I'm building a closed loop infloor heat system using a 40 gallon hot water tank. Wondering if the expansion tank should be on the hot side or cold side. I've seen different answers but I'm leaning towards the hot side. Anybody have thoughts on this? Cheers
Expansion tank placement
- Thread starter Bangon61
- Start date
Kezorm
Well-known member
Ditto Jackfre. Expansion tank is constant pressure point in system. Circulator should pump away from this point.
Air eliminator should generally be at highest temperature / lowest pressure point in the system.
Caleffi has some great technical literature on hydronic systems. Lots of good content on YouTube from Caleffi and Taco as well.
Air eliminator should generally be at highest temperature / lowest pressure point in the system.
Caleffi has some great technical literature on hydronic systems. Lots of good content on YouTube from Caleffi and Taco as well.
fitter30
Well-known member
Piping diagram Sprirotop for a small system won't be needed. Ex tank air pressure same as room temp water pressure system pressure. Use only a tire pump and a low pressure tire gauge.
Kezorm
Well-known member
No. This sounds like your planning to pump towards the expansion tank. You need to pump away from the expansion tank.
I'm pulling hot water from the hot water heater, past the expansion tank into the floor. Where it comes out of floor will be the pump ,pumping the cold water back into the hot water heater. Is that not correct?
Kezorm
Well-known member
No. The expansion tank should be at the inlet of the pump. Pump away from the expansion tank.
Kezorm
Well-known member
Is arrow pointing towards pump correct? Or should this arrow be pointing the opposite direction. With assumption that this arrow should be turned around, you are pumping towards the expansion tank, not away from it. Inlet of the pump is lowest pressure point in the system. You want the expansion tank at the pump inlet to maintain constant positive pressure there. Almost all of your head loss will occur in the radiant tubing so, as drawn (and assuming arrow other way), the inlet of the pump will be at significantly lower pressure than the expansion tank.
You want the air eliminator on the outlet of the tank with the feed to the bottom of it with the pump after .... the circulator will be on the hot side pumping towards the floor.
You also want to have a valve before the air eliminator so you can close it to power flush the system of air -- water heaters often hold a bubble at the top.
A T with a valve at the top before this valve will allow simple flushing
You also want to have a valve before the air eliminator so you can close it to power flush the system of air -- water heaters often hold a bubble at the top.
A T with a valve at the top before this valve will allow simple flushing
Yes the arrow should be turnd around and pumping into the water heater. Oops.
Like everyone else said, put the pump right next to the air scoop/ expansion tank (and pressure reducing valve) with the pump downstream. It doesn't matter that much if it is on the supply (hot) or cold (return), but it is slightly better on the hottest part of the system. Also, instead of an air scoop, I would recommend something like a Spirovent and instead of a water heater, I'd recommend a boiler.
So here is a better drawing of what I propose. Of course there will be some valves and hose bibs added for filling. But this is my general idea. And yes im using a hot water tank and not a boiler. Thanks everyone for all your knowledgeable help. 
Kezorm
Well-known member
As has been said multiple times, the expansion tank goes before the pump. Two options based on drawing you provided - move the pump or move the expansion tank. Of the two, I would prefer move the pump. Air eliminators belong at the highest temperature, lowest pressure. Expansion tank is lowest pressure point in the system. Outlet of water heater is hottest point in the system. So, keep the air eliminator and expansion tank on the hot side and put the pump immediately after. Pump away. Also, as someone else suggested, recommend Spirovent or equivalent rather than air scoop. Can be far more effective than air scoop.
Last edited:
Kezorm
Well-known member
Suppose there might be some small effect on water temp through the pump in theory. But these pumps will go decades running hot-side with baseboard temp water (160F+). Radiant floor water temps are certainly nothing to worry about.