Loghomebuilder, you do realize that air-source heat pumps (i.e., like used in mini splits) are also available for heating hot water for HR heating systems? Ground-source heat pumps (AKA Geothermal) will heat hot water too. In theory, ground-source heat pumps should offer significantly higher performance than air-source heat pumps, especially in cold climates. However, ground-source heat pumps are more complicated systems than air-source heat pumps and as a result they are often more expensive and more prone to have operational issues. Both air-source and ground-source heat pumps will significantly out perform boilers. You might want to research the Geothermal forum to get better informed. We do have free DIY software on our website to determine the operational cost of the various heat source options being considered given your actual fuel option cost:

Borst Integrated Heating System Performance Software

Posted By sailawayrb on 18 Aug 2016 09:57 PM
Loghomebuilder, you do realize that air-source heat pumps (i.e., like used in mini splits) are also available for heating hot water for HR heating systems?

No I did not realize that. I will check out your website.

Yes, a Daikin Altherma would be one example of an air-to-water heat pump that can be used for HR heating and DHW heating:

Daikin Altherma

There are many other examples and you do have to confirm that the unit you select will output the required amount of heat at your expected outdoor cold temps.

It doesn't look like those systems work much under 40 degrees. That simply wont work for me. How do you keep concrete from cracking in a suspended slab design? is that not a risk? I am now leaning towards something like this, the voids filled with concrete, or some other dry mix material (suggestions welcome). This seams to be the best combination of easiest/best/most cost effective system for a DIY person like me. Using 3/4" sleepers would only add 9 pounds per square foot of weight and run $450 in concrete if my math is correct. I could use larger tubing with larger sleepers etc. Thoughts?

I cant seem to get the image to upload, here is a link, Next to the bolded letters "Use 2x4 Sleepers"

http://www.radiantcompany.com/details/methods/suspended/

All concrete cracks to some extent, however that doesn’t normally create any risk or problems associated with HR design or structural design. Yes, if you feel compelled to accomplish a DIY sleeper HR emitter, that is certainly an option you can pursue. However, this option will not perform nearly as well as having the PEX directly embedded in a concrete slab. This is well established and well documented by John Siegenthaler’s “Modern Hydronic Heating”. I also suspect that the cost to design/build the floor structure to handle standard/thin slab and the cost to hire someone to pour standard/thin slab would be competitive with the cost to accomplish a DIY sleeper HR emitter. Anyhow, this is something that you will need to sort out on your own given your specific locality costs and make a final determination.

I am not sure where you came up with a 40F operational limit? Air-source heat pumps can typically perform well at and often beyond 0F. When designing a hydronic system for a heat pump, it’s imperative to keep the required water supply temperature as low as possible. This implies using slab-on-grade or thin slab HR emitters in lieu of below-floor plate HR emitters and also minimizing floor finishing R-value, which results in significantly lower required water supply temperature.

You might find this John Siegenthaler article quite enlightening relative to air-to-water versus ground-to-water (Geothermal) heat pump options and relative to what I wrote previously:

John Siegenthaler Reviews Heat Pumps

What do you mean by " DIY sleeper HR emitter"

I am talking about putting the pex in a thin slab, with wood sleepers so I can stable hard wood flooring to the sleepers.

Sorry, I made the mistake of looking at the Radiant Company link that you referenced...sleepers, sand and plates, etc...some sort of "DIY sleeper HR emitter"... I suppose that when there's enough money and time, most anything is possible!

Using Gypcrete for HR works very well, depending upon the floor finish. As you add more floor finish R-value, your required water supply temperature increases. As I wrote previously, higher required water supply temperature begins to create efficiency problems for the heat pump HR heat source options. If the required water supply temperature gets high enough, even condensing gas boilers will lose efficiency. The required water supply temperature also depends on the desired room and actual outdoor temperature. So you really need to first accomplish a heat loss analysis and HR design to sort out the required water supply temperature before selecting your heat source. You also might want to take a careful tally of ALL the costs associated with the ALL the options that you are considering. The cost of the Gypcrete (or plates) and the sleepers might start making WarmBoard look more attractive and reasonable...

