New construction

USAFretired

Good afternoon everyone, we are currently in the construction phase of a new wounded veteran retreat and we are installing in-floor radiant heat with 1/2" PEX and a 5" concrete slab. We have 2 inches of foam under the slab and 3 inches of foam in the footer. Couple of quick questions, are there areas of the house where we should not run tubing? With 1/2" PEX is 12 inches on center acceptable? Thank you in advance for any other advice!

Steamhead

@USAFretired , you've come to the right place. Where is this facility located?

USAFretired

We are in Eagle Nest, NM @8500ft elavation

USAFretired

Most of our construction is being done by volunteers.....we've done a ton of research but could use any expert advise!

EBEBRATT-Ed

This is probably an @hot_rod question radiant isn't my thing.

Thanks to you and all the volunteers for what your doing

GW

here’s a few thoughts

Half inch, I think 300ft is the general max. 12” c c seems fine but I guess the official heat loss dictates all that. I’m presuming the structure will be modern and very tight.If it’s commercial, perhaps you need fresh air. All things to consider

Were not to run Tube – – – it may take more effort to try to “miss” places like the bathtub, closets, cabinetry, etc. however I would like to know where the walls are as to try and nut run tube where a possible “floating tube” may get nailed by the framers.

I like to fill the tubing with water to keep it from floating. Sure you can fasten it a million times as well

I like to pressurize- it’s very rare that the concrete guys will puncture ( I don’t think it’s ever happened on my jobs), but it it does you kinda need to know and be prepared to fix it ASAP. Bring your rubber boots or whatever they’re called nowadays

This is getting a little picky, but when the concrete is flying it’s spraying and splattering. It’s nice to protect the tubing as you come up through the wet slab. this could be done with a number of ways, trash bag, painters tape, what have you

I don’t know what you mean by the phrase footer. 2 inch under the slab seems wonderful. Do you have any vertical insulation on the foundation walls? That’s usually 2 inch as well.

USAFretired

Yes.....the foundation footer is where we are putting the 3" foam.........(foundation walls)

motoguy128

Good practice is to split the system into multiple zones, especially bedrooms so you have some temp control for personal preference. Then if it’s a large building, I’d split large common areas by north and south sides as solar gain to overheat south areas and north areas remain cool on mild days.

Something to consider.

As mentioned, you can save some by not putting Heat under kitchen cabinets, vanities, closets or islands. Stay away from toilets as the heat can melt the wax rings.

IF you have a large hot water demand, which I suspect, go with a boiler and large indirect tank. MFG will help you size it.

Steamhead

As @GW says, you need to do a proper heat-loss calculation before you even start to design the system. This tell you how much heat you need to generate and deliver to the various rooms.

The usual procedure is to design for a certain indoor temperature, say 70°F, at a certain outdoor temperature. For Eagles Nest, NM, according to a Google search, the average low temperature is 2°F, and the record low is -47°F.

Some other factors come into play here. Of note is the diurnal temperature variation, where nights are often much colder than days. From Wikipedia:

"Eagle Nest has a humid continental climate (Köppen Dfb), bordering on a subalpine climate (Dfc), with very large day-night temperature variations, very warm days and chilly nights in summer, and extremely cold nights in winter. On average, 250 nights have minima below 32 °F (0 °C) and 40.3 nights fall below 0 °F (−17.8 °C), though maxima top freezing on all but 25.5 days. Eagle Nest holds numerous low temperature records for New Mexico, including the coldest temperatures ever recorded in the state during January, March, April, May, July, and November.[7]"

This means that the heating system will need to respond to substantially different heating loads over the course of a day. Since radiant floors have a significant amount of thermal mass, they can take a while to respond to changing outdoor temperatures. Given this, it may make sense to design the radiant floors for a certain base-line output, and use something else (such as cast-iron baseboard) to handle the daily load variations.

You would do well to get in touch with @hot_rod , he is one of the best in the radiant field.

