under floor radiant

drhvac

I am putting underfloor radiant in a section of my house. I'm using Viega heavy duty transfer plates. After the piping is in, I want to spray foam. These rooms I'm heating are above a garage, and as you know, rooms above a garage are very drafty and cold, so this is why I want to spray foam. I am hearing different opinions on whether or not to leave a gap between the piping and spray foam, or just spray foaming right over the piping. What is the best way? I'm leaning towards leaving a 1" gap. The other question is if I do it that way, What is the best and easiest thing to use to create that gap? I'm thinking maybe the cardboard panning they use for panning out returns in hot air systems? Your opinion is appreciated.

Mark Eatherton

I've heard both ways...

I've always done it without any air gaps, but have heard that if you have an air gap, that it enhances the insulations R value.



Gap can be with or without aluminum.



I'm just guessing that an air gap might give you another .5 R value, which for the effort may or may not be worth it.



I've never had any complaints on those systems where I used FG insulation and held it tight to the face of the plate.



YMMV...



ME

Greg Maxwell

Air Gap

We have always recommended a 2" air gap between the plate and the insulation. It will minumize downward heat transfer.

Ravenwoods

Gap and reflective foil

I've always heard you should have a 2" gap with reflective foil to reflect the heat upwards.

Currently I'm removing my baseboard heating system and putting pex under the floor boards. I've got a bunch of used rigged insulation with the aluminum foil surfaces. I'm using 2"x2" to serve as spacers between the subfloor and the rigged foam insulation, which are actually 1.5"x1.5". About half of my rigged foam is 2" thick and says it is R14 and the other half is 1.5" thick and says it is just over R10. On the bottom of the floor joists I'll screw on sheets of osb and then blow in cellulose insulation from the side and dense pack it to prevent settling.

I've wondered about the recommended 2" gap and whether my smaller 1.5" gap will make much difference. Maybe there is some reason such as the wave length of radiated heat for this specific distance?

drhvac

sounds like a good idea

how you are going to do it. Using a 2x2, then attaching rigid foam. I'm not concerned about insulating because I just need something to create the space, then the spray foam I'm having done is really going to seal things up, and insulate it well. I could probably use your 2x2 method, then just attach card board to it, then the spray foam would go right up against the card board. What do you think? I am still hearing mixed opinions about leaving an air gap, or just spray foam right up against the pipe. I really wish somebody could convince me that just spray foaming without the gap would work just as well because creating the space for the gap is going to be alot of work. I looking at about 850 sq. ft., its going to be a mission. But if it will make the system work alot better, I don't mind doing it.                                  

Ravenwoods

From Dan Holohan's Book: Hydronic Radiant Heating

Here is what Dan Holohan's book says on page 108-109:



"With this type of installation, you also have to bounce the radiant energy off the tubing and up onto the bottom of the subfloor so the top of the finished floor heats evenly all the way across. You'll use foil face insulation to do this. It's important to have the foil facing upward toward the floor, and it's crucial that you leave several inches of airspace between the tubing and the foil. That's so the radiant waves of energy can diffuse down within the joist bay and bounce back up onto the underside of the floor. A lot of installers make the mistake of pushing the insulation tightly up against the tubing when they do their first job. This seems to make sense at first; they figure if the insulation is packed tightly , the heat won't leak out the bottom. But what actually happens is that the heat concentrates around the area where the tubes touch the floor. Upstairs, the customer can feel hot and cold spots on the topside of the floor. Had the installer left the air gap between the foil and the tubing, the radiant energy would have had a place to bounce around and smooth itself across the floor. "



Instead of cardboard, maybe use the rigid insulation like I am. You can buy 3/4" thick too.

Ravenwoods

Viega heavy duty transfer plates

I guess the transfer plates would be able to spread the heat out to the floor even if the insulation is pressed up against the tubes.



But I imagine the Viega heavy duty transfer plates are rather expensive. It would probably be much cheaper to use the reflective rigid foam insulation and more effective in evenly distributing the heat to the bottom of the subfloor.

drhvac

climate trak

I did use the climate trak panels, and they weren't cheap, but I think they will pay for themselves in time. It is a good quality plate that I am sure will transfer the heat well. I made a call to Viega today, and they said with spray foam I could spray right over the pipe and it will work well. Are you stapling your tubing up with out plates?

CMadatMe

Plateless in Radiantville

Suggest you find the post title article and read it before making a final decision. I'm using my I-pad and don't have it with me to post. Maybe Mark or someone else could post the article written by Siggy for you.



I'll leave you with this. The cost to fix a plateless system that doesn't work or performs substandard, costs significantly more then the cost of the extruded plates. Make sure your doing your homework with your heat loss, water temps and zoning.





Whe using extruded alum plates you insulate to the plate. There is no need to create a convection oven in the bay. You want to transfer the energy absorbed into the plate directly to the floor. Insulation is your friend.



