By combining a small buffer tank with the tankless hot water heater some of the annoying problems that plague tankless water heaters can be solved and at the same time the standby losses can be reduced by maybe 80 percent or so.
Hybrid water heaters are beginning to attract some attention. The new tankless / storage type hybrid hot water heater combines a tankless water heater with a tank… what a novel idea. The tank though would not be comparable in size to a traditional storage water heaters tank. It can be substantially smaller since it isn’t trying to be the source of all the hot water, it’s just to aid in some of the problems traditional tankless water heaters have.
With a buffer tank the unit can deliver hot water faster since it doesn’t have to heat the water first, there is sufficient hot water in the tank to begin sending water to the fixtures right away just as a storage water heater would do. Before the buffer tank runs out of hot water the tankless heater gets up to temperature and begins supplying the hot water.
Another problem solved by the buffer tank is the inability to get a trickle or a low flow of hot water from the fixture. Typically the flow would not be enough to turn on the tankless water heater. With the buffer tank that problem is solved. The tankless burner part of the water heater doesn’t turn on until it detects need for additional hot water beyond what the buffer tank can supply.
Hot water circulating systems normally are incompatible with tankless water heaters, but with the addition of the tank that too is resolved. Hot water circulating systems will work with the hybrid water heaters.
You will still need a larger than standard gas line and larger venting than storage water heaters require; there is still that big burner to supply with gas.
The Eternal Hybrid Water Heater has an interesting design that is substantially different than other hybrid water heaters. The new design takes the flue exhaust from the tankless portion of the heater and runs it back through a heat exchanger built into the buffer tank, increasing the efficiency of the heater.
It uses 44 baffled stainless steel pipes for maximum heat transfer. The flue gases emerge from the heater cool enough to vent with PVC pipe. The tank is only half the size of a typical water heater but puts out about %300 as much hot water. It’s also ultra low in NOx emissions and other greenhouse gases. The Eternal hybrid water heater is a green plumbing product by any measure.
On top of that, the stainless steel tank has a 20 year no-leak warranty!
The Eternal Hybrid Water Heater Models GU-20 and GU-26 qualify for a Federal Income Tax Credit when installed between February 17, 2009 and December 31, 2010. Other Rebates and Grants may be available under the Appliance Stimulus Program, the Weatherization Assistance Program and state and utility rebate programs.