Boiler temp after emitter installation

HelpInAK

I’m a new homeowner with a cheaply installed subfloor radiant - staple-up pex with no transfer plates. I’ve got extruded heat plates on order with the goal of getting my operating temps down to condensing levels. What I’d like to figure out now is what set point temp I can expect to dial down to once installed. I’ve done some playing around with several heat loss calc applications and really don’t trust myself to get this right - I’m wondering if I can bypass all this and kind of work “backward” from my current space heat set point of 166F. If I am assuming the radiant installer did the heat loss calculation correctly to determine that 166F temp is needed to heat my house with staple-up, would an expert here be able to ballpark a temp I can come down to with the plates installed? Thank you!

Gordy

You will also need to insulate the joist bays once plates are installed.
Hopefully you got good plates extruded with omega style channel for pex.

hot_rod

A few steps involved to get an accurate answer. The room by room heat load first.
Then determine the available, un-encumbered floor space in each room, that becomes the "radiator" Some rooms may not have enough floor space to cover the load with just the radiant floor, figure about 25-27 btu/ sq foot as reasonable for radiant floors.

Assuming you have enough tube in each room or area, and enough boiler horsepower, adequate distribution and pumping power, a WAG would be under 140 SWT to cover the loads.
Radiant Engineering has nice output charts based on the floor build up. Get rid of any thick carpet and pad!

Most manufacturerd wood products, plywood, waterboard, etc, will have a temperature limit to prevent outgassing or material breakdown, so be aware of just cranking up SWT to offset a bad installation and design.

HelpInAK

@gordy the joist bays are currently insulated with R-19 under the tubes. I’ve also read some sources that say to install an aluminum reflective barrier between the tubes and insulation. Is this generally recommended by all?

@hot rod_7 Let’s say I install the plates and arbitrarily set the SWT to 140. What indicators would let me know that it’s “working” for me? What difference would I experience at 140 vs say, 120? And would I be risking damaging anything by experimenting with different set points here?

Gordy

In my opinion the reflective barrier does nothing but cost money. It’s going to get dusty, and that takes away from any possible radiant insulation benefit.

What type of boiler do you have?

DZoro

I would go with the aluminum barrier to help seal a tight cavity, 1/2 - 1" below the tubes. Then R-19 under that.
To possibly help you with some water temp numbers. My system is designed the same way. I run a Lochinvar Noble with outdoor reset set -20*F @ 128* water cold day, constant run pump.
We just got out of the Polar Vortex temps went down to -32*F. Our house stayed at 68*. Remodeled home R-55 attic, R-28 walls, stone foundation basement.
D

Gordy

In the end it's as simple as dropping water temps a little at a time until set point isn't being maintained. Each adjustment should be given time to reach thermal equilibrium.

If you have a mod/con boiler it's crucial to get those return temps into condensing range as much as possible. To get the highest efficiency. Hopefully you have outdoor reset control installed. This will adjust the water temperature based on outdoor temperature.

If it's a cast iron boiler then you can only go so low as you don't want to condense at the boiler. If you do have a CI boiler then a boiler protection strategy should be used to protect the boiler.

Gordy

Also when installing those plates make sure they get good contact with the sub floor. Conduction is king with radiant heat transfer.

HelpInAK

Thanks all. The boiler is a Lochinvar noble NKC199. Unfortunately no outdoor reset, I’m working on getting the original installer back out here to finish the job. I’m going with the plates pictured, specs and price seem to be on par with some name brands like the Uponor joist trak, but these plates are the only ones I can get shipped to me without costing an arm and a leg.

hot_rod

that boiler should include an outdoor sensor, can you get it and a wire to a north side wall, overhang, etc? Having reset control will really smooth out operation when you get it dialed in. You can also derate the heating side if it is way oversized for the load.