When accomplishing new construction, most folks take an integrated design approach and consider/trade all the things that they think they initially want in a way so as to achieve some compromised overall goal that makes them happy for a cost that is reasonable to them. If you want low cost and maximum efficiency HR heated floors, you consider building designs that will utilize concrete floors. That way your concrete cost creates both the floor structures and the HR emitters for minimal cost. Then these people either use polished/stamped concrete or tiles and area rugs to finish their floors to maximize heating efficiency. The issue I see here is that you want lots of wood (i.e., a log cabin and wooden floors), HR heated floors, high efficiency, and cheap. If you are truly compelled to build an inefficient log cabin having wooden floors, I would suggest that you should perhaps consider something other than HR floor heating if you really want to improve your heating efficiency and associated operating cost. Mini splits, masonry heaters and wood stoves come to my mind... If you are willing to give up efficiency (and you are proposing building a log cabin on a Green Building forum after all), then just do the sleeper thing or the WarmBoard thing...but don’t expect it to be efficient or cheap...

I'm sorry I haven't been more clear. This is a log home but it will be efficient. Sure it wont be super insulated or as tight as an ICF house but this is not the kit-style home you may be thinking of, which usually are filled with gaps and air leaks all over. This is different. Because its not widely done and not commercialized, I dont have any hard data to show you however, a friend of mine built one exactly as I am and he didnt even run radiant on his first floor at all, he says the heat from the basement slab is enough to warm the basement, first, and second floor. His is a weekend place, mine will be year round, so I don't want to rely on that for even heating.

I got a quote for warmboard and its $12,000 plus tax, plus shipping, compared to maybe $900 bucks for a normal subfloor. So that is out of the question. I can't seem to find any company that sells Rauhpanels, AND get them to call me back.

I am simply trying to compare the additional monthly energy costs of staple up, to the energy savings costs of another system. I like the idea of the sleeper system, but have never worked with gypcrete, and am not sure what the extra weight would mean for me structurally, so I can't exactly compare those costs on my own. That link above says dry sand is a great thermal mass, I have read that its not good for radiant systems though, and in my experience sand is a great insulator. A drypack mix with portland cement seems OK too.

Gypcrete thin slab adds about 15 psf to the floor loading. This can usually be easily and affordably handled by reducing the floor joist spacing and/or increasing the joist depth. A few hundred dollars for engineering and a few more hundred dollars for the additional lumber should get the floor structure done. Then just the expense of pouring the Gypcrete...which will be way less than Warmboard. Perhaps float engineered wood floor over the Gypcrete...and use a vapor barrier.

Having designed and installed both systems in several states over a couple of decades I can tell you that the installed cost of Warmboard and any cementious system in most markets is going to be close. Since both are mature markets you will find competition driving cost close.

Maxxon or Hacker Industries can give you all the information you need for rough comparison and referrals to local applicators with "real" numbers and experience.

http://www.maxxon.com/therma-floor/data

http://www.hackerindustries.com/gyp-span-radiant.shtml

Once you back out the cost of a 3/4" sub-floor--included in the Warmboard panel, you may find it a bargain as I do in many of my designs where sound attenuation and fire protection are not a concern. If you decide sleepers are required for solid wood flooring installation it will be tough to justify the considerable work involved and the up-charge you will likely see from the gypsum applicator.

No one can tell you what it will cost with any certainty, least of all someone whom has never designed or installed such a system.

We design both systems regularly but never suggest one over the other without homeowner input and local bids.

As to the cost of operation. The main factors in operation cost of any radiant system are heat load, hat source, floor covering and the distribution system. From your description the cost of operating one system or the other would be very similar and certainly not predicable without a computer to model each system by. We have such dedicated software.

In my experience "log home" and "efficient" have yet to belong in the same sentence (and I've yet to even bother looking at those crummy kit houses.)

The seasonal dimensional changes with temperature & humidity of wood makes log homes difficult or impossible to air seal to truly efficient levels in a way that retains that air tightness over a handful of years. If there's a way to really keep it air tight over the long haul I'd like to know how that's done!

Ya gotta use really good mud

Well, I think the OP is willing to trade the building efficiency to have the log cabin. The OP also really wants a HR heated floor. If it was me, I would probably do a concrete deck over the ICF basement. I would also concrete color/stamp this deck in a nice bluestone, heavy stone, or slate and it would become the HR floor for the log cabin. I bet this would be cost competitive with the other lower performance options.

I'd probably skip the basement, use a frost protected shallow foundation slab and make the garage larger to get more storage space. Maybe try to seal leaks with EPDM spline gaskets. Or build a stud wall inside of the logs.

