Hey guys I'm installing a radiant floor using Blue Ridges system. Most of my first floor is over a crawl space that we had encapsulated and sealed. I put fiberglass bats in between the joists before putting the subfloor on in that area, but what about over the basement. The basement is typical of one build 130 years ago, it's mainly a place for the mechanical aspects of the home but is accessed indoors. It sits underneath the kitchen. Since the big Veissman boiler is in there, should I just skip the insulation? Thanks!

Normally, you want way more R-value material below the PEX than above the PEX so most of the hydronic heat goes upward into the space you are desiring heat instead of downward. However, if you want to also heat the basement to some extent, you could determine the right amount of R-value insulation to put in the floor above the basement to accomplish this. Otherwise, just insulate it like you are doing with the other floor. I would suggest working with Dan at Blue Ridge to sort this out for you. He occasionally posts here, but contacting him directly would probably be your best bet.

I really don't need to heat the basement anymore than the boiler already heats it up. The thing is a monster. I don't understand what you mean by putting R value insulation in to heat the basement? If I put insulation in, it would be between the joints which would keep the heat in the pipes going up (they sit on top of the subfloor) and the heat from the boiler itself down in the basement correct? My thought that if I didn't insulate then the heat from the boiler would rise up as well along with the pipe heat..

If you don’t need to heat the basement, then fully insulate the floor above the basement. That way, most of the PEX hydronic heat goes upward into the space you are desiring heat instead of downward into the basement. You should have accomplished a room-by-room heat loss analysis and the hydronic circuits in each room should have been designed to provide this heat to each room using the design supply temperatures and flow rates.

The PEX hydronic heat moves upward or downward in direct proportion to the amount of R-value above and below the PEX. For example, if half the R-value is above the PEX and half is below the PEX, 50% of the PEX hydronic heat moves upward and 50% moves downward. Normally, you design a hydronic emitter so 90-95% of the PEX hydronic heat moves upward. You accomplish this by knowing what the R-value of the material above the PEX will be and then placing insulation below the PEX that has a R-value of 90-95% of the total hydronic emitter R-value.

Just because something isn’t sold as insulation, doesn’t mean that it doesn’t have R-value like insulation. Wood, carpet, tile and concrete all have R-value to varying degrees. Wood and carpet have a higher R-value than tile and concrete...hence wood and carpet behave more like an insulator than tile and concrete. This is why the performance of an under-floor hydronic emitter is worse than the performance of above-floor and concrete slab emitters. This is also why under-floor hydronic emitters are more expensive than concrete slab emitters. You need aluminum plates and lots of below PEX insulation in order to drive the PEX hydronic heat upward.

Unless your boiler is generating a higher air temperature at the basement ceiling than the temperature of the hydronic fluid in the PEX circuits in the floor above the basement, you should fully insulate the floor above the basement. Again, you should work with the company that sold you your system to answer these sort of questions and to meet all your needs.

If your boiler is heating the basement, air sealing and insulating the basement WALLS will save more money and heat than insulating under the radiant tubing (though you still want to have at least R-11 between the tubing and the basement for better zone control. If there is R13 under the the radiant floor section and the basement isn't frigid, it's enough, and raising that to R30 or something will barely move the needle. Money for insulating under the floor in non-radiant portions is better applied to air sealing and insulating the foundation and foundation sill, band joists, etc.

Even a passively heated basement is a conditioned space, and the heat loss out of the foundation can be a sizable fraction of the total heat load of the house. Sealing and insulating the foundation will raise the temperature in the basement, but lower the fuel use (sometimes by a lot, especially basements with air-leaky stone foundations.)

What type of foundation, and what's resting on them (big beams, sawn planks, something else)?

Got a ZIP code? (Local climate makes a difference on what makes sense for foundation insulation, in terms of both methodology and total R.

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Dana1, the foundation is brick and in the basement it has a thick stucco layer on it (water sealing maybe?) The crawlspace is encapsulated with a 20mil liner. There are 130 year old pine beams resting on the foundation. I'm in Indiana with a zip of 46062

lol, in my opinion, my crappy basement is the most comfortable room in the entire house year round- stays about 71

Posted By thesouth18 on 05 Jan 2018 10:38 PM
Dana1, the foundation is brick and in the basement it has a thick stucco layer on it (water sealing maybe?) The crawlspace is encapsulated with a 20mil liner. There are 130 year old pine beams resting on the foundation. I'm in Indiana with a zip of 46062

lol, in my opinion, my crappy basement is the most comfortable room in the entire house year round- stays about 71

You are in US climate zone 5 in a location with a bit more than 5500 annual heating degree days. Your foundation has a U-factor no lower U0.35 BTU/hr per degree F per square foot of area, it could be over U0.5 depending on the thickness and density of the brick. Assuming U0.35, when it's 30F outside, 70F inside every 100 square feet of above grade exposure foundation is emitting:

U0.35 x 100' x (70-30F)= 1400 BTU/hr

When it's 0F outside (roughly your 99% outside design temp every 100 square feet of above grade exposure is emitting at least:

U0.35 x 100' x 70F= 2540 BTU/hr

And that's just above-grade. Below grade the losses are significant too, but don't vary as rapidly with outdoor temperature.

