tankless gas water heater & grundfos comfort pump recirc system

bob eck

Hi

Has anyone installed a tankless gas water heater (NORITZ, RINNAI OT TAKAGI) with a GRUNDFOS Comfort Pump System model UP15-10SU7P/TLC (grundfos pump with comfort valve no return line needed to be run back to the water heater.)?

I know if you use a recirculation pump on a NORITZ tankless gas water heater the heat exchanger warranty goes from 10 years down to 3 years.

I was told to come out of the tankless gas water heater and go into a 2 to 6 gallon electric water heater and then use a recirculation pump from there so you would not be recirculating through the tankless gas water heater and reducing the warranty on the heat exchanger.

I just wanted to know if anyone has installed a system this way and if it worked for them?

Thanks for the info.

Thanks Bob Eck

Erin Deibert

Recirc to continuous water heater

The problem with recirc through these heaters is as the return water increases the flow through the heater needs to increase to take the Btu out of the heat exchanger. Most of these heaters have a minimum firing rate of about 45,000Btu/h. If your flow can not accept that many Btu's than the high intensity burner will start oxidizing away the wall of the that exchanger thus shortening it life. The problem is most units start firing at .5gpm. As a heating designer I get asked about tying heating circuits to these units and I have seen what long exposure to small loads can do to these heat exchangers. The best solution is to add a storage tank and recirc to the tank.