Should I put staple-up radiant heat in my new house?

bphillips921

Long time lurker, first time poster.

I recently built a new home, moved in 5 months ago. I had 1/2" pex buried in my basement slab, garage slab, and basement garage slab. I have a little HVAC experience (did it in high school and college) and I like to DIY so I left the boiler and primary/secondary loop install for me to do. I'm now getting that installed and seriously considering adding a staple-up radiant system for my main floor (my basement is unfinished). I'm hoping you guys can give me some feedback. First the facts:

- I have a 199K BTU Combi condensing modulating boiler with outdoor reset. 120K BTU is available for heating.
- My garage is 1,800 sq ft with 2 18'x9' garage doors (R-19). Plus R-19 in the 2x6 walls and R-25 in the attic plus about 60 sq ft of windows (windsor double panes). I'm estimating about 40K BTU use for the garage
- My (walkout) basement slab is 1,906 sq ft with 1 8'x8' slider door and about 75sq ft of windows (windsor double pane). It has 2x6 walls with blown-in cellulose insulation. I'll also ad R-19 to the basement ceiling. I'm estimating about 40K BTU for this space as well
- My basement garage is 420 sq ft, one 8'x7' door (R-19) and 2x4 walls with batt insulation. No insulation on the ceiling, but it is pre-cast below the garage. I'm estimating about 18K BTU for this space.
- All in-slab pex was stapled down to 2" foam board. 1" foam board was put between the slab and the foundation wall.
- I'm not willing to buy a different or new boiler.
- I plan to run the in-slab water between 120-130 degrees. I don't want to mess with mixing valves, so the staple-up would need to run at the same temp.
- The main floor (1,906 sq ft) is 3/4" OSB then manufactured wood floor on the entire floor
- I have a total joist length of 1,052 ft. So, running two pex in each joist, I'd need 2,104 feet of pex.
- I live in central Iowa. Most winters we see low temps of 0 degrees(f) and high temps around 20. But, we get the occasional high near or below 0.

My main floor is currently fairly conformable with just the forced air heat. I just feel like I already have most of the big equipment for radiant installed so why not add it to the main floor while I can. If I can do it, and do it right, for a reasonable cost I think I'm interested in doing it.

So, my questions:
- I don't want to do it if it will be noisy. What should I make sure I do and don't do (or use and don't use) to make sure it's quiet?
- Can my current boiler handle the extra BTU load of the main floor?
- If you were doing this, what aluminum heat transfer plates and pex would you use? I'm not opposed to pex-al-pex, but I'd like to avoid it.

All opinions are welcome. I'm just at a crossroads on if I should do this, so I'm looking to hear from the experts.

GroundUp

No pricing is discussed here, please edit your post. With that said, running the staple-up and slabs the same temp will likely flywheel the slabs like crazy on warmer days. Your 1" perimeter insulation should have been at least 2", so you will have a lot of edge loss. There's no reason 120k shouldn't heat the entire area if it's properly sealed and insulated, your basement loss isn't likely to be anywhere near 40k. I always use a Pex-A or PE-RT for staple-up to avoid noise, and something like Thermo-Fin or Joist-Trak is the cat's meow as far as plates go.

Dave H_2

@bphillips921
The existing heat is a furnace?

Water temp designs for Staple-up radiant floors range anywhere from 100-180F depending upon what you want it do meaning be the sole heat source of the space or just floor warming (supplements the forced air furnace). Sounds like you only need it to be floor warming so the 120F should be ideal.

I do recommend performing a heatloss instead of assuming what the actual heatloss of a space is to get your numbers.

As stated before, 120-130 for a radiant slab is high, really high and it wont operate properly; one day it will be really warm in the space, the next cold. Underfloor radiant typically needs a higher temp since there is no mass like concrete being directly heated. Mixing valves should be in your future for your slab application.

The underfloor system can act as a supplement as long as you setup the controls properly. Several ways to combat it, two stage thermostat where the radiant floor is stage 1 and the furnace is stage two or using floor temp sensing stats to control the radiant.

Dave H.

hot_rod

Do a laid calc those upper rooms, it is possible that you may not need the furnace if the load can be covered with a transfer plate system

Good that you have wood floors, carpet is a tougher heat😗

Zman

I would use Joist-Trak for the upper floor and run it all at the same temp. You could set the garage as a non-priority load if the temp in the house is not keeping up. Do you care if the garage temp drops a little on the coldest day? I suspect your boiler will keep up, if you run an extra couple of conductors to your t-stats you can add the priority zoning down the road if needed.

bphillips921

Thanks for the feedback, everyone!

