Basement Radiators

Stokehold

Hello!

I'm installing some cast iron rads in my basement on a direct return two pipe loop. Are any type of diverters or mono flows necessary here to force the water downward about eight feet into the rads? I know they are required in both supply and return in the one pipe loop system. Also, in the one pipe loop I understand that minimum pipe size to the rads must be no less than 3/4" regardless of BTU and flow requirements. Is it the same in the two pipe system or could I possibly use 1/2" to the rads considering the biggest one is no more than 11,000 BTU?

kcopp

Diverter tees and down flow can be pretty tricky. you are trying to make water do something it does not want to do naturally.
How many rads?
I would opt to do a manifold system 1 supply,1 return and home run 1/2" pex to each.

Stokehold

I have considered the pex but the basement is large and it would be a bundle. In the one section, I am planning four rads to accommodate approx. 1250 sq. ft area. This area is at the opposite end where the boiler sits 54 ft. away. The total basement is over 1764 sq. ft. I am not sure what is going in that smaller section yet. I should mention here that this system is supplemental and for the basement only. Anyway, if I did the pex, that would be eight 1/2" lines running a minimum of 54 ft. and probably a maximum of over 70 ft. The total load of the rads doesn't exceed 38,000 BTU. I was originally hoping to run a 3/4" reverse direct return and plumb the rads with 1/2". This would have certainly kept the price down if using copper. If I am not mistaken, 3/4" can carry 40,000 BTU at 4 gpm. I felt that this would work until further research dictated that a one pipe system with mono flows still needed nothing less than 3/4" on down flow connections, so I assumed the loop itself may need to be 1". The price starts to really go up from there. Would I be better to just plumb these rads in series? I know they won't heat evenly, but they are in the same room, more or less. That would definitely make things simpler.

kcopp

Don't pipe rads in series. The manifold set up will work and it will be faster....and you wont have to futz around w/ bleeding.... time is money.

Stokehold

I have to admit, I have no experience with pex. Are you refering to pex-al-pex? The limited knowledge I have says IT IS the easiest, fastest and cheapest way (not necessarily the prettiest) but all plastic is not equal. This boiler, by the way, is fired on anthracite coal and there is always the chance for temps to exceed the 180 high limit. There is a dump zone to get rid of excess heat just in case but I have some doubts about plastic and high temps. I guess I am too old school. Anyway, tell me exactly what type/brand pex is the best for boiler applications.
Thank you for your comments!

kcopp

I use Uponor pex.
Coal boiler....hmm . If that's the case it could run away. I would be wary.

Rich_49

You state that temps can exceed 180* , do they normally hover around there ? Put the manifold in a remote location closer to the rads and run 1/2" to them .
PAP is the way to go and as KCopp mentioned , Uponor is of the best quality . Pex does not have to look like hell , although most seem to tolerate it because it is Pex . Strap it right , make it nice and don't be embarrassed to tell your friends you did it .

Stokehold

That was going to be my next question about manifold location but you already answered it. This is starting to make a little more sense. You know, when I bought this place I completely redid the domestic water and after nearly three hundred ft. of pipe, mostly 3/4", 21 ball valves, over one hundred various elbows, tees, couplers and unions, the guy who was helping me with the geo unit brings in a piece of Uponar aqua pex and a special Milwaukee tool. In about 10 seconds he expands the pex, slides the fitting in, and done. He then bent and kinked the tubing then applied a small amount of torch heat to it and like magic it regained its straightness! Considering not only the cost, but the work of cutting, deburring, cleaning, fluxing, heating, sweating and more cleaning, I was really starting to feel stupid. The cost is not only a factor, but the time is more important. Albeit, that copper job was as pretty as a picture. You guys seem to know what you are talking about, now if I can just break my old timer view of plastic on boilers...
Thanks again for your comments!

Stokehold

One more question. If I use PEX for this install, is it possible flow problems could still develop at the manifold considering I am trying to pump hot water downward? What I mean to say is it possible that the water could leave the manifold and only travel through one or two circuits instead of all four? This comes back to my original question on a two pipe direct return. Wouldn't the supply header be similar to a manifold since it is larger, 1", than the 3/4" piping to the individual rads?

Ironman

With a circulator, you have a forced flow system, not a gravity flow. As long as you use a manifold, the system will be piped in parallel and what's pumped out through the supply, must come back through the return.
Use a good manifold such as Rehau or Caleffi with flow setters, not the Chinese junk. You get what you pay for.