Hello folks. I've been scouring this forum for a while and have a few questions. I wish I had found it earlier...what a resource! It seems to me that radiant heat design, product types and operation can become quite complicated if you let it...and that's my major issue. The more I learn the more unsure I become!

I'm constructing our one story milled (8x8) log home with a full walk-out basement (unfinished). The living area is 1820 sq. ft. 1st floor coverings would be engineered bamboo (floating) and carpet. The roofs are R-54, and the greatroom is 24x32 with a cathedral ceiling. I plan on adding solar later, probably a Sunda collector, and am running the copper lines up to the roof.

I have contracted out the concrete, electric and shell, and am going to do the interior, pex plumbing and hydronic radiant heating myself, because I have to. The concrete basement walls are up, and I'm ready to install 1/2" pex in the basement slab. I'm behind with the radiant heat planning! I figure I would just install the Pex in the slab and leave long leads, as to not hold up the deck, backfill, etc. Should I use PAP here too? I am insulating the sides of the slab, but should I insulate the entire area under the slab, or leave a center heat sink? We're on solid dry clay (aka June concrete).

I thought I had the radiant covered, but I'm unhappy with the 3 quotes I received. I used worst-case scenario of -15F for low temp here in Fort Ann, NY for the heat loss calcs. One company quote called for 81k btu/hr for underfloor joist installation with aluminum plates; another calculated 109.5k btu/hr for above subfloor with sleepers and gypcrete or equivalent; and the 3rd (my local plumbing supply) required 77k btu/hr with Joist-Trak or Quick-Trak (a well-detailed Wirsbo quote). All included basement slab install with 1/2" pex. All required higher circulating water temps than what I had expected, and the third required temps up to 163F with the Joist Trak. Yikes! Or maybe not, because I employed the worst case. Did I err in using -15 degrees for the design temp, and set myself up for shocking water temps? If not, that's quite a lot of enegy to produce.

Being in the 99% category, cost is an issue....not just install and material cost, but operating cost. I'm already way over budget, but I've place a priority on energy efficiency, and am willing to sacrifice elsewhere.

This forum has many discussions on low mass vs. high mass systems, but I'm still not sure which one is better for the NY Adirondacks. We are planning for central air, and I'm wondering if that would buffer the thermal retention of a high mass system when dealing with a cold night/hot day relationship. A high mass above floor system (sleepers with gypcrete, for instance) would require beefing up the floor joists, which is inexpensive and easy at this stage, but a low mass system would just respond faster to swings, correct?

Early on in the planning last year, I contacted the Regional rep for warmboard, and was impressed with the product. It's pricey, and I discounted it as a "luxury" because it would shift a large portion of the radiant cost from me to my subcontractor. However, due to the efficiency of the product, I'm leaning back in that direction. Most impressively, the rep returned my worried call on the weekend, and promised to expedite the layout and quote in order for me to almost hit my timeline for the deck construction. Thsi system would be most efficient and responsive, however, it's still quite an expense for me. I guess I'm still on the fence.

I've read here that the DIY sandwich method could yield similar results at less cost. Is this true, if I were to use 3/4 ply sleepers and, say Thinfin U with PAP? My labor is free, and we will be living in a large 5th wheel on the site so I'll be able to work the late shift!

I'd appreciate any direction you all could provide. Thanks.

Marc "Inna Spin"

Question for you....do plan EVER to use the basement as a living area? Or will it just be for storage and utilities? It looks like the heat loss calculations take both the main level living area and the basement as heated spaces.

Do you have access to the details of the heat loss calulations? Are they done room by room with associated heat loss, tube spacing, GPM flow, and water temperatures for each room?

How extensively (% of the square footage) will the main level be carpeted, and have you calculated the loss with the lowest R-value pad?

Does the 3rd quote (the local plumbing supply place with the 77K loss estimate) have any satisfied customers that you could contact or go visit?

Reasons for the questions are that after designing and installing my own system successfully, I've come to the conclusion that radiant floor heat does not lend itself to a "one-size fits all", cookie cutter approach, and that the ultimate successs of a system depends much more on a design approach that integrates (too a much greater degree than forced air for example) the heating system with the construction technique and expected life style of the occupant.

I think you're on the right track, here, but would really like to see you check out the credentials (like number of successful installations in your area) of the contractors you're getting your quotes from.

Inna-spin...'couple more questions....what are you using a r-value for the 8" milled log walls? Is there any other material going on the interior other than just the native log surface?

Were you able to insulate the exterior foundation walls woth rigid foam before backfilling? What percentage of the "walk-out" basement walls are exposed?

I don't plan on finishing the basement due to the tax "penalties", but who knows? I will have an office down there and we are installing a "mud room" with full bath facilities for sure. It has 5 windows and a door to be installed. The house is worth a lot more with a basement which can be used as living space.

The 3rd quote was very detailed, and was room by room, including floor coverings, gpm, temp, etc. They are a plumbing supply store where my father (a licensed master plumber) has an account, and they sell to installers, rather than end users. They've been in business for ~125 years. We discussed the quote in detail when I picked up the quote. They recommended Watts Onyx tubing, which appears to be a superior product. They used self-balancing manifolds, so loops could match required loads, etc. It was just a complicated quote for me to understand. And my father, who remarked that radiant heat was much simpler 20 years ago!

