Tankless conversion, from two 40's to one tankless

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Tex plumb

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I have two tank heater 40 gallon. Each one has a dedicated line from the meter(1/2”). If I connect both of those 1/2” lines at the end of the run to make it a 3/4” line. Will that be sufficient but to remove tank heater and install a tankless?
 

Tuttles Revenge

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Yes, you can combine the Two 1/2" lines to a larger diameter pipe to equal its flow rate.

Pipe Size (Sch. 40)I.D. (range)GPM (w/ min. PSI loss & noise)
1/2"0.5 - 0.6"14
3/4"0.75 - 0.85"23
1"1 - 1.03"37
 

John Gayewski

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To keep things equal you'll need to up it to 1" which is actually oversized. Equal likley won't matter and 3/4" will likley be enough. Depending on supply pressure and how much hot water demand you actually need. Generally 3/4" for the hot on a house should be good.
 

Jeff H Young

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I thought he was talking gas . Can't be water three lines coming from the meter 2 dedicated half inch lines plus the main ? assuming meter is at the street
 

Terry

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I thought he was talking gas . Can't be water three lines coming from the meter 2 dedicated half inch lines plus the main ? assuming meter is at the street
I thought he was talking about gas lines to his 40 gallon gas tank water heaters too.
Is the question about supplying gas to a tankless? Or is it water you're sizing?
 

Tuttles Revenge

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OOH... Yeah.. I guess I assumed it was water lines.. But more likely gas.

The most BTU of a tankless water heater is 199kBtu so you need to have that amount. I've never combined gas lines and if they're coming from 2 meters... that sounds like a No Go situation right there.
 

Jeff H Young

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Assuming gas I suppose you could combine 2 1/2 inch lines to provide roughly 200k btu if the run to meter is short like 20 ft .
just a ballpark estimate and combining the gaslines not very conventional and if pulling permit might be issue . but existing work I think you might just make it .
 

Tuttles Revenge

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The Navien draws in gas rather than being supplied with gas. But it also needs to be the first fitting after the meter in order for it not to starve other fixtures of their gas.
 

Tex plumb

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Yes I am talking gas. Two 1/2” wardflex gas supply. From the gas meter the run is around 50-60’ across the attic. I am thinking of just installing a 1” wardflex across to be sure. Then at the heater drop to 3/4”.
 

Jeff H Young

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Yes I am talking gas. Two 1/2” wardflex gas supply. From the gas meter the run is around 50-60’ across the attic. I am thinking of just installing a 1” wardflex across to be sure. Then at the heater drop to 3/4”.
I see nothing wrong with 2 lines you just have to verify btu or cubic ft hr if its undersize then youll have to run new line
 
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