It seems the consensus is that the joist-trak is the best heat transfer plate. I have no doubt that it's the best and worth the money, but it's expensive and puts the cost of the project over my "worth it" threshold. It also seems that it would be best to use different water temps in the floor vs the concrete slabs. That adds complexity and again kind of chips away at the "worth it" threshold. I guess I'll always have a radiant floored basement and garage to hang out in if my main floor is too cold!

TAG

If this is a long term house -- you will regret not having the warm floors. The regret will be in direct proportions to length of winter.

On my most recent project I used the extruded plates as usual for the retrofit part of the projects -- the only difference was I followed advice here and used 3/8 tubing. It was much easier to install and is working very well.

The heavy plates with better transfer and lower water temp requirements allowed me to keep the single temp water and run the 4 manifolds and 30+ loops. This system: concrete slabs, warmboard subfloor and retrofit plates --- all running off of one secondary pump.

Derheatmeister

Have you considerd Viegas climate panel ? IMO it is easier to install and has a better transfer..

archibald tuttle

standard omega plates should be sufficient and far more cost effective. blueridgecompany.com is one of my favorites because they have 3/8" plates. I'm a big believer in 3/8". way easier to run. I use 100' runs with two separate loops running in each bay because i got a lot of 100' rolls a while back but I doubt even 200' would be that problematic, but obviously 1/2" omegas are widely available. vevor.com seems to have some of the most aggressive pricing but they seem to run hot and cold with customers, getting about a 50/50 on trustpilot so I'd start small with them if that is your choice and make sure you are satisfied before going in for larger orders.

you can get omegas in 2' and 4'. i've never worked with the 4'. maybe those with experience of both will chime in.

Caulk in the plates to improve contact is my understanding of best practice and what i've done. There is a purpose made thermally conductive sealant but it doesn't appear to actually be available at the moment, supply chain perhaps. Again, I defer to anyone who has done any side by sides with available materials relative to thermal conductivity and appropriateness coping with differential expansion (which could go to noise although i haven't had much noise issue. My standard is sid harvey silicone because its cheap and flexible.

I agree with the folks who encourage you not to forego under floor (esp. if you are going to finish the basement, otherwise you can add it when you feel like it and if you are running your slabs you'll have a bit of a warm floor to start with. what kind of foam did you use for insulation with your slabs? I assume although you announce target temp, that might be 'design temp', i.e. what you want when its as cold as it gets, and that you are actually running some kind of reset curve off outdoor temps?

brian

bphillips921

@archibald tuttle have you experienced much noise using the Omega style plates?

I used 2" foam board under the slabs.

My design temp would be 70 degrees for the basement and main floor and maybe 50 degrees for the main garage. The smaller (420 sq ft) garage I just want to keep above freezing. So it's design temp is more like 40.

My boiler has an outdoor reset. I assume that's what you mean by a reset curve off outdoor temps?

archibald tuttle

I was wondering what kind of foam? there is EPS (usually white), XPS (usually pink or blue) and Isocynate (usually fancy mustard yellow/brown). That doesn't really make much difference to temperature choices and you can't change it now.

design temp I was asking for coldest outdoor temps you are designed. the outdoor reset is keyed between indoor target, like 70 at which point you need no heat so your operating temp would be equal to your indoor temp and then if you set 120 or 130 for your design temp, or operating temp at coldest anticipated the boiler will set up a straight line slope to determine operating temperature.

noise is mostly noticeable from cold start. if you operate with constant circulation and variation of temperature to outdoors you have a steadier state. I have never run floor radiant with a thermostat. my instinctive engineering says keeping to 2 foot lengths and separating them so they don't butt or overlap helps reduce additive effects of expansion but I defer to here assembled masses. I caulked the plates to the subfloor with light beads as well looking to reduce movement and keep up contact.

there was this brief moment like a decade or so ago when the graphite miracle film was going to take over this duty. I was kind of watching to see if this happened and discussion kind of fell away. that was the quickest link to anything available I could find. I haven't worked with it and wonder what kind of adhesive would be practical for install or whether you could staple up the pex relatively straight and run firring strips either side to hold the film against the subfloor and formed close against the pex. or if i were a glutton for punishment you could make some strips of 1" xps insulation maybe 6" wide by 2' long and rout down the middle with a 1/2" deep with 1/2" core box bit and put the graphite on the surface and force that onto 3/8" pex on the subfloor, you might want strip of 1/4" flooring ply to hold as a backer for the foam. you don't need the foam as insulation, so you could also just use 3/4 ply but the foam routs easily and gives just that little during installation. (this is how i make my above floor systems although I've used industrial aluminum foils about 4 times as thick as kitchen foil but I suspect this would work with graphite as well.)

honestly, after all that blue sky, I suspect you would be fine with omega plates because there isn't a lot of movement with them changing slowly between 80 and 120 vs. cold start. but i am interested if anybody is going graphite these days.

bphillips921

archibald tuttle said:

I was wondering what kind of foam? there is EPS (usually white), XPS (usually pink or blue) and Isocynate (usually fancy mustard yellow/brown). That doesn't really make much difference to temperature choices and you can't change it now.

design temp I was asking for coldest outdoor temps you are designed. the outdoor reset is keyed between indoor target, like 70 at which point you need no heat so your operating temp would be equal to your indoor temp and then if you set 120 or 130 for your design temp, or operating temp at coldest anticipated the boiler will set up a straight line slope to determine operating temperature.