Posted By jonr on 25 Aug 2016 08:13 PM
I'd probably skip the basement, use a frost protected shallow foundation slab and make the garage larger to get more storage space. Maybe try to seal leaks with EPDM spline gaskets. Or build a stud wall inside of the logs.

Ditto

Yes, that would be a much cheaper way to get the job done. As long as it is kept heated during the Winter, it shouldn't have any frost heave issues. However, the OP would have to be willing to trade the basement too... Now if the OP was willing to trade the log cabin for an ICF single-story ranch style home, this could be an extremely efficient building...

I'm back! I'm now at this stage of our build. I am told my Manual J is 54,600 Btuh heat loss @ -9 degrees OAT....whatever that means.

Basically I am getting down to the wire.....is it staple up with plates or a sandwich system. Staple up with aluminum plates has 3/4" subfloor then 3/4" hardwoods. I would insulate the joist bays from below. Sandwich would be the same 3/4" subfloor, then a layer of radiant barrier, furring strips with channels for tubing, the same aluminum heat plates and same 3/4" hardwood flooring.

The main difference I see is, in the staple up method, the aluminum plates have an air space on their bottom side, so heat only flows upward. Whereas the sandwich method, there is contact with the aluminum plates on both sides, top and bottom, as well as extra wood (the furring strips) that would need to be heated. Wouldn't this draw more heat downward, and reduce efficiency??? I guess the benefit is that the aluminum plates contact the finished floor directly. But which is advisable in my situation? Staple up with plates or sandwich? "Best" in this scenario I mean long-term energy costs being most important. I can easily pursue either route moving forward, and I assume there is an agreed upon answer......

One more thought, the advantages of a warm board system, I am told, is lower water temps means higher efficiency. Well, how much higher, exactly? And how does the equate to actually dollars spent? Are we talking 5% more money spent on heating fuel per month? 25%?? 50%???? Also, cant you use larger diameter pex to achieve lower water temps??? I have the ability to use 5/8 or 7/8 pex without a problem. Piping could be spaced tighter to further lower water temps. Does changing the piping variable help me with efficiency?

I think you should work with Dan from BlueRidge Company on this. They have an above-floor sandwich system that should work for you and they have much experience with this type of HR emitter.

I would not recommend below-floor staple up because it is extremely inefficient. The most efficient HR emitter is a standard concrete slab followed by a thin gypcrete slab. Warmboard is likely as efficient as as a thin gypcrete slab, but on the pricey side. Really, once you need aluminum plates, etc. to get the heat to move upwward, things start getting pricey.

Try to keep the R-value of any material above the PEX tube to a minimum (e.g., wood, carpet, etc) to maximize efficiency. It is the ratio of the R-value above/below the PEX tube that determines the efficiency of a HR emitter. So placing much more R-value below the PEX tube (i.e., add insulation) than is above the PEX tube will improve efficiency. The goal is to not allow more than 5-10% of the heat provided via the PEX tube to flow downward. Of course, the performance of the building and the heat source are also important in terms of minimizing energy use and associated operational cost, which is ultimately what one should care about.

54,600 Btu/h @ –9 OAT means that your building heat loss is 54,000 Btu/h at –9 deg F which is presumably the correct 99% design Outside Air Temperature where this building is located implying that it will only get colder than this 1% of the time. A proper HR system design will determine the PEX tube size/spacing and zoning that will deliver the amount of heat each room requires at the lowest supply temperatures and lowest flow rates. You first need a room-by-room heat loss analysis which is presumably what your ACCA Manual J8 heat loss analysis provided. A proper HR system design should define all the required HR system components (including heat source options), supply temperatures, flow rates and acquisition/operational costs.

Yes, I have reached out to Dan and gotten a quote from him some months ago. That is likely the way I will go if I go the sandwich route. So the consensus is above floor sandwich is better than staple up?? What about larger sized piping to keep water temps down??

I had only ruled out gypsum or lightweight concrete as an option because I cannot find a supplier in my area, but the research I did seemed to show gypsum was much more costly than sandwich. Gypsum though seems like it would be less work than the sandwich. also I am not positive that my floor joists are strong enough. I have 2x10 #2 fir spanning 14 foot at 16 centers. plus then there is the steel beam...