MZ boiler piped to CI rads w 1/2\" pex

John MacGregor

I have some questions regarding my system.My 1830's house is heated w/an Mz 40 140,000 btu condensing boiler. House/system info:
I have CI rads that were fed with 1/2 pex, all home runned to a manifold. Piping system to me seems to be "parallel", in that the supply pipes come out and branch right away into supply manifolds, return lines do the same thing.

There are three vertical manifolds, one for every floor.
Heated areas are-basement, 1st floor and 2nd floor. Currently I have only one zone for entire house, run on constant circulation, as well as IDHW. There is a Grundfos 15-58 on the supply, and the 15-42 that comes with the boiler on the return.
Heatloss is 96,000 btu. (planning large addition so went w/140k mz).
I have been able to heat the house here in SE Pa w/ water temps of 135 degree w/out a problem. Return water temps are about 110 degree.
The problem I have is that the higher rads in the system, esp. ones that are furthest from the boiler, dont heat quite as well. (the return lines are much much cooler than the ones closer to the boiler)

The plumber that did it for me didnt do any calcs in terms of pump sizing. How can I find out how to do this (as I am assuming that I have flow problems)
I have done a room by room heat loss, and Edr of rads matches heat loss very closely. One of the second floor bedroom rads is a bit small in terms of matching btu output to heat loss, but still seems cool even when I crank water up to 160 plus. I have purged each rad in the system and have an air elim. also.
Thanks!

Mark Eatherton1

The three stooges do hydronics....

Wet, Lazy and Stupid, not Larry Moe and Curly.

The water is following the path of least resistance (Lazy). All it really wants to do is get back around to the pump and take another ride WHEEEEeeee.

The longest route poses the path of greatest resistance, and unless you tell the water where you want it to go (Stupid), it's still going to follow the path of least resistance (Lazy).

Give it credit, at least it knows how to be wet:-)

You need to balance the circuits so that they all see essentially the same approximate delta T (differential in temperature).

If you want to look at it hydronically, go to www.hydronicpros.com and down load their free trial software. You can then model your circuitry, and see exactly how many guppies per minutia (GPM) your circuses are flowing.

Glub lick!

ME