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[wormmister]

What's all needed to control the temperature for in floor heating?

[RSI]

A thermostatic mixing valve is usually used.

[wormmister]

What about electronics and a separate pump.
Not so much as in floor heating but under floor heating from my boiler.
Was wondering what is evolved in setting this up.
Do I need a separate pump?, and what kind of controls?
Very new at this but pretty handy for a guy with only one hand.
1st year with my boiler. Hx in forced air oil furnace and a 30 plate hx for dhw a manifold.
Thanks for any advice.

[NaturallyAspirated]

What about electronics and a separate pump.
Not so much as in floor heating but under floor heating from my boiler.
Was wondering what is evolved in setting this up.
Do I need a separate pump?, and what kind of controls?
Very new at this but pretty handy for a guy with only one hand.
1st year with my boiler. Hx in forced air oil furnace and a 30 plate hx for dhw a manifold.
Thanks for any advice.

In floor and under floor are two different animals.  You want maximum temperature for under floor, and a mixed down temp for in floor (85-120* water temps usually).

If you want your under floor zoned on it's own thermostat a separate pump is the best way to go.  I think you may want to just put a couple closely spaced Ts after your DHW exchanger, and run the pump off the floor thermostat. 

See page 61-62 in Idronics #19 from Caleffi:
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_19_na.pdf

 

[wreckit87]

If said floor's manifolds are higher than the top of your boiler, elevation wise, do not pipe it into the boiler loop without a plate exchanger or you may have air issues. Even if it's lower, I would still pipe it as a closed system via an exchanger to keep the loops clear of oxygen and run said exchanger in series after the DHW plate if possible. If only one zone, a simple zone circulator that turns on when the thermostat calls will do well, either with a 120V thermostat or a switching relay to transform 24v stat power to 120v to run the pump. Boiler temp water will almost always be too hot to stand on so you'll want a 3 way, thermostatic mixing valve regardless to bring it down to the 120-150 range, depending on finished flooring.

[E Yoder]

Water temp used in an underfloor system really depends on how much contact the piping has with the floor. I've found if it's completely suspended you can run full temp water, you basically are using the hot air space as the conductor to spread out the heat. As the contact increases (heat transfer plates, etc) the water temp has to drop or floor temps go way too high. Tempering valve as was mentioned.
I've always plumbed it into the main loop with two close tees and a purge valve inbetween the tees. Spring check valve on the return to prevent ghost flow. Having a pump in an open loop a lot higher than the outdoor furnace can be troublesome, I agree.
Just my experience.

[wreckit87]

I did see a suspended system in a customer's house last fall that he installed himself but hired me to connect everything and pipe everything in the mechanical room. I initially didn't put a mixing valve in because I was certain he'd need 180 to bust through his 7/8" subfloor and pad/carpet on top in the living room, hardwood in the kitchen. That turned out to be a mistake, as the kitchen floor was literally impossible to stand on and the carpet was even uncomfortable. Piped in a mixer afterwards and the last I heard from him he was running 135 through it. This was a 4 story house so it was a closed system. Live and learn I guess

[juddspaintballs]

I'd love to see some pictures of that installation if you have any.  I'm particularly interested in the homeowner's part of the installation.

[wreckit87]

Sorry, I have none. I do know it was TJI joists with 1/2" pex stapled to the side of the top TJI plate with crowfoot hangers, and then 2" EPS foam between each joist just below the top plate so there was a 1.5" air space between the foam and subfloor. There was 1 pex line in each joist space.

[wormmister]

Ok
I'm ready to do this.
What size or type of pump ?
Do I need flow control valves ?
It's not above the boiler.
I have one 250 foot run and would like to add two more 250 foot runs in the future.
Here a pic of what I want to do.
Sorry for all the questions and the bad pic.
Using heat transfer plates.

[E Yoder]

The way it looks the mixing valve is oriented wrong .. I think?
Mix outlet should feed into the manifold.
I would suggest a 3 speed or variable ecm circulator so you can adjust flow as you add loops.
Grundfos 15-58, alpha, etc.
B&G has a Vario but I haven't used it.

[wreckit87]

I agree with Yoder. A typical mixing valve has the hot and cold ports opposite each other with the mixed out the bottom, opposite the knob. That should serve the supply manifold. Also, the mixing valve needs to be upstream of the pump. Pushing water into the valve holds the cold passage shut and short circuits hot water so you want to pull through it. I'm no artist, but something like this.

As for the pump, I typically use 3 speed Grundfos 15-58FC on systems like this. First gear is a little heavy for a single loop but will be just perfect for 2 or 3. Alpha 1 would be a good choice also as they draw considerably less power and will adjust themselves for precise flow, but they do cost twice as much. I usually only use Alpha pumps on multi-zone systems with zone valves so the pump can adjust flow when each zone valve opens or closes. A system like yours will do just fine with a regular 15-58FC or B&G NRF-25