[mrtuba9]

Hi All,

New to these forums and I have a quick question. I want to install a tankless water heater and see that they require a 3/4" water supply. We have a 1 1/2 bath ranch and right at the meter, the 3/4" line is stepped down to 1/2. That line runs 40 feet or so before it enters the old tank water heater. Can I just add a 1/2 to 3/4 adapter and run a 3/4 line to the tankless?

Thanks for any help.

Bob

 

[AllanJ]

I would say no problem doing it as you described.

Most likely the heating capability (BTU rating) of your tankless heater is not sufficient to gain any advantage from the increased flow (in gallons per minute) possible using 3/4 inch pipe. When you increase the flow rate too much for the heater then the temperature of the water coming out drops.

 

[Plumber101]

When you have problems make sure you have Allen's number.

Water service needs to be up graded to 3/4", flow and pressure are to different things

As a Rinnai installer if there isn't 3/4" plumbed from the water main to the tankless unit I walk unless HO is willing to upgrade.

 

[kenmac]

When you have problems make sure you have Allen's number.

Water service needs to be up graded to 3/4", flow and pressure are to different things

As a Rinnai installer if there isn't 3/4" plumbed from the water main to the tankless unit I walk unless HO is willing to upgrade.

You are 100% on this one:yes:... Large water lines & large gas lines(depending on BTU'S) Most I install are 199,000 BTU'S

 

[mrtuba9]

When you have problems make sure you have Allen's number.

Water service needs to be up graded to 3/4", flow and pressure are to different things

As a Rinnai installer if there isn't 3/4" plumbed from the water main to the tankless unit I walk unless HO is willing to upgrade.

Hi Plumber101,

Would you mind another question? As I mentioned, the main line off the meter is stepped down from 3/4 to 1/2. Could a Tee be made from the meter, with 3/4 going to the tankless, and the 1/2 feeding the cold as it does now?

Thanks,

Bob D.

 

[darsunt]

You can install a tankless anywhere, right? It is so small. So I would run a 3/4" line off the water meter, place the tankless unit close enough so I could run 3/4" line direct off the 3/4" line to the heater, THEN run the 1/2" inch lines from the 3/4" line for the rest of the house. If this is possible.

If a tankless unit is rated at 3/4" that means 3/4" from meter to tankless heater. I would avoid making a tee at the meter, and I would follow manufacturers specs exactly. Of course it MIGHT be possible to do shortcuts on this installation (such as running an adapter off a 1/2" line) but I wouldn't try them unless I was absolutely certain of the possible consequences.

 

[Clutchcargo]

I would place the heater as close to the point of use as possible. That way you don't waste water waiting for it to get warm.
0.02

 

[Scuba_Dave]

Hi Plumber101,

Would you mind another question? As I mentioned, the main line off the meter is stepped down from 3/4 to 1/2. Could a Tee be made from the meter, with 3/4 going to the tankless, and the 1/2 feeding the cold as it does now?

Thanks,

Bob D.

Yes, keep 3/4" to the tankless
A plumber can branch off to supply water to rest of the house
Myself I had my plumber run 3/4" to the main junction where water then branched off to several 1/2" lines

I'd also keep the tankless as close to point of use
That's easier to do with electric
Not always possible with gas

 

[Plumber101]

Yes, keep 3/4" to the tankless
A plumber can branch off to supply water to rest of the house
Myself I had my plumber run 3/4" to the main junction where water then branched off to several 1/2" lines

I'd also keep the tankless as close to point of use
That's easier to do with electric
Not always possible with gas

Yes, as long as the tankless is being fed with 3/4"