Radiant heat/boiler/foam recommendations

[nemise]

I know there's a ton of posts here about radiant flooring, I just haven't been able to find the answers to a few questions I am wondering about.

I am doing a 2 car garage with living space above. It's 26x32, attached to my existing home. I want to do radiant heat in the floors for both levels. Even if I don't use it in the garage very often, the extra cost really isn't that much to put the pex in the slab, so I figure why not.

So for the garage level, after the foundation walls are poured and waterproofed, am I right in thinking that I should put 2" XPS fiber boards on the inside of the foundation walls, all the way from the footings up? How high up? Below the slab, or on top of the slab? If it's above the slab, that means the slab wouldn't touch the walls. Is that right? It doesn't seem right to me, and I haven't been able to find that answer. Should it go all the way down to the footings? That means I have to do it before backfilling. What PSI for the walls? Best place to get it?

For the slab, what do I do? Put down crushed stone, then 6 mil plastic vapor barrier, then insulation, then wire mesh, then tubing, then pex, then pour? What PSI for the floors? Where do I find it?

This will be attached to the house, but I will not be heating the garage all the time, so should I insulate the wall between the house and the garage? what about the ceiling? Insulate the garage from the 2nd floor living space, correct? I plan on using closed cell foam.

On the 2nd floor I plan on clipping the 1/2" pex to the plywood subfloor and using gypcreet. How much space do I leave for door frames? I'm assuming the closed cell foam on the ceiling of the garage is my insulation here to keep the heat up, correct?

What about the roof rafters? In the existing house there was fiberglass on the roof rafters. The building inspector said to take it down, so we did. I get different answers about whether or not I should spray open cell foam on the roof rafters of the existing home and the addition when I do it. Or should I just insulate the ceiling of the 2nd floor? Not too worried about the cost of the foam. I'd rather just do it right the first time and not pay crazy heating/cooling costs.

I have solar on my home, and I generate about an extra 1500-2000kwH / year over what we use right now. Our current heating system is natural gas forced hot air. Would I be best sticking with natural gas and getting a tankless water heater to power the radiant floors, or should I go with something electric? I am in the Northeast (MA).

Is there anything I'm missing here? This is my first addition and I am subbing it out myself as the homeowner, so I'm just trying to think of everything ahead of time and get it right the first time to avoid additional costs.

Thank You!

 

[anthony666]

sounds like you have the perfect set up to use spray foam insulation for both the slab and the underside of your floor .. the purple stuff, i believe it's 2 pound ?? cmiiw

compact your gravel, blow the foam over the floor, up the walls and over the underside of the joist cavity in one big seamless envelope

if you use xps; compact gravel, vapor barrier running up the walls a few inches higher than finished height of slab, tuck taped xps, a thermal break around the perimeter, wire mesh 1/2" he-pex and pour

i'd spray the **** out of the 2nd floor as well

gypcrete does expand slightly, but not enough to bind the doors

most hvac supply companies will rent you a stapler to staple down the pex, it allows you to pour a little less gypcrete and still get enough coverage to prevent cracking than those big clunky plastic pex clips, which also get expensive .. i made my own from a 15/16ths roofing stapler i got used from ebay for 20 bucks, i made a plate that spaces the stapler off the floor just enough and also act as a guide so i don't fire staples through the pex .. the ones sold specifically for the job cost a couple of grand !!

 

[nemise]

So you'd recommend using the BASF Walltite ECO over the XPS foam board? Can you weigh in on where exactly this gets sprayed on the sides? all the way down to the footings? How far up? Just below where the slab is going to start, or should it go up past the slab? Would you actually see the foam on the inside of the concrete inside the garage? This is where my confusion is, how far to come up with the insulation from the footings.

 

[jvitez]

For a heated living space over an unheated garage, the only way to go is high density closed cell spray foam, also called 2 lb foam. Closed cell means the foam itself acts as an air/vapour barrier, so not only does it provide about R7 per inch, but it completes seals the floor, so no air currents and thereby no conductive heat loss into an unheated garage.

We used exactly this type of foam in the above grade walls of our home. We used R24 fibreglass batts in the basement, and I now kick myself for not using spray foam there also.

 

[yeldogt]

anthony666. I have never done the spray foam under the slab ... can you explain it a bit more for the OP .. and me

It is not done around me .. although people say they have seen it? My inspector is having issues. I have used the spay foam in a trench with insulated Pex for heat betweens buildings.

My inspector is concerned about the vapor barrier and insects!

 

[nemise]

@jvitez, is there more than open and closed cell spray foam, or is it really just those 2 and the rest is just the brand name, but otherwise they are the same. Such as icynene, basf walltite eco, etc.

