Radiant not radiating

Dave H_2

Delta T.

Sending out 165 and coming back at 120. Like ME said, its either the heat loss is too large or the circ is too small, which is exactly related too each other.

Remember gpm = BTUh/delta T x 500

Adjust one of those values and it messes with all the rest.

But of course the only way to use this formula to remedy your situation is to "Do the Math" and you can never, ever be wrong.

Anthony C.

I'm firly green (green horn that is ) at Radiant heating, I know the basics but the troubleshooting I'm still tryin to figger, being an apprentice and all. I recently did an install in a small cottage about 600 sq. ft. . The ceilings are vaulted to about 18' at the peak and the insulation of the structure is O.K. at best I used a Biasi wall hung combi mod/con unit for my heat source-propane. I did a staple up install with heat emission plates on the perimeter of the building for added heat around the areas of greatest heat loss. I ran four loops of 3/8" Viega tubing each loop as close to but not greater than 200' to a simple distribution manifold . I put a Taco 007 on the supply side of this manifold. The joists were insulated with first foil/ bubble insulation and then R-19 underneath that . Also left an airspace between the bottom of the sub floor and the top of the insulation.
My problem is the floor and the cottage are not heating . The supply side of the system was cranked up to 165 degrees !! and still no heat . The return temp. seems a little high to me around 120 degrees, is this right ?
One other note the installation manual on this Biasi unit calls for a primary/secondary pumping set up with a "Hydraulic Seperator". What the heck is a Hydraulic seperator, I piped it as a conventional Primary/secondary setup placing two tees about 4" apart with a separate circulator.
Any help will be greatly appreciated. Thanks

Norm Harvey

If your using extruded plates, theres no need for that air gap in the insulation,.. push that insulation right up against the tubing.

Are you reading floor temps with anything? An IR thermometer?

Also Im suspicious of your piping, could you post some pictures?

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Timco

I only use p/s on a mod con if there are to be different gpm requirements. Agreed, put the insul right up there with no gap, and post a pic. p/s wants closely spaced tees, not really 4" apart. (that should not be the deal killer) I have heated a few of my rentals' floors with a 6 gal electric water heater and wirsbo joist-trac with 1/2" h-pex and it works very, very well with 120* water. Sub floor was 3/4 fir with 1/2" backer and tile floor. Just R-19 stapled up tight for insul.

Tim

Jamie_5

limited plate use

It sounds like most of the installation does not have plates, just the perimeter, with the rest being suspended tube. If so, he needs the air gap for the insulation.

Without knowing the heat loss or floor covering, it seems hard to say that 165F supply temp is excessive, especially if the water is coming back 45F cooler. (From the amount of tubing used and the installation type, can we infer that the spacing is approx. 8" O.C.?) The cathedral ceilings add to my suspicion that this system will never have enough output; is there a lot of glass as well?

tim smith

How many sq feet of glass is in the house. Single or double

with 16 ft ceilings I am betting quite a bit of glass?? The 800 or so ft of tube he put in sounds like 8" centers to me or close. I would have calculated closer to 1000 feet 600 feet if 8" centers I think. 40 degree drop by the way sounds too high. What kind of pump do you have on system side. Make sure you loops are flushed out also. Good luck, Tim

Unknown

That delta T,,,

concerns me most of all. That's a pretty wide gap. I know 200' loops is ok for 1/2" but 3/8" I'm not so sure about.

Anthony C.

The tubing is spaced at 8" O/C . The cottage has 2 windows and 1 set of sliders ,all glass. The floor construction is 3/4" ply. with3/4" pine planks on top . There are no drafts in this cottage it is pretty tight. I never took a floor temp reading but it feels not even luke warm to the touch, I know I should get an accurate reading, I have to get a IR thermom. I weil try to get some pictures out but it is a very simple piping scheme, a simple loop off the supply and return from the boiler and another simple loop off that one for the radiant zone. As far as the spacing of the tees , that is what the manufacturer recommends.
Do you think the 3/8" tubing is an issue? Or maybe the capacity of the 007 circ.? I know there will be significant pressure drop across the manifold with the 3/8" tubing can this pump overcome this? Thanks for the feedback

tim smith

Couple more questions, are all your loops warm?? Any

chance you kinked 1 or 2 loops while putting in and they are restricted?? What outdoor temp is it where the place is located. What's design temp? Tim

Anthony C.

When I bleed the loops I get water flowing through so I guess there are no restrictions. The loops feel warm and even when I pull down sections of insulation the joist cavity feels plenty warm. It seems as if there is no heat tranfer occuring . The outside air temps are friggin cold, the cottage is in the mountains on a lake with the northeast side of the cottage where the glass and sliders are , exposed . BTW all windows and sliding glass doors are new energy eff.

steveex

If your piping is correct and you are getting warm water on the return side of your hoses, i think you must raise the temp. Your unheated area under bays maybe to cold, your spacing of tubing if 8" is to far. Temp 165 - 170 try first if still bad results 180.

steveex

PS 200 feet per circut is not an issue, have done it many times when we use to use 3/8 hose.

Plumdog_2

Vaulted cielings and glass

are killin you. Sounds like the heat loss of the structure is more than the floor can produce. You may need supplemental; like some baseboard or radiators or fan-coils. 3/8 tubing stapled-up is gonna be weak at best.

tim smith

Is it a vented crawlspace under the structure, again how cold

is it!! What are your low design temps where this is?? High ceilings, quite low design temp, moderate at best bldg envelope. You may not be able to get there from here. You may need supplemental heat... Not the end of the world but probably should have figured out ahead of time with proper design procedure.. Not harping just informing. Tim

Unknown

What is the space temp getting to?

That's a more important consideration than actual floor temp. Plus, if there are no restrictions and 200" on 3/8" is not a problem then I'd have to say you need more pump to move that water faster, The extra wide delta T says the water is moving too slowly.

Charlie from wmass

Pine is a wonderful insulater. it conducts heat far less readly than any other flooring. How are the flows controlled/balanced through the loops?

Anthony C.

No crawlspace full bnasement. Fully insulated very tight and warm ( warmer than usual ) even in the dead of winter. I cant get the space temp higher than 60 degrees.
If I have to crank up the supply temps to 180, wouldn't I be better off abandoning the radiant and installing baseboard? Just a thought I'm getting desperate here. I wasn't very diligent with the heat loss calc. I took a lot for granted especially with prior radiant installs which turned out fine. A big shame on me on my part. I think this time I'm learning the hard way. Oh well it will only make me a better technician in the future. Come Monday I will get back there and take better readings . Again gentleman thanks for the help!

Mark Eatherton

Back to ground zero...

Gotta start with a heat loss calc...

That large of a delta T indicates one of two things. Either low flow or MEGA load. Probably the low flow. Or a combination of both.

THe fact that the basement is extremely warm also indicates a lack of proper insulation below the RFH emitter. Rule of thumb is 5 times the R value below the heat source as you have above it. In your case, with wood having an R value of 1/inch, you have a 1.5 R value above the source, hence you'd need an R 8 below the source. You have R19 which should be more than adequate.

In any case, do the math first, or in your case second :-) I suspect that you are a victim of infiltration.

ME

Steve Garson_6

I had a similar problem with my own radiant install in my home. A larger circulator did the trick. I installed a 3-speed. I have cathedral ceilings, as well, and need the supplementary baseboard on the coldest days when the temp is below 10*.