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Circulator pumps. On the supply or return?

Sopuzzled Member Posts: 5
Hi Brad,

I'm a home builder in Pa. building one for myself this time. Just before pouring I decided to install in floor heat to the basement slabs and a wood fired boiler, I'll figure the rest out later! (Wirsbo did the zone calcs) 27 months, later is now! In slab zones are in, heat exchangers are installed the 2300lb boiler is in place and it's time to plumb everything in. E-Ha! After digging in to "what’s next?" I see there is more to this than I originally thought! Pump sizing for head and flow, Air eliminators, Expansion tanks and the like.

My primary boiler loop goes to a 120 gallon buffer tank that all zones will then feed from. The circulating pump was factory installed to push the return water through the boiler. I assume I should move the furnace call for heat aqua stat to the buffer tank. That stat controls the motorized damper and low water cutoff. I did learn where to install all the main boiler controls along with an emergency dump zone for power loss events, didn’t see that in the brochures!

I start to loose my way feeding the zones from the buffer tank. I decided to use a circulating pump for each zone and control them with a pump controller.

Should the pumps be set to push the hot or the cold coming out of the buffer tank or Some pushing and Some pulling I’ve seen that arraignment in drawings also.
I see I need to temper the water for the slab zones (90 to 110?) also… I see the mixing valves to temper the water need to be installed on the suction side of the pumps to avoid damage and I’ll need a temp gauge for each slab zone… This is turning into a real tar baby! I don’t mind learning something new in fact I enjoy the challenge I just wish I would have started this 3 months earlier!

I stumbled here as I'm sure many more will with everyone trying to cut energy costs. For the DIY Bell & Gossett has a good primer on how radiant heating systems work for both open and closed systems. That site helped me gain the basics and show me how much more I didn't know about all this!



  • Newbee_2
    Newbee_2 Member Posts: 1
    pump which?

    I'm trying to understand radiant systems. Some schematics have the pump on the hot side and others on the(cold)return side?

  • Brad White_202
    Brad White_202 Member Posts: 105
    Not specifically

    to radiant, any hydronic system wants the circulator to be just downstream from where the expansion tank connects. This is often on the outlet side of the boiler, but if the circulator should be on the inlet side of the boiler, so too should the expansion tank be connected there, just upstream of the circulator.

    Now, when P/S piping is used, the circulator is often on the inlet side of the boiler to push water through the boiler for a more positive reaction to any internal pressure switches. (Many ModCon boilers have delicate positive pressure switches and high internal pressure drops which is why they need dedicated circulators. Not all ModCons, but many.)
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