Q Your recent column on saving energy with a water heater missed the boat. You never mentioned on-demand water heaters. We have the Rinnai on-demand water heater from Japan and use it for our three bathrooms. We never feel that we're out of hot water but are saving money. It's not operating when we're not using it. In addition, we don't have to worry about turning if off when we go on vacation.
A If it works for you, that's good. On-demand or tankless water heaters can save energy. But they don't always work as well as you describe.
Tankless water heaters have some inherent issues that can make them less desirable than traditional tank water heaters, at least in Minnesota homes, said Phil Smith, energy specialist at the Minnesota Office of Energy Security:
• The internal supply of natural gas to the house may not be enough. Most homes are plumbed to have a supply of 300,000 BTUs per hour. A typical house has a mix of gas appliances: a furnace takes 60,000 to 100,000 BTUs to operate; a gas range 30,000 BTUs and the same for a gas clothes dryer. On-demand water heaters start at 140,000 BTUs, but commonly go up to 200,000 BTUs. In a busy household, with the furnace cycling while doing laundry and cooking, the internal gas pressure in the home can drop to the point that the appliances shut down.
• Having the right number of tankless units is critical for getting enough hot water. The number of bathrooms is part of the calculation, but how occupants use these bathrooms needs to be considered, too. A new home is more likely to be sized right for these devices than is an older home that needs to be retrofitted.
• Incoming water temperature, especially in winter, is an issue. On-demand heaters often depend on using incoming water that's 50 degrees or higher. But the water coming into many Twin Cities homes can be much colder than that, say, in the high 30s. We use water from lakes, rivers and above-ground storage towers, so our water is cold. A measurement in a St. Paul home showed that water coming into the home was at 40 degrees. (You can measure your incoming water temperature by running the cold water tap and holding a thermometer under the stream for five to 10 minutes to make sure you are measuring the temperature of water coming in from the street.)
Send your questions to Fixit in care of the Star Tribune, 425 Portland Av. S., Minneapolis, MN 55488, or call 612-673-7032, or e-mail fixit@startribune.com. Past columns are available at www.startribune.com/fixit. Sorry, Fixit cannot supply individual replies. Fixit appears every day except Friday.