I've been a part of fixing more plateless systems because of two reasons. I don't need the plates they cost too much and the dog ate my homework.

drhvac

I agree

Chris,

I definately agree with you about the plates. I have done alot of homework on this, and heard many nightmare stories when not using the plates.

drhvac

Now on to the boiler piping

I think I know the answer to this but would like a second opinion. I have 2 baseboard zones that I am tying this 5 circuit radiant zone in to, they are zoned with zone valves. I want to pipe this system using one pipe primary secondary. When I take my baseboard zones off of my primary loop, could I just pipe the return directly back to the return, instead of going back in to my primary loop using the spaced tees? Obviously the radiant zone I would use the spaced tees and pipe it back in to the primary loop.

My reason - On the coldest day when all zones are firing, if i piped the baseboard zones using the spaced tees, I would lose 10 degrees going to the radiant zones.

thx

STEVEusaPA

just a little confused....

Would help if you could post a sketch.  Did you do a complete heat loss/load workup before you started?. How did you size the length of the radiant zones?

 "Losing 10 degrees"?  Doesnt your radiant zones require a much lower water temperature?  How are you lowering the supply temp to the radiant? Mixing valve, injection, bypass? Just draw a sketch, and we'll help you tweak it (don't forget to list pipe sizes).

drhvac

load calc.

Hi Steve,

I did do a heat loss through the Viega radiant wizard. Total load for the radiant zone was about 15,200. water temp design on coldest day was 162 degrees. I'll work on a piping schematic for you. If I pipe the baseboaed zone using the closely spaced tees, my mixed water return temp would be 170 degrees going to my radiant zone, instead of 180. I know my load says 162 design temp, but having that extra 10 degrees would be a little extra if needed. The heat is going through carpet in some areas. i am using a viega manifold that has a pump, and mixing valve built in to it.

drhvac

load calc.

Hi Steve,

I did do a heat loss through the Viega radiant wizard. Total load for the radiant zone was about 15,200. water temp design on coldest day was 162 degrees. I'll work on a piping schematic for you. If I pipe the baseboaed zone using the closely spaced tees, my mixed water return temp would be 170 degrees going to my radiant zone, instead of 180. I know my load says 162 design temp, but having that extra 10 degrees would be a little extra if needed. The heat is going through carpet in some areas. i am using a viega manifold that has a pump, and mixing valve built in to it.

STEVEusaPA

hey can you also post

the heat load calc.  162 degree water for radiant seems too high.  Let's make sure the calc was done correctly, and you're using the right size pipe, & pumps.  The wallies may be able to come up with a different, better solution.

I would also like to know what was your final decision about insulating, especially over the garage.  You're comment about 'being drafty and cold' shouldn't apply anymore, once you insulated it properly.  Might help get that water temperature down.

drhvac

having hard time

getting the calculation out of the viega software, but I could tell you I have been doing load calcs for hvac systems for years, so I am familiar. I also had my distributor do a load calc for me, and they came up with similiar numbers. The thing is in most rooms, the heat has to go through subfloor, hardwood, and carpet, so this is why the temp is so high on the coldest day. As far as insulating I am going to spray foam tight to the floor and all around the perimeter, so I think this is going to help alot, compared to using just regular batt insulation. But you could see now why I want the ability to get higher water temp if needed. I have an outdoor reset connected to the system too I should mention. I didn't sit down and figure all my boiler piping sizes yet, but I'm thinking a 1 1/4 primary loop, with 1" going to my radiant zone, and 1" to my baseboard zones splitting to two 3/4 zones. I'll get you a piping layout as soon as I figure it out to see what you think. Do you have any pump curve charts for taco pumps? I have a 007 on there now taking care of baseboard zones.

NRT_Rob

with all due respect to dan

our belief is that upward facing radiant barriers in joist cavities are, long term, a waste of money.



I've seen some pulled down. they aren't very shiny anymore.

NRT_Rob

to second other posters

reflective insulation, even when it works, does not do what heavy plates will do.



it's not just about even floor temps. it's about average conductivity.

NRT_Rob

uh

if you have that much insulation above the plates, you better insulate the heck out of it downward.



I would consider scaling back to floor warming (no plates) with panel radiation in the room. Primarily because I am a strong advocate for low temperature design, not just for efficiency but to keep your heat source options in the future.



Maybe at least rough in some a couple of lines for future radiator retrofits, to cover yourself.

drhvac

piping diagram

This is how I was planning on piping this job. Please take a look, at let me know what you think. Its not a fancy computer drawing, just a rough drawing by hand, I'm old school. I know 162 is high for radiant, but remember this is worst case scenario on the coldest day. There are only a couple of rooms that have carpet. If it is a problem, I plan on taking the carpet up, a refinishing the hardwood floors that are already there. I probably going to do that anyway. I used alot of the climatrak plates underneath,, and by spray foaming its going to make it very tight. Thanks again for the help.

NRT_Rob

no mixing

I believe you're probably going to want to add mixing for the radiant.



