Radiant floor heat planning.

747mopar · Apr 16, 2019

I'm pulling the trigger on the radiant floor for the addition so with many here being familiar with the installation why not gather some thoughts.

I did some research using their formulas and I'm coming up with 576' of 1/2" pex spaced on 12" centers so I'm thinking 3 192' runs. Looks like the better price on Pex is to just buy 1000ft (I can always use the extra elsewhere).

Looks like the best pricing on foam is buying it in 24 sheet amounts, the floor will take 18 but for an extra $40 I get 6 extra sheets. I may double it up around the outside perimeter then fill the voids between the post with foam instead of concrete too further insulating the slab from the outside.

Concrete will be about $1,200 @ 6" thick and another $264 in 1/2" rebar on 24" centers. Total will be in the $2,500 range for the complete floor providing I can get competent help and not have to pay professionals... I honestly don't want to pour it myself! I think if I rent some power tools I can manage the pour with little help.

So what recommendations do you guys have, pex in the center of slab? Anything I'm missing?

Cary McCune · Apr 16, 2019

I did mine myself and it is the best heating you can get- hands down. I even made my manifolds. You will not be disappointed, every person that comes in the house comments how great it "Feels".

If I recall you want to limit your lengths to 200' max - based on your tubing size (1/2") -verify this. Do not skimp on tubing, I.E. keep your spacing at 12" and buy another roll if you run short. I ran out and regret not buying another roll as it is noticeable in that area. You also need to run 100% oxygen barrier tubing if its buried in concrete. Lots of other details, but its pretty simple.

91r/t · Apr 16, 2019

Yep I laid my dads down in his garage and did 4 runs of 1/2" tubing at less than 300' which is what they said in various different forums/companies that do the heat professionally. I ended up with 4 runs at about 250' and then came back to the manifold within that span. Used the square wire for the flooring instead of the roll of the chicken wire so it laid flat and was easier to strap the plastic tubing to every 12". It was a bit more, but man it was so much easier than fighting the wire that had been rolled up and then trying to keep it flat. We used an insulation for the floor called Insultarp. It was a 7 layer insulation tarp made of bubble wrap/foam/tarp laid down on the gravel before any tubing,wire, etc was laid down. Trying to remember anything else we did. Oh we stayed away from the area we were drilling for the lift by 2' all the way around to not end up drilling through the pex when anchoring the lift. I had the lift mapped out where we were putting it and poured 24" deep by 3' pads where it was going to be mounted, which was overkill, but didn't cost mush extra in retrospect. Also, I drew it up in CADD before we laid the lines, but that was overkill as well lol.

skicker · Apr 16, 2019

I plotted this out using 3/4" pex runs...I was able to get 2 runs with 293 linear feet in each run...
I used the 5x10 wire mesh sheets when I did my floor...according to the takeoff I had you would need 12 of them...I overlaid them on this plan and then deleted all but one back out for clarity...
I think it's set up pretty close to correct...Check it out and see how it works...
I added an extra run at 6" o/c at the garage door to cover the additional heat loss there...

747mopar · Apr 16, 2019

Cary McCune said:
I did mine myself and it is the best heating you can get- hands down. I even made my manifolds. You will not be disappointed, every person that comes in the house comments how great it "Feels".

If I recall you want to limit your lengths to 200' max - based on your tubing size (1/2") -verify this. Do not skimp on tubing, I.E. keep your spacing at 12" and buy another roll if you run short. I ran out and regret not buying another roll as it is noticeable in that area. You also need to run 100% oxygen barrier tubing if its buried in concrete. Lots of other details, but its pretty simple.

So far by my figures I need 576 foot of Pex, 1,000 of pex is only $200 so I won't be short lol. I'll buy the oxygen barrier line as well although Central Boiler said it's not necessary since the additive I have to run takes care of that but something that's getting burried in concrete is not a place to skimp!

Please post some pictures of your setup.

747mopar · Apr 16, 2019

skicker said:
I plotted this out using 3/4" pex runs...I was able to get 2 runs with 293 linear feet in each run...
I used the 5x10 wire mesh sheets when I did my floor...according to the takeoff I had you would need 12 of them...I overlaid them on this plan and then deleted all but one back out for clarity...
I think it's set up pretty close to correct...Check it out and see how it works...
I added an extra run at 6" o/c at the garage door to cover the additional heat loss there...