Interesting that the most detailed quote (and the one from the supplier you potentally trust the most) is also the lowest. Depending on what R-value those milled log walls and (uninsulated?) concrete basement walls really yeild, that's about 20 BTU/hr for both levels.

Probably some upward margin for error there, but not unreasonable. My recommendations, FWIW, are go ahead and put 1/2" PAP, stapled to 2" XPS under the whole basement slab, on roughly 12" centers, keep loop lengths to 200 - 250 ft each maybe looped so you have three or four chances to balance heat delivery accross the different areas of the slab. Bring that tubing up to your manifold where your boiler/utility room is going to be, put a pressure gauge on it and monitor pressure before, during and after the pour. Try to find a concrete guy that can tell you all about the successful radiant slabs they've done...probably can get a good referral from your plumbing supply place. Take his advice over mine.

That slab, no matter how and if it's ever used directly under living space, will be able to either supply baseline stability to the upper level, or comfortable living space, as long as it is controlled separately from the main upper level. It HAS to be on its own zone. You may not ever need to pump very much heat into it...but the cost of the XPS, a few hundred feet of PEX and a manifold is really negligable in the big picture.

As for the DIY sandwich, I'd say go for it, but you might want to re-read some of my previous posts about the amount of work and knee damage you'll be up against.

Also, sandwich is a decent installation method and often worthwhile in a DIY situation, but it does NOT rival Warmboard's performance. It is good.. better than quik trak, for instance.. but you'll probably be a good 20 degrees over WB's numbers. We love sandwich, just don't want you to have the wrong idea.

Thanks guys.

My basement is planned with two zones and ~200ft loops.

Today I received a quote from another well repected plumbing supply company, and the heat loss calcs practically mirrored the 3rd one I got. That made me feel much more comfortable. The price was respectable, but the quote did not incorporate the use of any heat transfer plates for under-the-floor installation (of Watts Onyx). That puzzles me....why transfer heat by utilizing just the top side of a tube?

As for Warmboard, I know it's the best. I just can't seem to make the leap toward that expense layout given the budget I am left with....but I absolutely HATE settling for less! It kills me!!! However, I've uncharacteristicly developed a reluctance to laying out large sums of money.

Why, you may ask?

Briefly, it took us 1 year and 3 months to close on the property, another year to get a subdivision and an agricultural easement modification to build. During that time, money flew out to attorneys, engineers and surveyors, and housing prices shot upward. We are left with significantly less money to build with. To boot, our rental landlord went bankrupt, the house went into receivership, sold in one day, and we have to be out in two weeks. We had to buy a used 5th wheel to live in, because there is absolutely nothing here to rent. My wife and I, two bird dogs, and a crazed cat in a tin can. Gonna be tight!

But I digress....I guess the questions are: How much more money would that extra 20 degrees cost me over time, and will I lack that extra temp headroom when it gets cold? Can I build a sandwich with substantial heat transfer media (home-made, if necessary)which could rival Warmboard for significantly less?

Thanks.....

best you can do for home made is a Thermofin U sandwich. But then the cost differential gets smaller, and you're still not quite where warmboard is. However, it's also a quite capable system.

The higher temps may or may not be an issue, depending on your loads and flooring and heat source. If you were doing solar, for example, you want to get that water temp down as far as you can.

Inna spin,

I am currently getting quotes for my new construction from radiant installers and I am finding that I am getting very high prices from installers that have not used Warmboard previously. I believe (not positive) that they are figuring on the same labor as a staple up and then adding the price of the Warmboard. I have talked to a radiant installer that does a lot of warmboard and his pricing is close to the pricing of staple up and gypcrete. It is less labor intensive to install warmboard, so the increased cost of the warmboard product is nearly offset by the reduced labor costs. My GC is going to lay down the Warmboard in place of the subfloor, so that is not figured in the radiant price. For me it is a no brainer, because I am not doing any of the labor. For you though, the labor is where you are trying to save money, so it will be more expensive, but for future solar use (I am also considering that), Warmboard has the lowest temp requirements. I have decided that I would rather put my money into the warmboard now and wait a little while on some furniture purchases, landscaping, etc. Those can be done later, but you cant upgrade your heat later.

Just my .02

Thanks. I really appreciate the thoughts. All made good points regarding the low temp/solar relationship. You're right Jeff, I can't go back and install warmboard. I've asked for a professional comparison of sandwich vs. warmboard, something that I cannot figure out myself. Then I can make a solid decision. But I'm leaning further towards the warmboard due to all of your help. Thanks again.

what about gypcrete/thermafloor pour? How much better is warmboard than a pour of thermafloor, or sandwich with heavy gauge plates.

I'm in a similar position with plans to go solar down the road.

Inna spin

Log homes can be a tough one on heatloss calcs.
Also your walls are an r-8 at best with an 8" log depending on wood species. Thats the bummer of full timber wall sections let alone infiltration which is a big hit in a heatloss calc....This may be why you are getting different ranges of btu losses.


You should use the design temp for your location. This temperature is only reached about 1% of the time during the heating season.


As far as warmboard remember it is replacing the subfloor you would be laying instead of warmboard so deduct that material difference out of your comparison.

Labor wise the panels are heavier, and there is some thinking/planning involved so the framers are going to hit you for that if they have never done warmboard installs.


All in all its superior, and if you can scratch to get it I would. You cant beat the heat transfer of a continuous sheet of Aluminum.


Gordy