Radiant floor return water too cold

GroundUp

@HomerJSmith I'm not sure why this is so tough to grasp. The manifold with the flowmeters in it MUST be the supply in order for the flowmeters to work. The fluid MUST exit the supply manifold through the loops. It is currently flowing the opposite direction, so the piping MUST be reworked to supply the lower manifold and return from the upper manifold instead of vice versa like it is now. No amount of changing valves is going to reverse the flow through the manifold. It is going the wrong direction through the manifolds and floor loops, so the pipe that leaves the bottom of the circ MUST be connected to the lower/supply manifold. The upper/return manifold MUST then be piped back to the return.

@Mkflyy yes, again, you need to repipe it. The flow needs to leave the circ and enter the lower/supply manifold. The flowmeters will never, ever work when piped backwards as it is now. Again, this may not fix the flow problem, but since you're repiping anyway, it would be ideal to repipe as primary/secondary as I stated earlier. And while you're at that, please switch to oxygen barrier tubing.

GroundUp

hot_rod said:

GroundUp said:

@hot_rod have you ever run into an Everhot manifold piped backwards like this? I'm not certain why, but the restriction is quite evident. Possibly holding the venturi shut? I don't know the science behind it but I do know that I've had several sets of these with similar issues and once flipped around, the flow was significantly increased. But yes, the pressure drop through this particular tankless is also pretty serious.

I’m just looking inside a Watts SS and a Caleffi. With them disassembled it just a hole through them. The valve and meter just screw the opening close. But I have not disassembled that brand to know for sure. The manifold correction is easy for the OP.
The heater may be not as easy. I’m Just suggesting the easiest attempts first.

I cannot say what the Caleffi looks like inside, but I have seen a number of Watts/Rehau manifolds piped backwards with no serious flow resistance. Obviously the flowmeters don't work, but I've repiped a few and the flow gain wasn't terribly significant. There is some change, but maybe 10-15% compared to 60-70% I've found with these Everhot/Rifeng/Bluefin manifolds. I also have some brass Zurn manifolds in my own shop that I piped backwards and in series with an electric tankless not much different than is done here, 15 years ago before I knew any better, and still see the same trouble because I have not bothered to fix it. Based on the 14.4kw output of the tankless and the delta T of my own system, I am seeing approximately .15 GPM per loop which lines up right with what the OP is seeing here. I only keep it 50* in there so it never has a problem keeping up even at design temps, but if I try to crank it up to 70* it'll run for days to get there.

hot_rod

I'd shorten the white pex 10" or so to match the upper manifold.
Lengthen the blue 10" or so to reach down to the lower manifold. Super simple fix with SharkBite fittings.
Either a 10 mm open end or an allen wrench to remove and flip the handles.

HomerJSmith

What the Everhot catalog says is balancing valves (see picture), I say are hard shut off valves. I think that the gauges are the balancing valves. You might want to see if the black caps over the base of the gauges can be removed and inverted over the gauges and the gauges rotated to set the flow as marked on the gauges. The white arrow points to the black caps.

I've always piped the flow into the gauges and not the hard stops. Just the reverse of how you piped the supply and return into your manifolds. Looking at your newest pic, I would leave the valves as they are, shut them off and switch the knobs and repipe the flow into the manifold with the gauges and the return to the boiler to the manifold with the hard stops. That way you won't have to drain the manifolds.

hot_rod

Both the flowmeters and the white caps can be used to balance. The white caps have two threads. One to thread onto the manifold, the other to make the small flow balance adjustments. They are stops, and also full open when completely removed.

The flowmeters adjust and can also be shutoff valves.

I think the flowmeters will only work with the proper flow direction. The OP mentioned they are not reading at all, in the current piping

At least on all the other manifolds I have used.

Their manual doesn’t show or explain the insides very well. Maybe there is some other flow restriction inside the ports as @GroundUp mentioned?

HomerJSmith

This is the way I would do it. Turn off the valves to the manifolds-switch the knobs-lengthen the supply pex to the lower manifold-lengthen the pex from the upper manifold to the white return pex to the heater.
Can I ask you how you fill the system with water? I don't see any fill valve in your photo. How do you regulate the pressure in the sys? When you fill the heater sys the air in the lower manifold would work its way up the the air eliminator unless there is a check valve in the volute of the pump (which check valve you don't need). The air in the upper manifold to the heater should have an automatic or manual air eliminator in the heater cabinet, I would think.
You have to get all the air out of the sys and let the air eliminator remove the entrained air. Make sure the vent cap on the air eliminator is loose. Go thru the purge sequence one loop at a time.
I hate to say it but this has all the hallmarks of a "do it yourself" installation. Perhaps, it would have been prudent to get advice from the great and wonderful professionals on this site in the planning stage.

Grallert

you could also just swap over the manifolds with out repiping. Am I wrong? it's been a minute.

HomerJSmith

No, you're not wrong, but it isn't the easiest way to do it, tho. There is also a consideration of how the pex is laid in the concrete. You would want the hottest water going to the perimeter and the cooler return to the center of the slab. Is the layout serpentine or concentric counter flo, etc. But the layout is cast in concrete, what is, is.

Jamie Hall

Not an expert here by any means -- but some types of flow meters have a movable body in them which is resisted by a spring. Flow through the meter pushes the body against the spring, the distance being determined by the flow rate and the spring resistance. This type of flow meter will not register on reverse flow -- and will have a very high resistance to flow in the reverse direction, almost like a check valve. Could this be part of the problem here?