use 1/2" or 3/4" for new branch lines?

heatingFun

I have a hot water heating only system. I am adding a room to it. The existing 2-pipe system has a 1" main line and 1/2" branch lines with BaseRay CI baseboards.



I have bought few WeilMcLain CI baseboards and want to add them into the existing system. The boiler and supply circulator are ready for this addition.



Both BaseRay and WeilMcLain CI baseboard have 3/4" connection openings.



My question is should I use 1/2" branch pipes as the existing branches' or use 3/4" branch pipes which the baseboards are designed for (I think)?



thanks,

Ironman

Depends

How many GPM do you need for the rad(s)? A 1/2in line will flow a max of 1.5GPM at a 20* Delta T= 15k btu's; a 3/4in line will flow about 4 GPM at a 20* Delta T= 40k btu's.

heatingFun

mix size of branch lines?

The HeatLoss Explorer 2 told me the GPM should be 2.9 in that new addition room. So that room needs 3/4" pipe branches. That means in the same zone, there are couple of 1/2" pipe branches and couple of 3/4" pipe branches. Is this ok? The 3/4" pipe branches will not be too hot?

CMadatMe

WOW

That's a huge load. My entire house only needs 3.6gpm. How big is this addition?

heatingFun

that is a wrong number

Sorry, that's for the entire zone, family room + living room.

The addition, family room, is 1.5 GPM.

icesailor

Branch Lines:

Back in the days before automobiles, I seem to remember that we (or I was taught) to use 1/2" pipe or tube to a emitter that was 15' or less. More than 15' was connected as 3/4". I think that you will find that if you measure the baseboard heaters that the 1/2" lines go to, they will be less than 15' in length. That the 3/4 lines go to longer radiators. We didn't know what it all meant, We just followed what the salesperson drew on a paper bag that came in the box full of fittings.

If it uses "Mono-Flow" or "One Pipe Fittings", it is a "One Pipe System". If not, it is either a Two Pipe direct return or a Two Pipe Reverse Return. Either way, use caution doing anything to the piping.

heatingFun

old house

My house was built in 1950s'.  They put baseboard all the way along the wall. My living room heat loss is 14030BTU/HR based on the HE2. But there are 21' + 19' + 9' = 49' CI baseboards. Two of them are longer than 15' and all them are 1/2" branch pipes. Similar in bedrooms, all baseboards are longer than 20' with 1/2" pipes.

icesailor

Rules of Thumbs:

I gave that as  Rules of Thumbs.

Those loops to the baseboards may or may not be properly sized.

You were asking about why some were 3/4" and some were 1/2". That was a rough explanation as to why.