unpressurized open/direct UFH with buffer tank heat source

[BuilderDan]

The following is a proposed very simple installation of UFH open/direct to an existing 1000 gallon fossil fuel hot water storage tank:

We are told that this won't work since the UFH pipework and pump are above the height of the tank, and therefore gravity will empty the UFH... But our reasoning was that siphon action would prevent this from occurring (since both feed and return will always be below the min level of tank). We have been advised to install a heat exchanger in the tank, and make the UFH circuit pressurized, but this seems unnecessary (and expensive for us). Does anyone have any thoughts, please?

 

[ShaunCorbs]

Can’t use ufh on solid fuel

May I ask why / what’s your plan ?

 

[BuilderDan]

it's just a little off-gird cabin, in the woods, in Alaska. So no rules and regs to follow...but obviously has to work. The HW storage tank is existing, and for the upper floor / mezzanine would be nice to take advantage of that HW with UFH. Thanks

 

[BuilderDan]

The only thing I would have to do is empty the tank one time and fit the send and return in the side

 

[ShaunCorbs]

How big is the cabin ?

 

[BuilderDan]

600ft2 (ish)

 

[ShaunCorbs]

A good log burner should heat that space no problem

 

[Chuck]

We are told that this won't work since the UFH pipework and pump are above the height of the tank, and therefore gravity will empty the UFH...

I think that the system might work okay to start with but would gradually deteriorate in performance until it reaches equilibrium with the pump and UFH air-locked and the levels in the risers matching the level in the tank. That's assuming you were able to get the pump primed and operating in the first place.

We have been advised to install a heat exchanger in the tank, and make the UFH circuit pressurized, but this seems unnecessary (and expensive for us). Does anyone have any thoughts, please?

An okay solution but you'd need an expansion tank, fill loop, air vent valve (auto or manual) and pressure gauge to complete the setup.

For a cabin in the woods in Alaska, I'd have thought that you'd want a system that was as standard and reliable as possible and to keep a set of key spares on site. I believe it gets pretty cold there in winter.