G'day,
  I'm considering installing radiant floor heating in our master bedroom and bathroom.  The home was originally designed for passive solar heating assistance.  As such - part of the room (about 250sf) has a 2" concrete slab poured to absorb daytime heat.  This slab has a basement underneath it, so is not slab on grade.

  If I wanted to tear up the existing tile and install hydronic radiant floor heating - how do I go about adding that on top of the concrete already there?  I can get to the floor underneath, but wonder if there is too much material going on for an effective heat transfer.  The floor is supported by joists, then a plywood subfloor, and then the concrete on top.

Sean.

A 2" slab isn't a big deal to heat from below using the same aluminum heat spreaders used with wooden sub-flooring. You'll still want at least 3" of fiberglass or rock wool snugged up to the under side of the tubing & heat spreaders to keep it from overheating the basement though.

The thermal mass of the 2" concrete will add a bit of delay to the response time, but it's R-value is still quite low- R0.2-is unless it's some super low-density stuff (which might be as much as R1), but in general 2" of concrete is more thermally conductive than say, a layer of hardwood flooring.

How many sf of floor in addition to the 250 sf do you need to heat? You can do as Dana suggests for the existing 250 sf, but the supply temperature to that area will be much higher than if the PEX was directly embedded in the concrete. You could do thin slab in the remaining area, but you would have to verify that your floor structure is adequate. Thin slab would provide best performance. Next best would be some above floor system such as Warmboard or RHT. Have you done a room-by room heat lost analysis so as to be able to properly design the hydronic radiant floor heating system?

Hey Folks,
Thanks for the replies. I would have thought the plywood subfloor would provide too much insulation from the pex underneath to adequately heat the concrete above it. Glad to hear otherwise.

I have not done a manual J yet - but it is on my list of things to do. Total square footage is 500sf give or take, cathedral ceiling. 250sf of it is currently tile on the 2" concrete. The other 250sf is currently hardwood on a plywood subfloor. Intention is to rip it all out and tile the whole thing.

My thought process at the moment is to heat via a radiant floor and cool via hydronic fan coil units. I like the sounds of the Chiltrix air to water heat pump (CX34).

Part of my motivation to moving to hydronic is that we run a rescue for giant breed dogs out of our home. The pet hair and dander wreaks havoc on a centralized ducted solution. While the room based fan coil units will also get dirty - I can clean them, and or replace them individually without compromising the rest of the system. As the units are stackable - I figure I can grow the system until I eventually do the whole house.

Current heating and cooling is via a 3 ton air source heat pump for the whole house.

Sean.

Posted By sailawayrb on 28 Feb 2017 06:58 PM
Next best would be some above floor system such as Warmboard or RHT.

For the regular portion of the floor - I was going to go with an above the floor solution as you mention. I had looked at the warmboard solution and other similar products, but I find the cost extremely prohibitive - over $6 per sf for the materials alone the last time I looked. My plan was to do more of a DIY solution using ripped strips of plywood and the aluminum heat plates for a similar effect.

I'm not sure the non concrete portion could support a thin slab - I'd have to take that up with an architect \ engineer.

Both sections have a 16 foot span on the joists. The concrete portion has 2x8 joists 12" OC, supported by a triple 2x12 beam in the middle. The hardwood portion uses 2x10 joists 16" OC with no beam. A beam *could* be added if absolutely necessary.

Sean.

Static Dry R-Value is the last property if at all to consider here. You are being HIGHLY mislead! What ppl get for free most of the time.

You have to think in terms of wet U-Value. When one does a 3,000 PSI mix is quite conductive & fast reacting @ water contents to 10 lbs/FT3. Higher PSI or binder/OPC less. I'm guessing 3000 PSI and rebar is taking all the clear span loads. Usually there is a 2X margin and some wiggle room. If you know the rebar size you can verify to code. If there is margin adding more dead weight may not be an issue. In any case it s/b low density to up MAX Water Content (MWC) for higher thermal conductivity as an upper screed that can take walking compression loads 200-lbs/SF code IIRC. That is a distributed load.

Plywood can be more thermally conductive than concrete w/a MAX MWC @ 25 lbs/ft3 but it needs to dry in less than 24 hrs or it rots/delams. OSB is a little better and lighter. Solid wood flooring like Eastern White Cedar or Pine is more thermally conductive than concrete at high MWC.

Of course, when a composite is designed the properties combine in a way that takes Engineering.

PEX is a poor conductor, best DIY approach is get a local shop to extrude 1100 series ALCLAD, then HT to T3. Forget the plates they won't be as conductive nor as lite/strong especially along the grain. Agree, those products to make PEX more conductive are ridiculously price only fools buy into it or recommend them and there is no guarantee how effective they are other than pro-claimed consumer reports that varies. AL is 200xs more conductive you can make your lines out of 1100 series. Copper is 400xs more.

CX34 is ~$3000 over priced compared to a minisplit. Other than easy HR connections I don't see the value yet anyway & it's low temp COP got worse. Back-up water is nice but not that nice.

