I have recently installed a radiant system between the floor joists of my new kitchen addition, and I cannot feel any heat coming up through the floor.  I can tell the water is circulating and the pipe coming from the heater feels hot.  I am using a 40 gal. hot water heater running at about 120F circulating through pex tubing.  The addition is about 185 sq. ft. and has two runs of tubing stapled in place between each 16" joist.  My kitchen flooring is linoleum.  I have used the foil-faced bubble wrap insulation underneath with a few inches of airspace, and then R-30 fiberglass insulation underneath that.  I cannot figure out why when I touch the floor I don't feel any warmth.  Any help would be appreciated.

Use an infrared thermometer to measure the floor vs some adjacent surface.

did you use aluminum plates? They would transfer alot more heat into the floor

What's the size of the PEX?
What is under that kitchen addition? Unheated crawl space?
What are the outdoor low temperatures?

No, I did not use aluminum plates.  But with all the insulation below it, wouldn't some have to radiate up?

It is 1/2 inch pex.  It is a somewhat unheated crawlspace underneath.  It attaches to my basement and stays at probably around 45F in the winter.  The outdoor low temps could get around 0F, but it is currently 35F.

Posted By cshaffer on 16 Jan 2012 12:17 AM
I have recently installed a radiant system between the floor joists of my new kitchen addition, and I cannot feel any heat coming up through the floor.  I can tell the water is circulating and the pipe coming from the heater feels hot.  I am using a 40 gal. hot water heater running at about 120F circulating through pex tubing.  The addition is about 185 sq. ft. and has two runs of tubing stapled in place between each 16" joist.  My kitchen flooring is linoleum.  I have used the foil-faced bubble wrap insulation underneath with a few inches of airspace, and then R-30 fiberglass insulation underneath that.  I cannot figure out why when I touch the floor I don't feel any warmth.  Any help would be appreciated.

How can you tell that the water is circulating?

No, I did not use aluminum plates. But with all the insulation below it, wouldn't some have to radiate up?

Yes, but it's probably not enough for you to be able to "feel" it, particularly if you are only using a temp of 120F. Other systems without plates can run at much higher temps, like 140F - 180F.

Is the kitchen itself staying warm enough?

These will explain why it’s not working and what should have been done:

See "Radiant Research" Kansas State University and Figure 5 from this link:
http://www.healthyheating.com/Boiler-efficiency.htm

see "In floor Radiant Design Guide: Heat Loss to Head Loss"
http://www.healthyheating.com/Radiant_Design_Guide/Infloor_Radiant_Design_Guide.htm

To repair at this point one or more of the following has to occur: the temperature of the fluid has to go up, the resistance of the floor covering has to go down and the conductivity between the pipe and floor has to be increased...

I can hear the pump running and the water in the return line is still warm.

No, I cannot get the kitchen up to the temp. I want it.  I have wood heat in the rest of the house, so some makes it's way into the kitchen, but even after turning the hot water temp. up to 140F, I still can't get the kitchen above 62-64F.  After turning the heat up I can now feel some warmth in the floor, but it still doesn't seem enough.

onward to 160!

Plates are looking pretty good right about now.

Yes, I just purchased one.  Depending on the varying temp. outside, after turning the hot water heat up to 140F, the floor temp. varies from 74-78F.  This is 12 degrees warmer than the floor in a room next to it.

Posted By cshaffer on 17 Jan 2012 07:01 PM
I can hear the pump running and the water in the return line is still warm.

Just wondering out loud. If the return is "still warm" with 140º water and the is substantial insulation under the pipe, where is the heat going? I would have thought the the return would not be much less that the supply if it has been running all this time. The space between the foil and the underfloor should be at 100 to 120 I would think. Is it possible that even though you hear the pump the warm return is just convection and that you still have an airlock? The 12º warmer than the adjacent floor might be because the room heat is being reflected back up by the insulation.

Just a thought.
Bob

Floor temp tells it all. output is surface temp minus room temp times 2, in BTU/sq ft. if he's 76 average floor temp in a 64 degree room that's 24 BTU/sq ft which is actually fairly high for a plateless staple up system. that new shiny foil must be doing something for him.

that also means the kitchen load is significantly over 24 BTUs/sq ft... not surprising, often, in a kitchen, but still a bit high. this is usually partly heat load and partly restricted floor area (cabinets) to blame.