View attachment 751236

Wow, your termination point is really close haha. If the pink lines came straight out instead of looping back into the green you would have nailed it. Looks pretty simple. Explain the advantage and disadvantage of 3/4" vs 1/2", I read that they prefer a little turbulence as it transfers heat better but not so much flow that it wears on Components. Basically they are saying that the water should have a pretty brisk flow which is why I thought 1/2" would possibly be better?

skicker · Apr 16, 2019

I had involved a heating "Consultant" early on...That's where the 3/4" came into play...I'm not qualified to call out its advantages or disadvantages... In essence I took it as it has roughly 50% more volume which would have worked out in my mind to more heat...It also has more surface area to transmit heat from...You would want to know exactly where you plan to terminate and begin your connections as that will change the tubing length some...

I used the pre-bent PVC 90 degree elbows to run my penetrations thru the slab in a sleeve.

If your not planning on heating it all of the time you could maybe lessen the insulation below the slab as that is there to help hold heat in all of the time...If your going to do short heated times and not work out there all of the time there's not a lot of advantage to a lot of insulation under the slab.
I used the reflective Thermax product that was 1 1/2" thick under mine where it is slab on grade...

ws27 · Apr 16, 2019

If you are using a 1000' roll, put all of it in the slab...within reason. I'd recommend spacing at 6", but I don't know your dimensions. The length of the loops will determine the proper circ. Spend some time here: https://www.pexuniverse.com/how-size-circulator-pump. It even uses 1/2" pex for the example.

It won't hurt to add more tubing, advantage is more BTUs into the slab-quicker slab temp run up, disadvantage will be more cycling, but that won't matter to you.

Rebar should be at about 25%-33% of thickness for a downward load. I'd just put the tubing on top of the rebar.

It's not rocket science, you've done far more complicated things!

bm02tj · Apr 16, 2019

You are getting good info
Re Oxygen barrier tubing use it so you use less chemical
Yes 200 ft is max for 1/2 in try to keep all runs same length then you donot
need balance valves
90 degree pvc to protect tube is good
I like to go 6in on center for first two rows the 8in then 12
with 6in concrete you can stretch to 18 to 24 in center of shop
with extra at door with a thermal break so you donot heat the outside world
if you soil is extremely dry R5 under if not R10
Thermal break to outside walls
max temp into floor is 130F but try for less

Cary McCune · Apr 16, 2019

bm02tj said:
You are getting good info
Re Oxygen barrier tubing use it so you use less chemical
Yes 200 ft is max for 1/2 in try to keep all runs same length then you donot
need balance valves
90 degree pvc to protect tube is good
I like to go 6in on center for first two rows the 8in then 12
with 6in concrete you can stretch to 18 to 24 in center of shop
with extra at door with a thermal break so you donot heat the outside world
if you soil is extremely dry R5 under if not R10
Thermal break to outside walls
max temp into floor is 130F but try for less

Clarification regarding the 90 degree pvc note. I would use conduit sweeps to bring the tubing up rather than pvc.
Use hog wire, or similar and zip-ty all the tubing to it for spacing and to ensure the pex doesn't daylight.
FYI- I run our water temperature at 108 for the desired home temp but we have a very mild climate here.
My pump has been a taco pump, with a cartridge style guts one per zone, been working flawlessly for 9 years.

bm02tj · Apr 17, 2019

conduit sweeps are pvc
Pex and pvc need to be kept out of the sun for long life

747mopar · Apr 17, 2019

bm02tj said:
conduit sweeps are pvc
Pex and pvc need to be kept out of the sun for long life

I think he's meaning rigid galvanized pipe (industrial conduit) for better protection? If I use PVC I'll make a channel out of steel to protect it anyways so no issue there.

747mopar · Apr 17, 2019

As for the daylight issue, this addition is already under roof so very little light will be on it.

747mopar · Apr 17, 2019

skicker said:
I had involved a heating "Consultant" early on...That's where the 3/4" came into play...I'm not qualified to call out its advantages or disadvantages... In essence I took it as it has roughly 50% more volume which would have worked out in my mind to more heat...It also has more surface area to transmit heat from...You would want to know exactly where you plan to terminate and begin your connections as that will change the tubing length some...

