Add a tank to a tankless hot water heater?

It may not seem sensible at first but adding a small tank to a tankless hot water heater can be a smart thing to do. Why? There are two key problems that can arise with tankless, or on-demand, hot water heaters. They are a cold water surprise when two showers are taken a few minutes apart, and a loss of pressure when two or more people are using hot water.

Basically, the problem occurs with after one person has showered the water in the pipes should still be hot for a while, assuming they're well insulated. But since the heater itself is not the water there will cool quickly. Once a second person starts to shower that cold water is moving down the pipes before the heater has kicked in resulting in a sandwich of cold water in the pipes that will hit the shower shortly.  By adding a ten-gallon heated tank to the system, the cold water surprise can be totally eliminated. The cold sandwich is tempered in the tank before it moves on up the pipes.

The loss of pressure is another problem that requires the addition of a small pump to resolve. For the whole story see Michael Chandler's article in Fine Home Builder magazine.

Comments

[Water heaters]

The only solution is to turn off some of your water jets.The 9.4 gpm tankless and the problem is, is that I am installing a custom shower with 6 body jets and shower head which equals 17.5 gpm..How would I get that out of my tankless?

[Fred]

Dave,
The only solution is to turn off some of your water jets. Frankly, 17.5 gpm for a shower is a shameful waste of water, which is fast becoming a precious resource. This seems a lot like revving up a hummer for your daily commute to work.

[dave]

I dont know for sure if this will solve my problem. I installed a 9.4 gpm tankless and the problem is, is that I am installing a custom shower with 6 body jets and shower head which equals 17.5 gpm. How would I get that out of my tankless?

[Kroeze]

What appears to be the best green? A tankless set-up. Certainly the electric models use a lot of watts around 9,000 for brief periods of time and then minimum when not in operation. Thermal however is more expensive up-front but pays for itself in about 6-8 years it appears.