Radiant Joist

KeenGreen

I have just completed a heat loss/system design for a customer of mine. He will be using the radiant joist system to supply heat to the main and upper floor of his house. My design program has suggested some really high temperatures for the floor (150 deg F using an r-value of 1 for the floor) Is there a maximum temperature that can be supplied to the Radiant Joist system?

Thanks
KeenGreen

heathead

Is the design program using heat emitter plates ie ThermoFin. Or just using staple up for tubing?

KeenGreen

Yes. Aluminum plates by Heatlink. 24" long x 4-1/4" wide.

Jamie Hall

I hope that is the temperature of the source water, and not the floor... I'd never, ever, run a floor surface temperautre over 80 to 85.

Rich_49

What is the floor build up ? Plywood / hardwood ?

Ironman

I never design above 120* SWT to an under floor system with plates. That being said , I did have one where we had to recalculate because the builder used 2 x boards on top of 3/4" Advantech. I called their engineer and he said their product could take any temp below 450*.

The two main considerations are surface temp (as Jamie said) and what temp can the wood being used withstand. Surface temp should not exceed 84*. The wood temp will very depending upon type, width, thickness, etc.

If you can't get enough btus from the floor to meet design requirements, then I'd recommend that you add some form of supplemental heat where needed.

Ironman

KeenGreen said:

I have just completed a heat loss/system design for a customer of mine. He will be using the radiant joist system to supply heat to the main and upper floor of his house. My design program has suggested some really high temperatures for the floor (150 deg F using an r-value of 1 for the floor) Is there a maximum temperature that can be supplied to the Radiant Joist system?

Thanks
KeenGreen

I just saw in your other post that you're in the Vancover, B.C. area. I was there about 20+ years ago. That said, I don't think that you have that low of a design temp compared to most of us.

If that's the case, you shouldn't need that warm of a SWT for the floor. If you don't mind sharing you design criteria (tube size, length and spacing; heat loss, sq. footage, number of loops, etc.), we would be happy to see if there's something that's needs tweaking.

RomanP

I just checked out heat link plates and it’s a direct heat transfer plate. I’d say 150 would be a bit too high. I used ones by zurn( I think) which is a better product, imo, the aluminum is much thicker I ran the floors on 130-135 degrees. Had 3/4” subfloor and 3/4” quarter sawn hardwood. I could see underfloor suspended system, aka Ultrafin being ran on 150, since it’s not direct heat transfer....

Maybe your heat loss is too high for that square footage and that’s why the program calls for 150 SWT? I did radiant in addition which was a sun room, on slab, three exterior walls made out of windows, cold roof as well. My software called to 190 SWT lol or 200 or something like that. At first I almost went with that idea, but figured client was a great guy and I did want them to enjoy the room and added 10’ copper baseboard.

And yeah... what @Ironman said. If you could share some numbers that would be nice

Thanks

newagedawn

its always hotter water when doing under joist radiant, need more heat to penetrate through the floor, i am not a big fan of this style turns the house into a piece of kindling by drying out the floors

Zman

@KeenGreen
Please share your calculations.
150 is high for an aluminum plate application. Looking back at similar projects, they run pretty well in the 120-130 range.

KeenGreen

Here is the info......
Tube size is 1/2"
Tube length - Varies room to room
Spacing - is in joist - 8"
Heat Loss - total is 69618btu's
Square ft - 4000 sq ft
Number of loops - 20
Supply temp - 130F
Floor design Temp - 72F

Ironman

So your AVERAGE heat loss per sq. ft. is 17.5 btus. With 120* SWT you should see about 20 btus per sq. ft. output. Speaking off of the top of my head, but I know that's very close.

What's the longest loop length?

KeenGreen

Longest loops is 266'

Ironman

Then you should be okay with 120* SWT. Again, that's on average. Any particular room may need more. Did you do a room by room heat loss calc?

KeenGreen

@Ironman Yes full heat loss. room by room calcs.

Ironman

Do any of the rooms require more than 20 btus pr. sq. ft.?

heathead

Are the temps higher because it is thin plate?