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Subject:
Re: OT-tankless water heaters
Response To:
OT-tankless water heaters ()

Barry Irby
My knowledge on these things is somewhat dated. The other posters have raised some good points.

Start with: Heat gets out of a tanked water heater three ways: You use it, Stand by losses, and up the flue (gas).

Several things to consider. Small to medium tankless heaters may not provide enough hot water for more than one thing at a time. They have a flow rate and burner capacity that determines how many Gallons per minute they can deliver. OTOH, larger units require a huge gas input to generate lots of hot water and may require a fairly high flow rate to activate the burner. Turn on a small trickle and you get cold water.

I have seen houses that have 150,000 btu burners in the water heater and 80,000 in the furnace. This could require upgrading your entire gas system if you have it, all the way from the street.

The length of time it takes to get the hot water to a location is a function of the distance from the source to the use, not so much tank or tankless.

Time is also affected by pipe diameter, 3/4" pipe takes longer than 1/2".

Exterior mounted tankless heaters must have freeze protection.

You can cut standby losses by insulating the tank and pipes. All newer heaters come with a flow restricter that prevents water circulating into the pipes and cooling off due to thermosyphoning.

I looked into putting a little pump under my kitchen sink to circulate the hot water up to the sink without flushing it down the drain. Kits are available. I was going to use a timer. Push a button and it would run long enough to bring you hot water and shut off.

Electric versions require huge power supplies, sixty amps or more.

Another thing to consider is that your new heater will most likely be physically larger that then old one. New standards require more insulation, a good thing, cutting standby losses, but may not fit the old space.

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