Radiator Supply Line

retired17

When replacing entire supply line hot from boiler to radiator and return from radiator to boiler, should the hot water go descending from 1 1\2 beginning of run to 3/4 end of run and ascending 3/4 to 1 1/2 for the return. The run is approximately 60 -75 feet

Thank you

Intplm.

Not necessarily, no. Are you referring to a hot water heating system or a steam heating system?

EdTheHeaterMan

YES. But not necessarily. It depends on the BTU per hour you are moving and if you are using a circulator or are just revamping a gravity system. This booklet Zoning Made Easy has all the info you need to answer your query

If we follow the Rule of Thumb guides outlined in the first few pages we will see that to have a noise free hydronic system, a 1/2" copper or steel pipe can move 1-1/2 gallon of water per minute (GPM). where that would be equal to 15,000 BTU per hour when the temperature difference between the inlet and outlet (supply and return) is 20°. So that is true for the rest of the pipe sizes in the shared pipe Rule of Thumb

Here we see that the larger the pipe diameter the more heat that can be transferred thru that pipe. If we also apply the 10,000 BTU per GPM rule, then we can select the proper pipe sizes when using a circulator to move the water quietly thru the system.

If You are connecting the 1-1/2" pipe to a boiler hat has a 100,000 BTU input with a 80,000 BTUh NET output then your pipe is way oversized for the task. Clearly you only need a 1" main pipe leaving the boiler room to handle 80,000 BTU of heater water. once you pass several radiators the will use up 40,000 of those BTUs, (4 GPM) you can then decrease the pipe size to 3/4" for the balance of the radiators on the system.

I hope this makes sense and helps you with your repiping.

retired17

https://forum.heatinghelp.com/discussion/comment/1849232#Comment_1849232

It is a gas fired water boiler

retired17

Thank you for taking the time to answer me. That was really helpful. Thanks again

retired17

so another question from the diy to the pro's. So I added all the feed and return from the boiler to the radiators in and out and back to the boiler. My figure is about 265 feet - 280 feet. So in this scenario with a 155,000 btu and about a 15.5 gpm, 9 radiators on second floor, 7 on first, should I reduce the feed from 1 1/2 out of the boiler to 3/4 to the last radiator and ascend the return from 3/4 to 1 1/2 back to the boiler?

Or should I just keep it at 1 1/2 to 1 1/4 the entire run

Thanks again

Gary

EdTheHeaterMan

That will depend on the size of the radiators.

It is easier to draw a diagram. but the math is pretty simple

Be Right Back with illustration.

pecmsg

how did you come up

With 156K BTU/h?

retired17

the boiler is 155,000 btu. The gpm is 15.5

retired17

Thanks ed, the radiators are all hydrotherm,

Total of 16

2 two footers

5 four footers

4 five footers

5 six footers.

EdTheHeaterMan

The two radiators at the end (White) only require 1.5 GPM flow so 1/2" pipe or copper will handle that

The total of the 4 radiators at the end (White and Purple) require 4 GPM shared pipe and 3/4" will be large enough for that.

The total of the last 7 radiators requires 8.2 GPM so the pipe size is 1" (Blue, Purple, and White)

Total for all the radiators except the first one on the line requires 14 GPM so 1-1/4" is required

When you add the first radiator to the system, 15.5 GPM is needed so you need to increase to 1-1/2" if you are using copper for the shared main pipe, or you can use 1-1/4" if you are using IPS pipes.

So to be clear, If you require 155,000 BTUh NET output (Not the boiler input) this is how your system might look. But you need to know the BTU output of the radiators and do your own math.

The diagram would look much different if you only have a boiler with a NET output of 100,000 BTUh or 80,000 BTUh

EdTheHeaterMan

I see you added Hydrotherm radiators in your last comment. are they Cast Iron Baseboard?

Also is the boiler BTU of 155,000 the input or the NET output? That makes a difference.

If you are repiping baseboards that were made by Hydrotherm, then you most likely have the copper tube radiators with the aluminum fin elements. I would not suggest piping that type of radiator as my diagram shows the cast iron radiators above. Series loop is more common with Copper/Alum Fin baseboard. At 155,000 total You will need at least 3 if not 4 separate 3/4" series loops.

Can you take a picture of the boiler ratings and the type of radiators you have.

retired17

sorry for not knowing all the information up front. The boiler is a Weil McLain cp7614262

Blr ult res 155h.

Baseboard.

The site said 155,000 output so if I add the 20% loss it’s like 124,000

I never done an entire system before, just replaced a few. Thanks for helping me out.

retired17

also the hydrotherm specs give a 600 btu per/ hr foot at 180 temp, gpm 4

retired17

https://forum.heatinghelp.com/discussion/comment/1849706#Comment_1849706

that is a great drawing, i totally get it

hot_rod

If you supply 180° to the system, and it drops a common 20°, the return or last heaters see 160°F

So use an average of 170° on the Hydrotherm spec sheet.

550 or even 500 btu/ft might be more realistic.

retired17

https://forum.heatinghelp.com/discussion/comment/1849725#Comment_1849725

great thanks will donthat

retired17

https://forum.heatinghelp.com/discussion/comment/1849717#Comment_1849717

https://forum.heatinghelp.com/discussion/comment/1849706#Comment_1849706

so would i also be able to use a copper manifold in places where the pipes for 4 of the radiators are close to each other from the feed or return?

mattmia2

You could use a manifold or make a manifold out of copper fittings, or you could even make a manifold out of black iron fittings. Sometimes it is easier to work with threaded fittings and nipples for something like that because you can rearrange it and change the direction of the takeoffs as you go.

retired17

https://forum.heatinghelp.com/discussion/comment/1849740#Comment_1849740

thanks matt