If not, then you could probably just add it as a baseboard temperature zone valve takeoff unless you're right at the capabilities of that pump

STEVEusaPA

I agree with Rob about the mixing

Look at Tekmar's website for the essay on injection looping.  Has all the info you need, if you choose to go that way.  Also, on you're radiant loop, after you decide on mixing, you want circ on the supply, pumping away from the primary loop.  You probably know this, but if you're going with the ball valve between the closely spaced tees, make sure you have your secondary loops close together, i.e--tee, ball valve, tee.

drhvac

mixing valve

I am sorry, there is a mixing valve included with the manifold, but I forgot to draw it in the diagram. I will take a pic of the manifold and send it. Also, I have a Tekmar outdoor reset already connected to this system which will regulate the water temp. so that it is not running at 180 all of the time. I think I seen this thing fire at 180 degrees maybe once in the 3 years that I have it.

drhvac

manifold

Ok I attached a few pics, one being the manifold. Yes I do know about pumping away from the primary loop, but as you could see, this is the way the manifold comes with the circulator on the return going into the mixing valve. Any idea why they would do it this way?

drhvac

try again with pic

first attempt failed

drhvac

pic

last try

drhvac

stupid question

Thanks for all your help with my past questions on this radiant job I did in my own house. 1/2 the house is radiant, and the other is baseboard. The new radiant zone is very comfortable when it is running. The section that has radiant is very well insulated, I had it sprayfoamed. Its not really a problem, its actually a good problem, but what i am finding is that after the t-stat is satisfied, the floor stays warm, and the temperature may go up a degree or 2. Then the heat wont come on for a long time because the house is so tight. Floors cool off after a while, then that "cold 70" feeling comes back instead of the nice cozy "warm 70" when the floors are warm. I know the most efficient system is one that doesn't run, so I shouldn't complain, just would like that warm floor to stay warmer longer. Any idea's? thx

Gordy

Caveat

  Its one of the caveats of tight well insulated homes, and RFH. They either easily over shoot, or water temps are so low that the cozy warm floor does not exist. Constant circulation may help smooth out the peaks, and valleys a bit. Bottom line is that your room only needs so many btus to reach 70*. You may find as weather starts to get colder your warm floors may exist a little longer between calls.



 Thats one reason why I like ceiling radiant, with RFH in baths, and tiled areas as floor warming.



Gordy

Jean-David Beyer

I do not think that is a stupid question.

Then, again, I am not a heating professional.



I had a oil fired 60 year old boiler that heated my radiant slab. And I, too got massive overshoot and undershoot (if there is such a word). The problem with the old boiler, with no outdoor reset, is that it put hot water into the slab for 4 to 8 hours to warm up the house enough to satisfy the thermostat. But then the slab continued to heat the house for another 4 to 8 hours. Similarly on the way down.



I now have a mod-con with outdoor reset. I have the reset curve set very very close to the heat loss. So instead of putting 130F to 140F into the floor, I normally put in much less. Right now (50F outside), it was putting 75F water into the slab. The thermostat has called for heat for 8 hours and 13 minutes since midnight. The floor is lightly warm, but it could not be over 75F, because that is the temperature of the supply water. The system normally holds 69F +|- 1F all the time now.



I now never put 130F or more into the slab. The reset curve tops out at 120F when it is 6F outside, and design temperature around here is 14F.



Since my house is pretty well insulated, I do not get the "warm" floors that I used to get. In fact, they used to get too hot sometimes, and too cold other times. I do not expect warm floors unless it is very very cold outside and the supply to the slab goes up to 112F (say, on design day). I do use higher temperatures in my baseboard zone, but that is another story for another time.

NRT_Rob

not a lost cause.

this means the reset curve for this area is probably not set correctly... it's operating at too high of a water temp.



can solve if it has its own reset curve or if the curve is too high for everything else too

can help to install a floor sensor capable thermostat

better thermostat anticipation is also good.... PID logic stats.



but if the water temp is too high everything else is a bandaid.



it's true that "hot floors' won't be prevalent in low loads but conditioned floors are always more comfortable than unconditioned (off and cooled down) floors.

drhvac

outdoor reset

I have a Viega manifold set up with this system that has a mixing valve built in to it. The mixing valve can be manually set up by setting a maximum temperature you want the radiant to see. If you did it this way which is the way I have it set up, you set it on what ever your load calculation says what temp the water should be on the coldest day. My boiler is hooked to an outdoor reset. The coldest it has been here has been in the 30's, and I haven't seen the water temp go above 140. However, 140 is to high for the radiant, so I think the floor is getting to hot to quick, and causing the t-stat to overshoot. my floor temp has been around 78 - 80 when the heat has been on awhile. This mixing valve that is hooked to the viega manifold has the option of hooking a seperate outdoor reset to it so that it modulates based on the out door temp. I think if install this, I will have lower floor temp, and longer run times which will make the system more efficient and comfortable ?

NRT_Rob

yes

install the sensor.

CMadatMe

Indoor Feedback

If that station is similar to the link this make be the anwser.



http://www.hydronicalternatives.com/EM-32_Installation_instructions-2010-04-01.pdf