Tankless Water Heater

Rick Kelly_2

I have a 1700 sq ft two story house and a 50 gal water heater and am considering switching over to a tankless water heater. Currently, I have installed a pump underneath the sink at the furthest location from the water heater in order to provide "instant" very warm water at every faucet in the house. It does this by providing a small "constant" flow of warm water throughout the house.

If I install a tankless water heater, will I need to remove the pump mentioned above? Or will it not have any affect on the tankless water heater? I'm thinking that because of the constant flow that the pump creates, the tankless water heater will run constantly.

Alan(CaliforniaRadiant)Forbes

Tankless

It may depend which tankless water heater you buy. Let's say you install one of the models made by Takagi which I am most familiar with. You can still use your recirc. pump, but it has to move at least ¾ gallons per minute before the Takagi will turn on.

No, the Takagi will not run constantly since I believe it has temperature sensors at the inlet piping. So if hot water is returning to the Takagi, it will modulate the burner down or turn it completely off.

I believe the Rinnai and Noritz heaters will do the same. Check with the manufacturer.

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Rick Kelly_2

Tankless reply

Thanks for your quick reply, Alan. In your opinion, is Takagi the best brand available? Who sells it? Can you recommend a reputable installer in the Pasadena, Ca area?

Jack_23

Rinnai

Recirc on the Rinnai is a function of flow and gpm. The min firing rate is 15kbtu. The unit can fire only if it can USE the 15k. therefore on a recirc at 1gpm you would have a 30F delta T before the unit would fire. At 2gpm it is 16F and at 3gpm 6F. You can read the flow rate on the touch pad (a really neat eature). I really do not like recirc. on a 3gpm flow rate on a poorly controlled recirc that runs constantly (and some do) you are putting 1,500,000gal/yr thru the unit. Seems excessive.

TW

Recirc Pump on Tankless Water Heater

"Clarification"
The recirc pump on Rick's system is a Laing Autocirc pump that only cycles to operate when the self timer is set to operate, which is typically when the residents (2 working adults) are home and when the temperature at the homes highest use point(kitchen sink) and point furthest from the waterheater, is below 85 degrees. In Rick's case the timer is set to operate a couple of hours in the morning and 5 hours in the evening. In Rick's case the pump operates approximately a 1/2 hour or so total, per day. The temperature controlled pump is inactive when water is being utilized at the sink. This is 2 pipe system, there is no 3rd pipe return. The cooled off hot water is returned to the hot water tank via the under sink cold water line and the heater's supply line. The pumps water flow rate on Rick's plumbing size and length is very low, 40ft in 3-4 minutes. Rick's 1960's construction era home's pipes have little or no pipe insulation but have little or no exposure to outside walls or cool crawl space air as in an attic etc. The heating degree days in Southern Calif where Rick lives is so low the pump rarely operates and was installed principally for water conservation and instant hot water convenience. The kitchen sink is is between 40 and 50 feet from the water heater, 3/4 inch copper.

I've been a "wethead" fan of Dan Holohan's for almost 20 years and hope to do a radiant floor project soon. Are there any west coast trade classes?