Tankless water heater and pipe size

UDRider

UDRider

FLCL?
So I am thinking of getting tankless water heater.
I got two quotes. One plumber says I can get away with 1/2 line, another says I need 3/4.
I was thinking of going with 160k max BTU Rinnai.
Max distance from has meter is 40ft. Although looks like what's going in is 3/4 already, so somewhere under the house it splits to 1/2 to feed the water heater. So 1/2 length is probably even less.
Looking at Rinnai website seems like 1/2 should be enough: https://www.rinnai.us/faq/tankless-...e-does-a-rinnai-tankless-water-heater-require

Going to get a fourth quote (third one didn't even both to came out so off the list), but does BARF collective say?
 
nakedape

nakedape

Well-known member
My buddy has one and since it's external I can see it's 1/2" Works fine.

You might want to check the mineral levels averaged over a month or three, or historical data, so that the element doesn't cake up and fail. He's on #3. We have 700-900ppm calcium carbonate year round.
 
sprorchid

sprorchid

Well-known member
I had a Takagi put in when I bought my house.

Mine is inside, if it will help you I can text you pics for the pipe size, et al. I'm not as handy as you, paid folks to install mine.
 
UDRider

UDRider

FLCL?
nakedape said:
My buddy has one and since it's external I can see it's 1/2" Works fine.

You might want to check the mineral levels averaged over a month or three, or historical data, so that the element doesn't cake up and fail. He's on #3. We have 700-900ppm calcium carbonate year round.
Click to expand...

I have water softener. :thumbup

sprorchid said:
I had a Takagi put in when I bought my house.

Mine is inside, if it will help you I can text you pics for the pipe size, et al. I'm not as handy as you, paid folks to install mine.
Click to expand...

Not sure I am handy enough to tell from pic, but thank you for the offer. :thumbup


Crawled under the house. Looks like 3/4 line goes almost all the way, and then splits to 1/2 to the current heater for like 5 ft or so.
 
B

BURNROPE

Well-known member
A conventional water heater is a good emergency supply of water after a natural disaster such as an earthquake.
 
Climber

Climber

Well-known member
UDRider said:
Yes that is exactly what is happening. From meter 3/4 then splits of to 1/2 for like 6 feet to the current heater.
Click to expand...
The heater should be getting fed by 3/4 unless it is only going to 1 fixture, in which case 1/2 inch is fine.

If the water heater is feeding multiple fixtures, then it needs 3/4 in and 3/4 out and 3/4 pipe to the final split. Otherwise you will have flow issues if two fixtures require hot water at the same time.
 
UDRider

UDRider

FLCL?
Climber said:
The heater should be getting fed by 3/4 unless it is only going to 1 fixture, in which case 1/2 inch is fine.

If the water heater is feeding multiple fixtures, then it needs 3/4 in and 3/4 out and 3/4 pipe to the final split. Otherwise you will have flow issues if two fixtures require hot water at the same time.
Click to expand...

What do you mean two fixtures? There are two bathrooms with showers. Is that what you mean?
 
Climber

Climber

Well-known member
UDRider said:
What do you mean two fixtures? There are two bathrooms with showers. Is that what you mean?
Click to expand...
Yes. End points for the water.

You actually have at least 5 end points, 2 showers, 2 sinks and 1 kitchen sink.

This means that you should have a 3/4 in pipe coming out of it, a 3/4 inch pipe going to each bathroom, changing to 1/2 inch when you hit the split to bath and sink. Kitchen can have 1/2 inch pipe once it splits off. If you have washer/dryer, that would be an additional end point (fixture) which would follow the same rule as kitchen.

Have you ever gotten a sudden jolt of hotter water in the shower when somebody flushes the toilet? That is due to 1/2 inch pipe feeding both. With a 3/4 inch pipe feeding both, there is still a drop in flow but the effect is much smaller. This is for the cold line.
 
UDRider

UDRider

FLCL?
Climber said:
Yes. End points for the water.

You actually have at least 5 end points, 2 showers, 2 sinks and 1 kitchen sink.

This means that you should have a 3/4 in pipe coming out of it, a 3/4 inch pipe going to each bathroom, changing to 1/2 inch when you hit the split to bath and sink. Kitchen can have 1/2 inch pipe once it splits off. If you have washer/dryer, that would be an additional end point (fixture) which would follow the same rule as kitchen.

Have you ever gotten a sudden jolt of hotter water in the shower when somebody flushes the toilet? That is due to 1/2 inch pipe feeding both. With a 3/4 inch pipe feeding both, there is still a drop in flow but the effect is much smaller. This is for the cold line.
Click to expand...

Umm I think there was Miss communication my bad. I was referring to gas line that feeds the water heater. The water pipe situation is a whole different can if warms, that I am not touching yet. :laughing
 
Climber

Climber

Well-known member
Ah. Yeah, 2 different things. :laughing

Back when I did plumbing to put myself through school, we never went below 3/4 inch black pipe for gas piping, but the furnaces were also very close to the water heaters and that was New England.
 
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