Redoing Hot Water Radiators - Whats Ideal?

[LittleFatDog]

Well I gutted an old house and removed a whole lot of rusty iron pipe connecting a dozen or so old radiators.
Now that I have a chance to redo the whole system ( I will only re-use the radiators, everything else will be new) I want it to be purrrrfect.
I read both Pumping Away! and A Non-Engineers Guide to Radiant Heating - both by Dan Hollahan ( I think?) - I learned a lot about the history and dynamics of radiant heat. Still I never got a feel for the construction side of things, just the mechanics and design.

So I wanted ask about actual materials - would the ideal hot water system be a two-pipe, all copper, all sweat-fitted ticket? Red or Blue matter?

lfd

 

[Geniescience]

both good.

there aren't enough hard factual disadvantages to warrant ruling out one or the other. I might avoid copper. I know how to build with copper. That is just me and my preferences. I might use Kitec 3/4" which has a huge ID. That is just me.

David

 

[Sponsor]

 

[LittleFatDog]

wow - i hadnt considered (a) pex. i did the whole supply side of the plumbing with it though (regular pex). using it would mean working from a copper manifold im guessing? the pump/boiler, etc would be set up like a radiant floor loops except each loop would just feed a few radiators... ? what kind of transition do you use into an old radiator?

 

[Jadnashua]

Pex works fine in low-temp radiant, but I don't think it is speced for the "normal" boiler temps (nominally 180-200 degrees). If you lower the delta T, you can't get as much heat out of the radiators, so without adding more, you probably couldn't do it with lower temps going to them.

 

[hj]

Pex

For heating use, you need oxygen barrier PEX, or IPEX with the aluminum layer. As far as whether to use a one pipe, two pipe, or loop system, it depends on how you want to control the overall heating characteristics of the system. For conventional radiators, a one pipe MonoFlo system is usually the choice. And using the words 3/4" PEX and "big bore" in the same sentence does not work.

 

[LittleFatDog]

well i'm back at the drawing board again. the building is now cut up into a few apartments and the heating system for the lower two floors is still a month or two away (the top floor is hvac with a heat pump)

so 3/4 apex may have an ID of about .8" - and they claim is suitable for temps up to 200 deg. still i dont feel too comfortable with the idea.

does everyone just go with black pipe? i dont like cranking connections, something about sweat fitting seems more trusty to me - but i wouldn't mind saving myself from the costs of copper.

the way the building was piped before was one large (supply) black pipe that ran the length of the building and one large (return) black pipe that ran parallel to it. both were in the basement, at a few points there were 1" branches off it to each of the 3 floors. it didnt look too good. the expansion tank was on the wrong side of the system.

these radiators are huge, some weigh at least 250 lbs, i think i might get away with piping 175 out and getting 145 back - even undersizing the boiler a little bit. i'm getting started on doing heat loss calculations but here is a little sketch of the logistic side of what i think i should do equipment wise.
thanks for sifting through this.
lfd

 

[Got_Nailed]

If each room is not on its own valve I would put on at every radiator. Some rooms will need more heat than others. I would go with black pipe. I have an out side wood boiler and I’m using IPEX after my distribution valves. But I’m running a lower temp then the older boilers.

 

[LittleFatDog]

so why is it that nobody likes copper? besides price. i mean its flexible, durable and non-ferrous. whats the deal?

 

[TedL]

You may want to check out "The Wall" at heatinghelp.com.