If you have a perimeter of 100' and 1.5' of above grade exposure you're paying quite a bit for that 71F comfort in the boiler room- it's probably a significant double-digit percentage of your fuel bill, which could be brought to low single digit percentage fraction by insulating the basement (and crawlspace) to the IRC code minimum of R15-continuous insulation. With R15 on the wall the U-factor drops to under U0.05 and the heat loss of 100 square feet of above-grade exposure drops to less than:

U0.05 x 100' x 70F= 350 BTU/hr.

When you do that the temperature in the basement will rise a few degrees, but the lower heat loss overall reduces the duty cycle on the boiler too- you won't roast.

Dana1, thanks for the great reply. As of now I have been insulating the floor in between the joists. I have R38 over the crawl and R19 over the basement because those joist bays were filled with pipes, duct work, etc. Would it be any benefit to insulate the crawl and basement on top of what I've already done. I have access to about 3/4 of the crawl space so if I should, do you recommend rigid foam? If so as far as application, can I just glue it to the vapor barrier or does it need to be tapped in with screws and fender washers into the foundation?

Thanks!

Dana1, just to clarify, when I say the boiler is heating the basement, I just mean it heats it passively because the boiler itself gets hot, not because I'm actively trying to heat the basement. As a matter of fact, it's 71 degrees in the basement right now and I don't even have the boiler running. I don't have the system up yet, I'm running on an electric heat pump at the moment.

I get that it's just passive heating, by the MASSIVE standby and distribution losses of the boiler (and other appliances in the basement), but it's still heat that you've paid for leaving the house (instead of keeping the upstairs warm.)

Insulating between the joists in the basement (other than radiant floor sections) is a waste of money, since it isolates the boiler and it's standby/distribution losses from the fully conditioned space. If the crawlspace is vented and isolated from the basement, leave the R38 in place. It might have been easier & better to make it a sealed-insulated crawlspace, but as long as the joist edges or subfloor above the R38s don't grow mold (inspect it every now and then for the first handful of years) you can leave it as-is. Vented crawlspaces under air-conditioned rooms in your location can sometimes end up with high moisture content in the subfloor during the cooling season.

Dana1. I have the crawlspace encapsulated and the vents sealed. I run a very heavy duty dehumidifer which keeps it quite dry down there. I already have the floor insulated below the radiate, so would I get any additional from doing the basement walls and the crawlspace walls that I can get to. Sorry to be a pain.

If there are no heat sources in the basement, how is it that it's 71F degrees down there in the middle of winter?

Is the crawlspace also 71F?

Yes, there is additional benefit to insulating the walls of a 71F basement. That heat is coming from somewhere, and you are paying for it. (Unless it's coming from the buried nuclear waste under the slab... :-) ) Not so much from insulating a 40F (in winter) crawlspace, unless it's open to the basement and air moves freely between them.

The crawl is open to the basement. I honestly don't know what the heat source is but I'll get to insulating everything. Is glueing foam board to the vapor barrier ok? And you recommend R15 correct? I know they make a R10 foam board so I could glue a R10 and a R5 together.

Use 1x furring over the foam board through-screwed the foundation with masonry screws. Unless the crawl space it actually 70F it's probably not going to be worth going for the full R15.

Used 1.5" foil-faced polyiso foam (R9-R10), or 2" reclaimed fiber faced roofing polyiso (R11-ish for 2lb roofing polyiso) then cut 3/4" fire-rated Down Thermax (R5-ish) to fit between the furring you would then NOT have to cover it with a rated thermal barrier against ignition (such as half-inch wallboard.) You can use foam board construction adhesive to secure the 3/4" layer to whatever is up against the vapor barrier/foundation. Even with 1.5" generic foam + 3/4" Thermax would be R14-R15 where it's just foam, and R11+ at the furring, which should be good enough. With 2" roofing iso + 3/4" Thermax it would be over R16 between the furring, and R12-R13 at the furring itself.

Tape the seams of fiber faced foam with housewrap tape, tape the seams of foil-faced foam with 1.5-2" wide foil duct tape with a temperature rated adhesive (not some decorator foil tape.) eg: Nashua 324A is available at most box stores. Use can-foam or a bead of polyurethane caulk to seal the top & bottom of the rigid board, preventing convection around the insualtion layer. It's fine to cut'n'cobble the foam board up and over the top of the foundation, foundation sill, and band joist securing it with just foam board construction adhesive, sealing the edges & seams with can-foam or caulk.

With 2" foam and 1x furring it takes a minimum length 3.5" Tapcons to get a 3/4" bite into the masonry. If the brick is a softer type go with 4" screws. Don't sweat the annular ring hole in the vapor barrier around the screw- when clamped tight it's pretty air tight, and vapor diffusion volumes are a function of total area, and the ring hole around each screw will be on the order of 0.02 square inches or less, which is basically nothing.

There are a number of foam-reclaimers operating in your area, and reclaimed foam is WAY cheaper than virgin stock foam, typically 1/4-1/3 the cost of new foam. See:

https://indianapolis.craigslist.org/search/sss?query=rigid+insulation (I'm sure there are others, maybe closer than the guys in Spencer.)

Figure out how much you need and buy 10-15% more than that to cover scrap and the occasional panel that is too damaged to use.