Oh gotcha. I'm designing for 0 degrees(f) as the coldest temp. Thanks for the explanation on the ODR. That helps me understand how to set it up. So, basically the ODR sees that it's 70 degrees outside and that's what I want my floor temp to be so it sends 70 degree water. And if it's 0 degrees outside and I told it that I need 120 degree water to stay at 70 degrees inside then it sends 120 degree water. Then it creates a linear formula for all the temps in between, correct? Any tips on how to find out what water temp I need in my slabs when it is 0 degrees out? I'm familiar with the BTU=(GPM*500)/DeltaT formula, but that's about it. I'm planning a 20 degree DeltaT in my slabs.

The insulation under the slab is XPS(blue). To be honest, I'm not thrilled with the insulating job they did, it could have been better. But they had it insulated, piped, and poured in a matter of two days. I stopped by to take pictures of the pipe as the cement truck was pulling up.

archibald tuttle

that garage job is sweet. honestly i mostly trial and error for design temp. start off in the 110 to 120 area. and then if you want to adjust garage vs. house basement vs. first floor you set the temp for the space that needs the hottest and then restrict flow a little in loops where you want cooler. at least that's my emperical way of going about it. in theory there are better more predictable over their range of operation flow restrictors than ball valves but in practice i usually use ball valves causes that cost effective.

i'm hoping some other folks who have floors operating will chime in about the noise factor. if you plan to finish your basement i think it is a great idea to go underfloor and as long as you use continuous circulation you aren't going to get the temperature swings that kindle noise but i'd like to have others validate that from their experience.

i imagine since it sounds like you are in already that your 1st floors are already finished so overfloor isn't a choice. I don't push that so much in living rooms and wood floor circumstances but if you can work the floor heights out to your satisfaction going overfloor in the bathroom and kitchen is often a good plan. you can pour thin set or lightweight concrete relative low thickness and the put thinset tiles or other typical wet area floor over it. you can even float the click floors although the felt or glued on resilient material doesn't help the transfer. but i have installs like that and it doesn't cost like the floor tracks-and or i've made my own floor tracks - opportunity cost.

hot_rod

bphillips921 said:

@archibald tuttle have you experienced much noise using the Omega style plates?

I used 2" foam board under the slabs.

My design temp would be 70 degrees for the basement and main floor and maybe 50 degrees for the main garage. The smaller (420 sq ft) garage I just want to keep above freezing. So it's design temp is more like 40.

My boiler has an outdoor reset. I assume that's what you mean by a reset curve off outdoor temps?

The noisy transfer plates, called "oil canning" had more to do with the thickness of the aluminum or metal.
The thin flashing thickness, ones were bad news, or bad noise. Limiting temperature swing could help some, but they could still ping or click.

The other issue is how tightly they grab the tube. It should be a snug press fit. If the tube moves in the aluminum, it is more of a squeaking noise from the EVOH barrier rubbing the metal. Rub two pieces of pex together to hear that type of noise.

While adhesive or transfer grease sounds doable, it is not such a fun job to install tube with any semi liquid product. Especially over head.

The extruded, tempered, T-3, aluminum transfer are the best option and worth the extra $$ for both noise and best heat transfer.

Boring

We did a retro 17 years ago, used 1/2" pex in the basement over existing cement and a covering of Gypcrete...it's wonderful!!! The ceilings were open so we used 3/8 pex in extruded aluminum transfer plates....Have never heard any noise...there may have been a slight "ticking" in one of the bed rooms...but I haven't heard that in years....Do it, you'll be very satisfied.....

Boring

TAG

I can hear my the original system when it first starts up -- mostly the high temp loops as the PEX slips inside the pipe insulation. It's big house and I have PEX going all over the place. Since it's ODR with constant circulation .... unless it gets warm and turns off .... only hear it the first day and it's only for 30 min or so.

I have some of the thin plates -- I never hear them ... but, they are not going through much change

archibald tuttle

@Boring just traking methods and results. did you put insulation over the old concrete floor before the pipes and gypcrete cover?

Boring

No insulation...tubing topped with wire mesh to keep tubing in place and I suppose to give the gypcrete something to bond to and support...