OWB Vertical lift with extremely low gpm's issue

rustic

So I have an outdoor wood boiler (heatmor 200), 1" pex supply and return with a 60/40  water to proprolyne.  About 80ft from boiler to manifold. I have four 1/2" 250' loops in slab on grade 2" pink under entire slab. 1 grundfos pump of 1/6hp at boiler supply line rated with a max head of 29.  Supply line from boiler has a total of 13ft vertical elevation from the time it travels to the house up the utility room wall across the ceiling and down to the manifold. I filter installed. Boiler water runs around 180° and with the mixing valve i send it into the floor around 125°. Problem is my flow meters on my manifold dont even register. Temp sends back to boiler at like 45°.  cannot really get any heat into the floor. Tho it does circulate, just dont think its fast enough. I was told a 1/25 would be suffient, but could not even push the water, so i went to the 1/6 hp 3speed and still having issues. Do i still need a bigger pump? Maryjane another? Is my vertical elevation too great for the pump? Lines and 1-1/4" plumbing are not restricted. Everything is new except for the older boiler. 

hot_rod

You need a circulator after the mix valve before the manifold. That pumps needs to pull the blend of hot and cooler return to mix properly. The pump overcomes the flow resistence of the mix valve also, they have small passageways inside.

Remove any check valves and strainers at the H and C port of the mix valve

How do the supply and return pex to the manifolds connect into the OWB?

rustic

They are connected directly 1" pex to the 1 1/4" supply and return ports. No check valve at return just the pump has a check valve. See pic

hot_rod

Here is a simple solution. Loop from OWF comes into the building and goes right back out. Think of this as a heat conveyer belt

Two tees connected into that loop to pull heat from the "conveyer". Keep the tees 6" or less from one another.

A 3 way mix valve, an air purger, the pump.
On the return a ball valve with hose bib for purging.

Yo need two pumps, the conveyer belt loop, and the radiant loop. It will not work with just one pump.

Jamie Hall

With regard to 'lift" -- in a closed system, such as yours, vertical differences are taken care of by the static pressure in the system -- not the circulator. But as others have said, you need two pumps...

leonz

The cooler water returning to your forest eater is fighting against the water weight in the boiler.

Make sure you remove the check valve in the existing circulator when you install the second circulator as well.

hot_rod

If you have heat emitters above the water level, you do have some “lift” the first time you turn on the pump. Water will stay up in that circuit as long as you don’t allow air into it. Then the circ is in closed loop and just overcomes piping friction.


Under some conditions you can boil and flash to steam in upper sections, when the pump stops you have negative pressure.

GroundUp

There's nothing wrong with that circ, the radiant is piped wrong. At the bare minimum, you need a constant loop from the OWB and back with a couple closely spaced tees to your radiant using an additional circ pulling from the mixed port of the mixing valve and pumping into the supply manifold. To do it correctly, you should separate the two systems completely using a heat exchanger and have the radiant be a pressurized system.

Ironman

You’re gonna have constant problems with the radiant floor being directly connected to the unpressurized OWB. You need to put a sufficiently sized heat exchanger between the two systems and the necessary ancillary components to pressurize the radiant floor.

Then, as mentioned, the pump for the radiant needs to pull through the mixing valve and pump into the manifold.

I do these OWB systems all the time and if you’ll p/m me, I’ll give you a diagram.