing this moves hot water from the insulated tank to the house pipes where it cools, causing the hot water tank to run unnecessarily.

Mike Forbes is an expectant father who lives with his sweetie in an old drafty farmhouse soon to be efficient, off-grid farmhouse. He is available for further commentary or information, by email at mikeforbes@moscow.com.

 

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