I used the pre-bent PVC 90 degree elbows to run my penetrations thru the slab in a sleeve.

If your not planning on heating it all of the time you could maybe lessen the insulation below the slab as that is there to help hold heat in all of the time...If your going to do short heated times and not work out there all of the time there's not a lot of advantage to a lot of insulation under the slab.
I used the reflective Thermax product that was 1 1/2" thick under mine where it is slab on grade...

View attachment 751243 View attachment 751245

Here's the thing, until I see how much more wood it takes I have no idea how I'll use it. I'll likely start the heating season with the floor set at a comfy temperature and gauge the wood consumption, if I see little difference then I'm leaving it there, if it's going through wood then I'll only use it when needed and keep it just above freezing. Given that I'll insulate the crap out of it in hopes that it requires little to heat.

For insulation I'm planning on 2" thick rigid foam, since I'll have extra and this is basically a pole barn style building I'll fill in between the post with at least 6" of foam vertically and possibly even double up the foam 2' around the perimeter under the slab? Having it adjoining a heated garage on one side will surely be a plus as well on heating.

Still throwing it around in my head the best way to create a thermal break at the garage door??? I'd like to do foam there as well but it will have to have something capping it?

I'll research Pex dia some more, both arguments make sense. Bigger means more surface and volume but smaller means more flow, more flow might result in the water carrying it's heat for longer distances? Worth looking into further but the shop that sold me my boiler is heating 10,000 sq ft of buildings very efficiently with 1/2".

Cary McCune · Apr 17, 2019

Sorry for the confusion- Yes- use flexable(not metal) pvc conduit SWEEPS to stub out. This makes the 90deg transition and provides a protection sleeve for the pex.

mopar 3 B · Apr 17, 2019

For sheet mesh I would use 6x12-4/4 in the widest and longest sheet size you can haul. Supported on individual plastic sand supports at 2 ft. oc. each way. You do not want your PEX varying in depth and the 6x12 spacing will help with the PEX spacing. Every one in this region places the PEX 2 inches down from the top.

jason79 · Apr 19, 2019

I bought one of these years ago, best investment I ever made for radiant heat.

Just lay your 2in foam, staple the lines to it. Put your mesh or rebar over it. Done. Rent or find someone that has 1. Tying pex to rebar sucks! As for the heating, 1/2" pex is just fine. That is all I have ever used. 3 250ft runs would be ideal. Just make them even in length and put the warm end of the runs on the perimeter. PVC conduit 90s work great for terminating thru the concrete.

mopar 3 B · Apr 19, 2019

jason79 said:
I bought one of these years ago, best investment I ever made for radiant heat.View attachment 752762
Just lay your 2in foam, staple the lines to it. Put your mesh or rebar over it. Done. Rent or find someone that has 1. Tying pex to rebar sucks! As for the heating, 1/2" pex is just fine. That is all I have ever used. 3 250ft runs would be ideal. Just make them even in length and put the warm end of the runs on the perimeter. PVC conduit 90s work great for terminating thru the concrete.

You put foam over concrete or foam over rock?

bm02tj · Apr 19, 2019

If it was only 4in thick that would be good but 6in thick you will need out door reset or you will be over heating space as it will take to long for surface to respond

747mopar · Apr 20, 2019

jason79 said:
I bought one of these years ago, best investment I ever made for radiant heat.View attachment 752762
Just lay your 2in foam, staple the lines to it. Put your mesh or rebar over it. Done. Rent or find someone that has 1. Tying pex to rebar sucks! As for the heating, 1/2" pex is just fine. That is all I have ever used. 3 250ft runs would be ideal. Just make them even in length and put the warm end of the runs on the perimeter. PVC conduit 90s work great for terminating thru the concrete.

Looks like a handy tool but also looks like a bad idea as far as Pex placement? By placing the lines on the foam there will be limited surface contact with the concrete, I would think putting it in the center or closer to the surface would be ideal. I'm a glutton for punishment so fastening it down to wire won't bother me.

Thanks

Radiant floor heat planning.

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