19 July, 2012

Instantaneous (Tankless) Water Heaters

You know, I’m getting downright cheap in my old age.  I just hate to spend money for utilities if I’m not home to ‘enjoy’ them.  One example is that I lower the furnace thermostat when I go to bed or when I’m away from the house.  My household critters don’t seem to mind as they have fur coats and they make use of each other to keep warm (and sometimes my sofa, too).  I use compact fluorescent and LED bulbs for lighting and I even have solar powered spotlights to illuminate the back porch.  I’ll try anything to save a buck.

But there doesn’t seem to be much we can do with tank-type water heaters.  I’ve added tank blankets and pipe insulation, but it doesn’t seem to save all that much.  Since 2004, storage tank-type water heaters have been mandated (by the U.S. Department of Energy) to be more energy efficient as well as a combustible vapor requirement.  Despite that (according to the DOE), water heating accounts for 20% or more of an average household's annual energy costs. So, the operating costs for gas storage tank water heaters average more than $200 annually.

Rinnai whole house water heater
A tank-type water heater maintains the water temperature to the thermostat setting on the tank.  The heater does this even if no hot water is drawn from the tank.  This is due to "standby loss": the heat radiates from the walls of the tank and out the flue pipe. These standby losses represent up to 20% of a household's annual water heating costs.  One way to reduce this expenditure is to use a tankless (also called " demand " or "instantaneous") water heater.

Instantaneous water heaters are common in Europe and around the world.  When I have visited my relatives in England, I noticed the water heater in their homes were mounted on the wall in the kitchen.  Unlike the common tank water heaters, tankless units heat water as it is used, or “on demand”. A tankless heater has a sensing device that is activated only when you open the spigot, the heater will fire up and give a constant supply of hot water.  Junior can do his normal 40-minute shower and there’s no waiting for hot water for your shower when he is done.

Ariston demand water heater
The largest gas units, which may provide all the hot water needs of a household, are installed centrally in the basement or small units at the point of use, depending on the amount of hot water required. For example, you can use a small electric unit as a booster for a far-off bathroom, dishwasher, or laundry. These units are usually installed underneath a sink or nearby in a closet.

What I have learned from using centrally-located tankless heaters is that you need to find the highest flow rate you can get. Also you may need modify your water-use behavior a little bit.  Despite manufacturers’ claims, you still do not get the same flow rate of water as you would with a tank type heater.  With a 3.5-gallon per minute showerhead running and a large water-using appliance cycles on, one or both may not get much hot water.  So hopefully, you get to finish your shower before Junior decides to turn on the dishwasher. 

Now if I can only figure out a way to convert the excess energy that my dogs have to heating the house.