Plates would definitely increase output but for a wood floor you won't want to go much above 30/sq ft anyway, typically... might be in a "need supplemental" situation here even with plates, depending on the desired final room temps.

Sorry, I shouldn't have said the return line was just "warm".  Actually, I have no idea what the return temp is compared to the outgoing since my heating contractor didn't install temp. guages.  I am going to have him come back and check for an airlock and maybe even install temp. guages.  For some reason my heating sensor isn't accurate when I point it at any of the pipes.  Thanks for your input so far.

Rob is right;

You should have your heating contractor produce the heat load from which he designed the plate-less staple-up radiant floor heating panel. We see a lot of staple-up or suspended tube PEX radiant floor here in Minneapolis, as it is common practice to leave out the aluminum heat transfer panels (almost always required in this climate). .

Taking the old, ugly cast iron radiator out of the new kitchen remodel and substituting radiant floor is a good idea (we do it all the time) but without a proper heat load it is " by guess, by golly" engineering and often as not, the results are disappointing.

We were just out on a consultation in Uptown this summer and of one of the licensed contractors with a 100 years of experience (not "combined") apparently didn't have enough, as the tube was bare, lacking plates or insulation! Needless to say the homeowner had a cold kitchen. The homeowner is now happy, having had the contractor back (on our advice) to install the aluminum panels required to satisfy the heat load for their new kitchen remodel.

As to where the heat went, the answer is often nowhere. We do not always install gauges (they cost money) but we always check supply and return temperature with our instruments. If the water comes back at the same temperature as it went in, no heat was transferred. Depending on flow having a close delta T is not unusual on a bare tube staple-up radiant floor heating system as it is an inefficient way to transfer heat.

No matter what kind of shiny goods you have under the tubing, it doesn't get the heat out of the tubing any faster. The emissivity of PEX is reasonably high, but you can get a heluva lot greater heat flux out of the PEX via conduction than you can via radiation. In a staple up the surface contact area between the PEX and wood is very modest, and in a suspended-tube you're counting on a combination of radiation + convective heat transfer (most of which will be radiation.) At higher tubing temps, you have bigger temperature differences, which in turn means higher heat transfer rates via radiation.

But when plated nearly 100" of the heat transfer is conduction between the tubing and plate (with much more surface contact than a staple up) then from the aluminum into the floor. The emissivity of aluminum is quite low- negligible in fact, and since the aluminum faces the joist cavity, the radiated heat flux downward is much reduced, rendering the reflective stuff pointless.

Plating it is SO much more effective at getting the heat out of the tubing and into the floor that you'd probably get more than adequate heating even if you backed off the temp a few 10s of degrees. If you retrofit some plates in there, snug up the insulation to the plates rather than re-installing the reflective layer with air gaps. The long air gap channels of warm air are too easily displaced by air infiltration, and unless you have well sealed rim joists and foundation sills you could losing a good chunk of heat to "thermal bypass" air currents. Snugging the batts up the floor to minimize the gap provides at least some resistance to air moving through the joist bay.

The absolute numbers of infra-red thermometers are not to be believed, or even the relative numbers unless the materials have identical emissivity. If the floor covering has a higher emissivity than that inherently presumed by the IR thermometer it could easily be reading 3-5F high, and if it's emissivity is a lot lower it can read even 10F or more lower. Comparing the IR thermometer's number against the room-air thermometer for the delta to come up with a BTU/ft number, keep in mind that the number has very large error bars around it. When you point it at the PEX going into the brass or bronze manifold the PEX temp reads a lot hotter than the brass or bronze. Spray paint them both (any color you like), and the detected temp differences will be small, now that the emissivity is identical.

Black hockey tape is a nice way to get a solid reading from any surface. I don't think a wood floor surface emissivity is usually very crazy for an IR thermometer though.

I KNEW that hockey tape had to serve SOME useful function! (Saves on having to scrape paint later! :-) )

Wood floors may vary a bit with the finish surface, but IR thermometers still aren't going to give you better than 2F accuracy in absolute temp even with the emissivity dead-on the designed in assumptions (unless you're willing to drop a lot o' shekels.) They're much better at relative readings. You might do better to measure the temp of an interior wall with the IR thermometer for the room temp reading to determine the delta rather than a wall-mounted air thermometer.