Super-Simple Radiant v 3.1

Mike T., Swampeast MO

Hi-low memory thermometer shows 1.7° temp variance. Likely much has come when the door was infrequently opened. Steam shower so everything including door is completely sealed. Clear glass door and I can see the readout through the door and it's been nailed at 70.6° plus/minus 0.2°.

During this time outside temp has varied from about 23° to 60° with winds from calm to heavy and gusty both generally from the N to NW and S to SW. Shower has N & E exposures.

Temp in bath proper has varied from about 63° to 67°. Keeping it cool as I'm working in there and like to work in a cool space. Electric radiant floor in rest of bath set quite low. Haven't measured its temp or variability yet but my hand tells me variability is MUCH greater than in the shower.

Haven't remeasured delta-t across the shower loop nor touched the balance valves as there seems no need at current. Hand tells me that delta-t has increased a bit as has the general temperature of the walls in the shower.

Currently 45.7° outside and shower floor temp (measured at same point) 82.9°.

Remember this is simply tapped into constantly circulating, mechanically reset mains.

Two baths in house use same connection method but RADICALLY different heat transfer system. In shower it's 3/8" copper tube slid into 5/8" garden hose and embedded in the mud base. The other baths use 3/8" copper in Thermofin attached below the floor (plywood, cement board and tile).

The two baths have RADICALLY different exposures but wind up with nearly the same heating result--right at 5° above the temp of the spaces surrounding. They share a little reverse-return "manifold" and are nearly identical in construction.

Wish I could say whether what appears near-perfect success is coming from careful engineering, luck, or radiant "forgiveness". It does though seem rather apparent that the different heat conduction methods have the planned effect as the cement-embedded system is producing surface temps only a couple of degrees higher than staple-up but using the SAME water temperature.

For calculations I've used HVAC-Calc at 80% of computed value and the Rad Pad. Would venture to say that with tight new construction you could safely use 70% or even 65%.

I have had to make some "best guesses" regarding these unorthodox heat transfer methods. But nothing was particularly difficult or time consuming regarding the design.

When I first inquired about my design for "Super-Simple Radiant" here and elsewhere, was told, "Try it. The math sounds good but no experience with similar."

I sincerely feel confident in saying that if you are working on a system with TRUE constant circulation and outdoor reset with a ratio around 1.0 (mine is 0.9) that you can have similar success in smallish radiantly heated areas. Comfort is extremely high and the system is the ultimate of simplicity. You just have to CAREFULLY consider your CONDUCTION method of getting heat into the floor so that it works with your supply temp at outside design temp.

I'm sincerely going to try this in my kitchen as well. Quite large space about 500 sq.ft. I have 1" cypress, 3/4" plywood, cement board and tile to "get through" this time. Haven't done the calculations yet, but will probably pack three thermofins into each joist bay with some multiple of three loops as each joist bay will have a separate loop for each fin--should be easier to install with better balance over longer loops. Probably 2-3 years away...

Mike T., Swampeast MO

Wanted to wait 'til December, but had to turn on the boiler tonight. House warm but outside temp already down 30+° in 8 hours.

Careful bleeding measures due to construction seem to have worked as supply and return both hot within one beer of turning down the TRVs from full after initial fire.

Hand tells me that delta-t at startup is very low, as planned, but still have balance valves wide open.

Construction pictured below. Bleeders and ball valves (not shown) at BOTH supply and return with both bleeders on the "inside" of the loop. Simply tapped into constantly circulating, reset mains. Will post the surface temp tomorrow morning.

Mike T., Swampeast MO

Outside: 32° Wind: WNW about 8 mph

Supply temp at boiler: 125° avg

Delta-t across floor loop: 11°

Floor surface temp (see photo): 85.8°

Air temp in shower: 70° (Shower has about 11 running feet of outside exposure--north & east--and about 15 sq. ft. of glass block.

Air temp in rest of bath: 67° Bath proper has about 10 running feet of east exposure.

Delta-t a bit lower than planned and output/surface temp a bit higher, but overall space temp effect seems good. Will wait a while before adjusting the balance valves (currently wide open).

Mike T., Swampeast MO

What absolutely freaks me...

...is the way it takes DAYS for the exposed bath floor to get warm while the unexposed bath off the SAME manifold and with otherwise identical construction gets warm nearly immediately.

Once warm however, it STAYS warm as long as the system doesn't go into WWSD for a LONG period of time. It doesn't get cold during such--it just seem more neutral...

Sincerely thought I found an air bleeding problem that accounted for some of this strange effect but once I was as certain as can be that full and proper circulation was established everything worked just as "normal".

It's ALL about radiation!

hr

Tell me again

why the copper is encased in the garden hose? I wonder how much the transfer is compromised with the rubber prophylactic Seems you would have a air gap and an insulator between the connection.

Regardless, sounds like the results are meeting or exceeding you expectations.

hot rod

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Mike T., Swampeast MO

Why the garden hose...

1) Given the output achieved with copper in Thermofin in a staple-up arrangement I was quite confident that if I just embedded the copper in the mud that output would be WAY too high.

2) REALLY hard to find r-values for PEX. No source for a small amount of BARRIER PEX and no tools to make the connections. Am sure I could have overcome these difficulties without terrible cost, but even then was afraid of too much output unless tube spacing was increased more than I was comfortable with. I think you (Hotrod) replied when I asked about using copper with 18" spacing saying it was certain to have terrible striping. With the hose/copper used 8" spacing. If memory serves, it would have been about 14" with PEX.

3) Figured the best way was to somehow add insulative value to copper. Couldn't find a convenient and reasonably inexpensive way other than actually introducing a conductive "break" into the system. Used a heavy-walled 5/8" garden hose (Martha Stewart) and made best guess at it's r-value from measurement and published tables. Then added r-value of a small air gap. (Yes, I know it won't be continuous as the tube will be contacting the hose along an essentially random line). I posted all the assumed r-values here quite some time ago.

I presume the garden hose will deteriorate over time. How long I have no idea--maybe long after I'm cremated. Maybe well before. Something tells me though that crumbled garden hose will have about the same r-value as intact hose and air gap. The way I've made this shower I REALLY hope I'm dead before anyone has to tear it out to find the result

4) As a little "bonus" to this construction stresses on either the tube or the mud due to thermal expansion are eliminated.

To be completely honest I think that the r-value of the assembly is a bit higher than I calculated--thus the reason I haven't had to throttle the flow valves. But then again I'm CERTAIN that this loop has the highest pressure drop in the entire system and not knowing true flow amounts anywhere, I truly have NO idea of the amount of flow anyway...