Main Gas line BTU Capacity

Old 05-17-17, 03:02 PM
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Main Gas line BTU Capacity

Good afternoon everyone, the area in which I live the government is offering a rebate for homeowners to replace their 'inefficient' Conventional (Standing Pilot) hot water tanks with 'energy efficient' tankless systems. So I am contemplating this because the rebate is about $1000 as well a local supplier is offering to match that rebate if the work is done by them. Also given that our hot water tank is only 40 gallons and 16 years old is another reason.

However I am concerned that our main gas line from the meter might be under capacity given that tankless systems require anywhere from 17K~200K BTUs. I have done some rough calculations and with my limited knowledge seem to have determined that we may be limited to around 240K BTUs.

I believe that the gas line from the street going into the meter is 1.5 inches but is immediately sized down to 1 inch, then runs through the meter and the meter outputs a 1 inch line 40 feet to our first appliance (a 81,000 BTU input/61500 btu output furnace) I think it is scaled down to 3/4 inch at this point, then another 3 feet of 3/4 inch to the next identical furnace, and then a scale down to 1/2 inch for the 36K BTU hot water heater.

The tankless system that is being suggested does state is fine to work on a 1/2 inch line but given what has been listed for the BTUs of the 2 furnaces would we be running into a problem if all 3 appliances kicked on at the same time?

I should also make note that we are also looking to add a gas line for a BBQ as well. I think the total BTU on that guy would be around 69K BTU.

So with the calculation of 240K BTU on our main line does that mean that so long as we dont have an appliance that requires more than 240K BTU we are ok or does it mean that we are only allowed up to a combined sum of that main line BTU, so 81K+81K+36K=198K means we are under 240K BTU, where as 81K+81K+200K+69K=431K = BAD?

Thanks for any input and advise
Old 05-17-17, 03:51 PM
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Here in the states it goes by the distance or farthust appliance from meter and size of pipe off meter into the home.

If your farthest appliance is 50 ft and the line is 1" into the home then that supports 284K btu..

You would not be able to add the tankless to the existing line..

What you would need to do is tap off the meter and run a dedicated line from meter to tankless.

This line would probably need to be 1" because most tankless heaters that work well are at least 200K btu..

Its my opinion tankless heaters have thier place but more often then not they are a waste of $$$. It will probably cost you more down the road long term with maintenance and repair/replacement costs..

They dont save all that much. Couple that with hot/cold slugs of inconsistent temps, it will make you wonder " What was I thinking?"

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