Many homeowners choose to install a condensing heater. A condensing heater is more efficient, but it does have two drains on it. The first drain is a pop-off valve in case of a over-pressure situation like a regular tank water heater and the second drain is for the condensing liquid. My heater came with a plug installed on the condensing drain. If you forget to remove this plug, or you don’t correctly install a drain to remove the condensing fluids your water heater will rust out of geyser price

The combustion byproducts of natural gas are water and other petroleum byproducts. The water that is produced from the combustion needs to be drained. I chose to drain the liquids into an outside area that is full of vegetation. You should consult your city and or county code on the proper disposal of the condensing liquid. Water heater manufactures provide mechanisms for treating the condensing liquid.

Recirculating Pump

Challenges with a tankless water heater is that they need a flow of water to turn the burner on. I honestly wasn’t sure that the recirculating pump that was installed on the existing tank heater in the house could generate enough flow to trigger the burner to ignite. Not wanting to take a chance with this installation, I chose to install a buffer tank that would keep a small amount of hot water always hot. Installing a buffer tank also eliminates the phenomena known as a “cold-water sandwich” when the heater takes time to respond to new demands on the hot water flow as faucets are turned on and off throughout the system.


I calculated that my house had over 6 gallons of water stored between the location of the water heater and the furthest faucet. You can calculate how much water is stored in your pipes with this formula:

Gallons = [1/2 * pi * [radius of pipe (in)]^2 * length (in)]/231

1 Gallon = 231 cubic inches

pi = 3.14159

Since I had to move 6 gallons of water from the furthest faucet to the heater, I felt that a 7 gallon water heater would be big enough for the demand. I purchased a 7 gallons point of use water heater from Bosch.


I connected the recirculating pump to draw water directly from the tank instead of the tankless water heater. The cold water from the point of use water heater is fed directly from the tankless water heater.

System Expectations

With this hot water system, you will never run out of hot water and you will gain the efficiency of a tankless heater. There is one design flaw with this system, and that is if you run the recirculating pump without drawing any hot water from any of the faucets the hot water coming out of the faucet will be luke warm. This is due to the fact that the water is constantly heating the pipes and slab if the pipes are in the slab. This heat exchange is a lot for the small point of use water heater to keep up with. In my house, I manually control when the recirculating pump is turned on and wait about 30 seconds for the hot water to reach the furthest faucet. I can then turn on the hot water and not notice any cooling of the water because the tankless water heater is mixing water into the recirculating loop.