tankless gas water heater question

bob eck

Most tankless gas water heaters require 140,000 up to 199,000 BTU on residential models. In a lot of homes the gas line is 3/4". I believe on most jobs when totaling up all BTU needed to run all gas appliances the 3/4" line will not be big enough so if the home owner wants to have a tankless gas water heater installed they need to up grade the gas line and that is a major expense when trying to sell TGWH. Does any tankless gas water heater manufacturer have the capability of making the TGWH have priority over the gas furnace or gas boiler. When the TGWH turns on the power from the thermostat to the gas furnace or boiler would be turned off this way the original gas line in the house would be big enough to supply the TGWH and you the contractor would not have to up grade the gas line to a larger size

lchmb

I would

resize the line adding in for possible additions down the road and be done with it. I dont know of a manufacturer who would offer this but think your just asking for trouble if something goes wrong, or someone over rides it....

Zman

Can You Increase Pressure?

I am assuming you have a 1/4lb system. How about going to 1/2lb and  adding a regulator at each appliance.

HDE

Tankless companies don't

But it wouldn't be hard to apply a gas pressure switch from Honeywell to do that.

However, it would be better to apply a quality flow switch to the cold water line inlet of the tankless, that way the heating equipment input contact can be broken before the tankless ignition sequence completes.

bill_105

How about electrically?

Couldn't  you have the flow switch by itself actuate the TT terminals of a Taco sr501. Then, after removing the jumper. complete the circuit  of the tankless from the first relay. The use the second relay too break the circuit to the boiler.

bill_105

I just heard it

There is a hotel in Dawson City YK that used a wastewater heat retreival system with a tankless. When the tankless turned on it turned on a three way valve to direct water to a heat exchanger. So why not shut off a boiler? The water up there comes out of the  ground pleny cold. Actually I don't know how he did exactly. Quite inventive