 

[anthony666]

My inspector is concerned about the vapor barrier and insects!

the 2lb stuff, AFIK, is it's own vapor barrier .. once it sets up its like a rock, you could tap dance on it without hurting it .. it conforms to the exact contours of the gravel, so no worries about stepping on xps over a high spot and cracking/breaking it .. no taping needed, no chance of drafts or water sneaking in, no worries about the thermal break on the edge of the slab .. the entire thing is sealed up tight as a drum

its not tubing season here right now .. when that stuff starts again in spring i'll make a picture or two

i dunno about bugs and rodents, but i can't imagine it's delicious or nutritious .. ill ask next time i see the installer

op .. is your garage framed construction or concrete walls to the ceiling ?? if you're worried esthetics cover it with peg board or drywall or that awesome fake wood panel stuff my folks had in their basement

 

[jvitez]

@jvitez, is there more than open and closed cell spray foam, or is it really just those 2 and the rest is just the brand name, but otherwise they are the same. Such as icynene, basf walltite eco, etc.

Pretty much that's it. Open cell is also called 0.5 lb foam. It's OK, but it doesn't air seal so you still need a vapour barrier in addition to the foam, plus it's not as physically sturdy as closed cell foam. Closed cell is also higher R-value per inch. Personally, I wouldn't bother with open cell foam. It negates the two most valuable properties of using foam in the first place.

 

[nemise]

There will be about 2 feet of cement wall visible at the bottom of the garage. Then the wood framing will start. So where exactly would I foam? On top of the gravel (under the slab) and on the inside walls of the foundation starting where and ending where? It just seems weird to me to do the entire wall because then the slab will never touch the foundation walls - isn't it supposed to? Aesthetics, I'm not too worried about. I can figure out something if that's the best way to do it.

 

[nemise]

When is open cell used? Roof rafters? Is it a good idea to insulate the roof rafters?

 

[jvitez]

When is open cell used? Roof rafters? Is it a good idea to insulate the roof rafters?

It all depends what you want to do with the attic space. If you want storage in the attic with heated/cooled air, you spray the roof underside with high density spray foam to have an air tight seal plus insulation. Mostly I've seen this done in the southern US when heat rejection from a hot roof if the more important feature.

Here in the cold Canuck prairies we build houses with ventilated attic spaces.

 

[anthony666]

There will be about 2 feet of cement wall visible at the bottom of the garage. Then the wood framing will start. So where exactly would I foam? On top of the gravel (under the slab) and on the inside walls of the foundation starting where and ending where? It just seems weird to me to do the entire wall because then the slab will never touch the foundation walls - isn't it supposed to? Aesthetics, I'm not too worried about. I can figure out something if that's the best way to do it.

the slab floats, don't worry it won't go anywhere .. the edges of the slab get insulated from the walls so that the walls don't wick the heat out of your slab

if you don't care how it looks blow the entire thing in except for the windows and doors obviously .. seal it up tight

 

[nemise]

Okay, thanks. So basically just make a big foam box around the entire garage, starting underneath the slab and continuing all the way to the ceiling. Works for me!

 

[anthony666]

Okay, thanks. So basically just make a big foam box around the entire garage, starting underneath the slab and continuing all the way to the ceiling. Works for me!

yep, exactly

 

[nemise]

@anthony666 - thanks for the info. Can you weigh in on what you think about an electric vs gas water heater/boiler with the info I posted in my original post about having solar?

Thanks

 

[anthony666]

@anthony666 - thanks for the info. Can you weigh in on what you think about an electric vs gas water heater/boiler with the info I posted in my original post about having solar?

Thanks

that's something you'd have to work out for yourself nemise, i know that up here in ontario if you are putting back into the grid more than you take out they pay you for that power, i dunno if that's the case there or the excess is just wasted .. you'd have to do the math and figure out how many btu's you need, how much those btu's will cost for both gas and electric setups, whether you produce enough power etc etc .. it'd be a shame if an electric boiler put you back into grid slavery .. i'd say you are one of the best candidates for an electric boiler i have heard of yet

that said, i'm a gas boiler man from way back .. electricity costs here are insane and electric boilers big breakers and often a panel upgrade

make sure you get a unit that is specifically designated suitable for space heating .. 'water heaters' as a general rule are not designed for long term steady use, or deal with air elimination

 

[nemise]

Here, when you generate more kwH than you use, those kwH credits get added to your account each month. Credits roll over month to month and do not expire. You can even give credits to someone else's account if you'd like. Over the course of a year I will generate about 2000 kwH more than I use.

How would I go about figuring out how many btu's I'd need for the heating months? I'm assuming I'd be able to look at previous gas bills and figure out something from there?

 

[anthony666]

no man, i don't think your old gas bills would help in this case, you're talking about just heating the garage and the living space above hydronicly, yea ?? the gas bill would give you an idea of the btu requirement for the entire house as it sat pre the build

check out donpowers' post #2 in this thread http://www.garagejournal.com/forum/showthread.php?t=272511

he gives the formula & how to use it