"Does a water heater timer make sense?"
Column #819 10/30/2010
On The Level
Q. We are gone from the house during most of the day and we are looking to minimize our electrical use all around. We have a programmable thermostat for heat and air. We’re thinking a timer for the hot water heater might help. What are the pros and cons of a stimer?
A. Certainly more pros than cons. Basically the timer is a switch that you control to turn itself on or off at whatever time of day you desire. People do that with lights in the house when they go off on a trip so the house looks occupied.
Traditional electric water heaters are little more than big metal tanks that have heating elements in them that are controlled by integral thermostats factory set at 120ºF. They are adjustable and can be set higher or lower but the 120ºF setting is an anti-scalding setting for basic user safety.
Where traditional tank water heater inefficiency enters in-- compared to on-demand or “tankless” water heaters-- is the energy they lose in their stand-by mode-- and you’ve figured that out. They are designed to hold water at the set temperature round the clock waiting for someone to use some. If you think about it, most folks really don’t use that much hot water over a day’s time and when they bathe they actually mix water coming from the hot tap with cold to bring it down to a more comfortable temperature-- about 100ºF. Modern showers use water at 2.5 gallons per minute. Doing the math for an average shower length might yield a use rate of less than half of the water heater’s capacity. You are rightly concerned about that tank staying hot all day and all night waiting for about fifteen minutes use. It’s a big thermos bottle slowly sucking electricity to keep hot.
When I am totally on my own in the house I’ll flip the breaker to the water heater off and keep using hot water at my regular rate waiting to sense the difference. It’s a 50 gallon tank, like most. It takes a couple of days before I’m forced to turn it back on. You can save an additional 5%–12% of energy by installing a timer that turns the water heater off at night when you don't use hot water and/or during the utility's peak demand times. If you’re handy you can install the timer yourself. If not, call an electrician. They cost in the $60. range but they can pay for themselves in about a year. You can contact BGE to see what they are offering in the way of “smart meters” etc to get a better handle on your usage.
Some homeowners wrap their water heaters with an insulation blanket but I have never seen a payback period analysis that I trust on them but it certainly can’t hurt. Any penetration of the water heater’s own insulation envelope leaks heat and heat is energy and it costs. Those penetrations include where the heating elements enter the tank, where the inlet and outflow pipes and the temperature pressure relief valve are piped and the drain-cock at the bottom.
Another item now in use with newer water heaters is a thing called a heat trap and they are installed at both inlet and outflow pipes. They prevent heat from convecting up those pipes as the heater sits waiting for use. They can save you around $15–$30 annually on your water heating bill. Heat traps—valves or loops of pipe—allow water to flow into the water heater tank but prevent unwanted hot-water flow out of the tank. The valves have balls inside that either float or sink into a seat, which stops convection. These specially designed valves come in pairs. The valves are designed differently for use in either the hot or cold water line. A pair of heat traps costs only around $30. However, unless you can solder a pipe joint, heat traps require professional installation by a plumber. Heat traps are most cost effective if they're installed at the same time as the water heater.
After you’ve done all you can to conserve what heat is in the water heater I’ll address the temperature setting. I know water heaters show up preset at 120ºF but there are a lot of microbials that can thrive in that level of hot water. Legionella, the bug that causes Legionnaire's Disease, can survive in water up to 131.9ºF and so can a bacteria called SRB, or sulfur reducing bacteria. That’s the one that gives us that rotten egg smell, especially on well water. If you are concerned about either and don’t have small children around then turn it up to 140º. It’ll heat up to that level and cool somewhat while the timer has it off but a cycle of that degree of heating should keep the inside of the tank sanitary.
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