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JamesNY 10-08-2010 08:01 PM

Reworking Radiant Heating Zones. Does this look right to you?
Thanks for taking a look. Please see the linked PDF drawings, and tell me if I have overlooked something important.

Existing Design (PDF)
Proposed Changes (PDF)

The existing design has two zones with excessively long 600' loops of pex hung between joists with plastic Wirsbo pex-clips. The tubing sits in a 3" airspace covered with only R13 batting (no foil). The major flaw I see is the continuous loops which should be no more than 300' long. Even at full boiler temperature, it is not putting out enough heat.

Proposed changes would use aluminum Joist-Trak on three 200' loops each, balanced with Mr Pex manifolds. R19 would fill the joist cavities. I plan to use one of the existing circulators as a primary pump, and feed two secondary loops from it, with 1" copper. The temperatue of each secondary loop would be controlled by hand-set thermostatic mixing valves. Using the ADS software I've determined the loops would call for about 97 degrees.

So, each thermostat will control its respective secondary loop circulator. But either one will also trigger the primary loop circulator and fire the boiler.

1) Is the location of primary loop circulator acceptable downstream from the secondary branches as shown?

2) Could this type of setup lead to short cycling the boiler?

3) To control the new setup, can I use a spare two-zone Taco control box? It would recieve the signals from the two thermostats, and switch on the secondary loop circulators. The relay output from that 2nd box (which is normally used to fire a boiler) would instead provide signals to the existing Taco box, controlling the primary pump and boiler. Am I missing something?

I understand that without motorized mixing valves that I might lose some efficency from the lack of automatic seasonal reset. Any advice is greatly appreciated.

beenthere 10-08-2010 09:00 PM

Your new set up. Will have the loops on the right of the drawing. Pulling in the cooler return water from the first loops on the left. When both zones are calling.

JamesNY 10-08-2010 09:26 PM


I had thought that with the boiler temp at 160 and the loop temps at 97, that it would not matter - as long as the water downstream of the first loop was still above the required temp of the second loop.

Do you think I aught to re-design the secondary loops to be in parallel with each other, instead of in series as shown? It would eliminate one of the mixing valves (which should be alright since both loops are expecting the same lower temperature).

Or do you suggest separating the loops entirely?

beenthere 10-09-2010 04:21 AM

After the boiler temp is up. And the loops are warm/hot. It won't hurt. But on the those days that the outdoor temps are mild. You would notice a temp lack in those areas.

Having both loops off the same mixing valve would work better. As long as both need the same water temp.

I'm guessing your using circulators with internal flow check valves.

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