Can any one offer some insight into the "average" water temp for a radiant heat system? I have a new ICF home,spray foamed roof trusses, and green roofs w/ add'n. insulation and a membrane completing the envelope. I am heating  approx. 2000 sq.ft with 1-1/2" concrete overpour on 3 levels and heated with a 20KW Thermolec electric boiler w/ outdoor thermostat. The house stays comfortable, and rarely fluctuates more than a degree or two, but we don't really experience the comforts of radiant heat as the floors never seem to be "warm enough" (acid stained concrete, great passive solar, etc) We've had an increadibly mild winter, with only a few weeks of -25 weather, and my electrical bill has been very steep (don't have the PV system installed yet)  Anyways, back to my question: what temp should the water in my floors be at? Everytime I've checked, regardless of the outside temp., it has been between 32-39 C. I haven't tried disconnecting the outside thermostat and setting the aquastat to MAX., but I am thinking that if I pump more heat into the concrete, it should radiate better and hopefully utilize it's thermal mass, thus lowering my demands on the boiler. I understand that the modulating boiler will be working harder, but also would expect it to be running less. Any ideas? Perhaps my expectations are unrealistic, it just seems to be running too often and not getting the water as hot as I think it should be. We've checked it's draw while running, and it is correct, so I've ruled out any blown coils, etc.
Any help would be appreciated.

floor temp is a function of heat load. You are describing a very low heat load home... that means low surface temperature floors. You want the boiler to run 100% of the time at exactly the output you need.

to raise floor temps you'd have to reduce floor coverage area (turn off loops). it is possible to design systems like that with 'spot warmth' in high traffic areas, but typically low water temps are a bigger draw. For example you could use a heat pump (more cost effective than PV) and your low water temp requirement would result in excellent efficiencies.

Thanks Rob,

Just to clarify, I am better off with my boiler running more often, or always, at a low water temp?? I am hoping that when you say "low water temps are a bigger draw" that you mean that low water temps are more desireable AND NOT lower water temps are a bigger draw re: electricity.
I guess to prioritize, I am more concerned with energy efficiency than the comfort of warm floors (that's my wife's battle...) It makes perfect sense to me, once reading your advice, to live with my lower water temperatures as they are as hot as the home requires. I won't be using a heat pump, as the PV system is already paid for and just waiting to be installed. I don't have natural gas as it wasn't worth it to install ($5000 just to get iti to the house, min. $30/month regardless of use), so the PV panels will be supplementing the boiler and DHW (electric Rheem Marathon) and hopefully some of the the homes daily electrical requirements.Eventually we will have two 3KW systems on the property, but just one for now. Without the PV, I would never recommend an electric boiler as, even in this type of home, the 20KW boiler uses way too much electricity. Thanks for your prompt advice.

sorry, you are correct, typically low water temps are "more desireable".. heh..

you might want to consider a heat pump ... ad alert, we sell Daikin Althermas... even with PV. but you'll be able to judge where your total usage is after you put the PV up and decide how important reduction is at that point. point of fact though you could most likely cut your usage by 50-66% with such a unit (for space heat usage). depends on your real final heat load though.

What Rob said. In other words you don't need any more heat in the house. If you raise the floor temp, you raise the air temp. Are you comfortable with a higher room temp? Probably won't keep the floor warm for long anyway 'cause the room will eventually hit target and then slow down the heat to the floor. This is an issue we see more of all the time. If you build a code minimum house you have enough heat loss that the floor has to stay warmer to maintain the air temp. But 'cause you built top of the line, you don't need much heat therefore there is no need for the boiler to run hot.

I'm guessing you are north of the 49th. Weather conditions describe Alberta but with electric boiler, guessing Manitoba. If we still get a prolonged cold spell (like last year) your floor will feel warmer, but with ICF it will have to be at least 3 or 4 days long.

I'm in Regina Beach, Sk. Most messed up weather north of the 49th I'm sure...It was -33 (-45 w/ windchill) only 10 days ago, and was +9 two days ago...It is nothing to see a temp. swing of 40 degrees in 24 hours. Thanks for confirming, both of you, great advice, and I will look into the heat pumps.
I guess I will continue to let it run at will...I haven't timed it but I would guess that it kicks in every 2 hours for about 10-15 minutes...I hear it more than I should because I ran my 1" PEX supply and return lines inside an ABS conduit to the top floor (20' above boiler) and they knock every once and awhile as the PEX isn't clipped down inside the 8' length of abs (rookie mistake). Final question while I have your attention: the system is set up with 3 manifolds (walkout basemen/garage, main, and 2nd) and 2 thermostats (basement and main floor). However, I am not utilizing the zoned system and running everything as one system off of one thermostat and all of my relays in the open position vs. auto position. No issues with comfort at all, its just that when the main calls for heat, the basement/garage is obviously getting it too. Any problem with this other than the obvious lack of control? No room in the home is warmer or cooler than another with the exception of the garage which could likely be attributed to the 18' OHGD's opening/closing 4 times a day and/or because it's an insulated slab on grade vs truss system w/ overpour for the remainder of the walkout level.

Posted By dmcdfrom83 on 01 Feb 2012 02:43 PM
I'm in Regina Beach, Sk. Most messed up weather north of the 49th I'm sure...It was -33 (-45 w/ windchill) only 10 days ago, and was +9 two days ago...It is nothing to see a temp. swing of 40 degrees in 24 hours. Thanks for confirming, both of you, great advice, and I will look into the heat pumps.
I guess I will continue to let it run at will...I haven't timed it but I would guess that it kicks in every 2 hours for about 10-15 minutes...I hear it more than I should because I ran my 1" PEX supply and return lines inside an ABS conduit to the top floor (20' above boiler) and they knock every once and awhile as the PEX isn't clipped down inside the 8' length of abs (rookie mistake). Final question while I have your attention: the system is set up with 3 manifolds (walkout basemen/garage, main, and 2nd) and 2 thermostats (basement and main floor). However, I am not utilizing the zoned system and running everything as one system off of one thermostat and all of my relays in the open position vs. auto position. No issues with comfort at all, its just that when the main calls for heat, the basement/garage is obviously getting it too. Any problem with this other than the obvious lack of control? No room in the home is warmer or cooler than another with the exception of the garage which could likely be attributed to the 18' OHGD's opening/closing 4 times a day and/or because it's an insulated slab on grade vs truss system w/ overpour for the remainder of the walkout level.

Its typical for icf homes with floor mass to stay close to the same temp throughout so there is not as much benefit in zoning from that point. Two things that might make a difference. If you set the upper floor somewhat lower then most of the heat will be generated on the the main floor which might make the main floor feel a bit warmer. Not sure it will have much impact on the heating bill. Isolating the garage and running it at a lower temp might have a bigger impact on the bill. Lower delta t on each side of the garage door should show some saving.
Bob

zoning is about room by room heat loads.... they definitely can need zoning if the window distribution is uneven.

zone as required to maintain the temps you want in each space. if that is already happening, go with it.

You mention your electric bill being high. I have a very similar house to yours, complete ICF, acid stained concrete floor, passive solar, around 2400 sq ft, in Eastern Canada, with electric boiler. My total electric bill for December was $260 (~10 cents/KWH). This lines up closely with the software I used to estimate costs.

I would look into the air to water heat pump recommended by NRTRob as you could install the heat pump instead of more PV panels.