USAFretired

We have the place split into 5 zones. Hopefully that'll work. I'm trying to figure out what areas other than exterior/interior wall base plates and toilets to avoid.

hot_rod

I would highly recommend a heat load calc before you tube. Most manufacturers, reps and wholesalers can help

How are you installing the tube? Tying to 6x6 mesh?

No need to worry about toilets there a a number of good non wax closet gaskets available

Tighter tube spacing allows lower supply temperature, 9” is another common spacing. The load calc and design spells it out

Only one chance to get the tube right👍🏻

USAFretired

We're tying the tubing to the rebar which will be on the top of the foam/vapor barrier/remesh. I hope that makes sense

hot_rod

What is the spacing of the rebar, you need to tie the tube about every 12" so you need a rebar grid 1 foot on center, that is a lot of bar for a residential pour?
6x6 mesh is most commonly used to give you more tie points and less $$

Paul Pollets

You may want to have one of the large radiant manufacturers do a design heat loss and CAD layout for you. Uponor has a design fee, but the work is essential, if you don't have the software or previous experience. https://www.uponorpro.com/technical-support/overview.aspx

USAFretired

@hot_rod .........We're doing the Remesh and rebar. I'll ask my concrete guy what that'll look like.

Paul Pollets

I'd also put the 6x6 welded wire mesh up on 2" chairs within a 5" slab. Better performance and emmisivity.

hot_rod

As @Paul Pollets mentioned, both the bar and mesh needs to be elevated up into the slab, continuous strip bar chairs are the best way to keep all the steel in the pour

JUGHNE

And as someone pointed out do not use bricks.....apparently a sin in pouring slabs.
I did use bricks for my rebar with mesh on top, tried to keep it pulled up during the 6" pour. I believe the tubing is lower than it should be but the floor is comfy anyway.
Very slow to heat though. I keep it set to one temp.
It is a sun room that overheats easily.

Visiting family think that a 74 degree room with heated slab is too hot. But most of them have heat pumps.....their loss.
So a lot of shorts and tank tops at Christmas time by the visitors.

GroundUp

JUGHNE said:

And as someone pointed out do not use bricks.....apparently a sin in pouring slabs.
I did use bricks for my rebar with mesh on top, tried to keep it pulled up during the 6" pour. I believe the tubing is lower than it should be but the floor is comfy anyway.
Very slow to heat though. I keep it set to one temp.
It is a sun room that overheats easily.

Visiting family think that a 74 degree room with heated slab is too hot. But most of them have heat pumps.....their loss.
So a lot of shorts and tank tops at Christmas time by the visitors.

I never understood the brick thing; what's wrong with adding native material to a pour? My shop is done with #4 bar in a 12" tied grid on top of broken bricks and kicks butt.

As for the 74 degree room though, that is too hot. Far too hot. Coming from a person with radiant. Lounging around requires 66-67 degree ambient temps for us, 69+ with radiant will make me sweat at idle

JUGHNE

Maybe the brick absorbs water then shrinks leaving a void???
But the brick would get soaked before the pour as the sand gets sprayed down.

This is a sun room with a lot of glass.
Also I grew up cold, ice and frost on the inside of the bedroom windows.
And we only had 1 dog for 4 brothers.

motoguy128

Bricks are fired clay. It has a much different density and tends to absorb water if not glazed. Some brick is very light and porous.They might also thermally expand and contract different than concrete, which is a mix of cement and aggregate, usually limestone. Built locally, sometimes river rick, which are very dense. Ground up brick mixed in probably would be OK.

BillyO

might be overthinking the properties of a brick guys, really?

Zman

@USAFretired
Just sent you a PM with contact info. I can help you out with this.

nibs

In our build, the walls were in place prior to the floor pour, so we brought the pex through the doorway, we only did the supply and return through the opening so the rooms have a cold threshhold, extending a loop throuth the opening would have been nice on a cold snowy barefoot morning.