GPM flow rate thrugh cast iron radiators

bob eck

will be installing a Triangle Tube PE110 Prestige Excellence nat gas boiler in a older home that has cast iron radiators first and second floor.

will be piping it primary secondary will be taking out large 2" black supply and return and using a radiant manifold and doing a home run of 1/2" VIEGA fostapex pipe direct to each radiator.

first off the manifold will be the 6 second floor radiators and then the 4 first floor radiators with the radiator closest to the thermostat last.

The manifold will have flow gauges on them and I will be able to balance each radiator so they all get hot at the same time. On the header the max flow GPM to each radiator will be 2 GPM will that be enough to make the radiators heat up and give off enough heat? 

Ironman

That Will Be Enough...

To get 20k at the rad, assuming you can get 2gpm to each one. I think the max you're gonna see with 1/2 pex and a manifold is about 1.25 to1.5 gpm per loop. Still, that would give you 12k - 15kbtu's on each loop.



Use an EDR table to determine the output of each rad. If you have any over 12k btu's, I'd run 3/4 in pex.



I've attached a recent thread on pump and pipe sizing.



http://www.heatinghelp.com/forum-thread/135487/tradeservices-tech

bob eck

GPM flow rate thrugh cast iron radiators

Each cast iron radiator will be between 5,000 to 10,000 BTU. I will be using a grundfos Alpha circulator. the system I now have with the large 2" supply & return is a old gravity system that is being pumped but the first floor gets warmer than the second floor and the thermostat turns off. by replacing large 2" pipe and running 1/2" fostapex direct to each radiator with second floor coming off the manifold first and the radiator closest to the thermostat first the second floor temp in radiators should be the same as first floor radiators. with less water in the large 2" pipes the radiators should heat up faster and with the water volume in the large radiators the boiler should still condense most of the season. will run boiler water temp going out to system on coldest days at 150*F or 160*F so system should stay condensing most of the heating season. . .

CMadatMe

Say Bye Bye

To the thermostat. Get rid of it. Add thermostatics to the rads and let them fly on the boilers ODR curve. Also don't pri/sec use a LLH. If you dead set on a thermostat then get in a centralized location. What's the heat losses in these rooms? 5 to 10K sounds rather high.

Brad White

May I add

A low loss header, (LLH) is another way to achieve P/S and frankly a neater way. It also allows a handy location for air removal and sediment separation, essential in an older iron system. (Iron and stainless boilers do not play well together; you want to remove as much as possible, another topic.)



Yes, the heat losses or rather heat outputs of the radiators seem high and the heat losses are probably, by experience, less. This is where tweaking your ODR curve pays dividends. Drop the temperature until you feel a tad under-warmed then bring it up a notch. You may also find yourself setting a higher baseline in warmer weather. (The month of March is cruel but useful!). Houses are like snowflakes. Your results may, or rather, will, vary.



The presumed capacity of those radiators is ideal for a PEX or PEX-AL-PEX home run manifold system using 1/2" or 5/8" tubing. TRV's on all of them and a variable speed Delta-P or Delta-T circulator will be a sweet system.  If the heat losses and actual demands are lower, your pump energy might well be under 20 Watts, likely less and sometimes the single digits. Cool.



I should also add a totally uninformed note about your expected required highest temperature. Uninformed because I know nothing about your heat loss and radiator size relative to that. But from experience, you may find your "on paper" need for 160F water may well be 140F even on the coldest day. Constant circulation is one part of this, moving water all the time in heating season and gently varying the temperature. What is also something to work on is the flow rate.



Flow rate is a very forgiving variable- cut the flow in half and your radiator puts out not half the output but 90 percent.



Imagine this: Your base system takes water at 180F supply, 160F return and thus, 170F average, a 20 degree Delta-T.



Cut  this flow in half, your entering water is still 180F but your leaving water is 140F. Your average water temperature is now 160F, only ten degrees cooler. This typically gives about 90 percent of output capacity.



Why is this useful? Imagine your actual high temperature need is 150 after some tweaking, on the coldest day and your average is 140F. Great. Your return is 130, OK good efficiency but not quite there for good, consistent condensing.



(You need 122 or less to really get the ball rolling -with exceptions and variables of course).  



But say you can cut your flow by 33% and tolerate a slightly reduced average temperature. Now you send out 150F water, take it back at 120F. Your average temperature dropped to 135F, only five degrees. But your return water is 120F and you are far more likely to consistently condense even on the coldest day.



Such a deal.

Ironman

Orifice Plates?

Bob,



Sometimes the old timers put orifice plates in the 2nd floor rads of a gravity flow system because the water naturally wanted to flow upward to the 2nd floor before it would heat the first floor. The restriction forced more water through the first floor rads so the house would heat more evenly. When your system was converted to forced flow, they should have checked for these and removed them if they were present. This may be why your 2nd floor doesn't heat properly.

bob eck

GPM flow rate thrugh cast iron radiators

would the orifice plates be in the supply or return of the second floor radiators?

what do they look like? is it like a flat piece of metal with a small hole drilled into it?

when I had the old cast iron weil mclain oil fired boiler on the same piping going to all radiators right off the supply was a pipe that went to the second floor middle room radiator and when the first floor thermostat would turn off the second floor radiators would be warm but not as hot as the first floor radiators but the one on the second floor that came off the large 2" supply first always was the hottest on the second floor. 

Brad White

"What do they look like?

is it like a flat piece of metal with a small hole drilled into it?"



Yes. Tunstall Associates in Chicopee make them but many were hand made. For steam and for water too.

avid

Stainless and Iron Not playing nice? Please Elaborate

This thread exactly describes a current estimate I am working on.

I appreciate the quality of the dialogue.



I don't wish to hijack the thread, but was wondering if we could hear about the difficulties with a mod/con boiler and iron pipe. It seems pretty topical.



To control costs I was thinking about keeping the new pex in the basement and letting the pipe in the walls stay. I suppose sediment is going to be hard on the heat exchanger. How bad an idea is this?



I would love to hear words of the wise

CMadatMe

Low Loss Header

Using a low loss header/hydro separator would be the best approach. No worries. The HX would be protected. Attached is some reading..