The correct way to configure hot water radiators to be most efficient

Dong

I am in the process of of doing a first floor renovation which includes relocating and adding Sun Rad radiators. I will have a total of nine cast iron hot water radiators on one zone; {3} 10 section {1} 16 section {2} 14 section {1} 8 section {2} 6 section and a new Burnham ES2 boiler with a tectanium indirect hot water tank. I am looking for advice on the most effecient way to tie these in for even heat distribution, ie do I do a manifold running home run returns and supplies to each radiator, daisy-chain, or reverse return etc. ? I have a mechanical background, which sometimes hurts me because I put to much thought into it. I have asked a few different plumbers and had gotten different answers from each one, so herin lies my confusion. I don't mind spending the extra time and money because at the end of the day I want to be happy with the results and have sufficient heat.

hot_rod

Pros and cons to each piping method.

With home run you get the exact same supply temperature to each radiator, so sizing is simple. Determine room load on design day, chose the SWT for design day and look at the output charts.
It does take a lot of tube, 1/2" pex is usually adequate. TRVs give you more room by room control. A pressure differential circulator maximizes energy use. Out door reset maybe?

Series is simple piping, perhaps 3 or four on a loop.

Anytime the rads are in series you should calculate temperature drop and compensate in the sizing.

Some other options here:

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_19_na.pdf

mattmia2

Since you already have the radiators, unless you calculated for series, that probably isnt a great option. Standing cast iron radiators really dont have a way to balance them other than regulating fluid flow. Direct return, home run, and reverse return are good options. Reverse return has little benefit unless your mains are long. Direct return will save labor and material over home run and you you can easily balance with the radiator valves or add TRVs.

neilc

wonder if you could balance series rads by the amount of air in them

mattmia2

neilc said:

wonder if you could balance series rads by the amount of air in them

It is an interesting idea but if your air elimination is working the air should eventually find it's way out

Danny Scully

I wouldn’t consider series loop or direct return. I would choose between Homeruns or reverse return (reverse return is far superior to direct return). In choosing between homeruns or reverse return, with a single zone and 10 rads I would choose reverse return. You’ll need 3 pipes instead of 20 essentially. 

pedmec

i normally do home-runs with 1/2" pex and its worked without issues. The biggest is balancing but that can be accomplished at the manifold

Big Ed_4

"wonder if you could balance series rads by the amount of air in them".

Yes , you can leave air in the radiator to drop the output. Use it in a fix..

JimP

I’d favor reverse return piping. It’s simple and straightforward. Depending on how the radiator locations are balanced to the heat loss will determine how much you’ll need to tweak the balancing at each radiator. 

hot_rod

mattmia2 said:

wonder if you could balance series rads by the amount of air in them

It is an interesting idea but if your air elimination is working the air should eventually find it's way out

And it makes for a conflicted PONPC in the system. A bunch of expansion tanks throughout the piping system