I have no affiliation with Chiltrix - and I'm not necessarily sold on this particular product, I've only looked at their products online. But... How is it $3000 over priced when the unit only costs $3800 to begin with? You're saying I can get a 2-ton cooling, 3 ton heating mini split for only $800??? I certainly haven't found that system in my travels... I also have no interest in installing a system that requires a refrigerant technician for the installation, hookups and servicing. One of the prime selling points to me on a hydronic system is the ability to self install and self service a large portion of the system. Every dollar I don't have to give someone else is two dollars I didn't have to make in the first place.

Aluminum and copper may be more conductive than PEX, but they are also considerably more expensive. I'm not an installer and I'm not in the business - but I've only ever seen pictures, videos and installation manuals of radiant floor heating being installed with flexible plastic tubing of one variety or another.

Sean.

We have free DIY heat loss analysis and hydronic radiant floor heating system design software on our website that you might find useful for your project. You might also find RHT to be a good above floor solution too. Dan from Blueridge contributes to this forum on occasion and would be a good resource for this. Yes, O2 barrier PEX is what you should use.

I like the sound of the RHT product. Half commercial (rounds and plates), half DIY (plywood rips). Assuming the use of RHT panels and plates - do you need to install an additional layer above before putting down the tile adhesive and tiles? My assumption would be yes - looking for confirmation. I'll take a look at your website for the heat loss calculator you mention. Thank you for that. Sean.

Posted By sdboers on 01 Mar 2017 09:44 AM
I have no affiliation with Chiltrix - and I'm not necessarily sold on this particular product, I've only looked at their products online. But... How is it $3000 over priced when the unit only costs $3800 to begin with? You're saying I can get a 2-ton cooling, 3 ton heating mini split for only $800??? I certainly haven't found that system in my travels... I also have no interest in installing a system that requires a refrigerant technician for the installation, hookups and servicing. One of the prime selling points to me on a hydronic system is the ability to self install and self service a large portion of the system. Every dollar I don't have to give someone else is two dollars I didn't have to make in the first place.

Aluminum and copper may be more conductive than PEX, but they are also considerably more expensive. I'm not an installer and I'm not in the business - but I've only ever seen pictures, videos and installation manuals of radiant floor heating being installed with flexible plastic tubing of one variety or another.

Sean.

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Good you have no affiliation with Chiltrix – This site and others like GBA are plagued with self-promoting or product promoting sales trolls that like SALIAWAY are always point to their site to promote services claiming to “help the DIY” BS, or, we have GBA blog writer DANA 1 where they push lots of foam products. They team up promoting each other. You’d think the mods do something unless they pay a fee, I don’t know how this site works. People like this trying to makes sales puts the focus on them or their products not necessary to more cost effective design solutions. Often, there is little data to back the claims.

For heat loss get with your local installer.

I get ~ $3,000 more for Chiltrix minus CCHPMS back up 3-ton  John there is good with the product but I had to update him to the latest CCHPMS tech like being able to daisy chain and couple HRVs it can’t do and the 3 ton system I compared removes latent heat to better COP cooling too. I need to get back on GO TO with him he thought there is justification for the $3K but we had to get the bid in fast. On my list, it does look like a good product but they improved range COP and lowered CC(cold climate) COP a tad which may not be a big deal. If the unit is close to a boiler it has on board connections. It can also heat DHW the pump switches but compare that cost to whole-house on demand it can also connect to as seen on their shematics.

One owuld have to add the cost of RHT the better solution since there is alot of AL $$ there not far from lines with end ftgs, once could just find some AL lines with or w/o end fitting then compare that cost to AL $ Copper that would not need as much material & BTUs/HR.

Sean, I would recommend contacting Dan directly and working with him to sort out how best to use RHT for your specific project. We have not personally used RHT, but we have heard from folks who have used it and are happy with it although it is somewhat more labor intensive than Warmboard. We don’t get involved with remodels and all of our HR installation work is new construction placing the PEX directly in concrete.

With any heating project it pays to run careful heat load numbers before specifying the solutions, especially when looking at higher-cost radiant options.

Getting adequate heat through a subfloor can (most likely) be done cheaply, but it does increase the water temperature requirements relative to more expensive above-the-slab solutions.

Only when you know the range of water temperatures you will need and the magnitude of the can you make intelligent choices as to whether air source chillers are even on the table, let alone a "right" solution by any measure, or whether some other heat source (at some other price point and design-risk) makes more sense.

One would have to deal with alot of clients on daily basis and actually design-build-sell high performance homes and products to know this which is not the case in the last two post. Easy to suggest $6-8/SF or perhaps $10-25K in HR cost + cooling when it's not coming out of your wallet while at same time not relating a pay-pay period or how to appraise the value for initial sale or resale. Clients IF you have any experience with them, most, or the banks want to know a justification for such cost, smart people with all cash too. If you have no idea what the design choice will have as a utility bill by annualized cost over some term, there is no way one can make sense out of any high tech solution when compared to central air/furnace mainstream cost is very low like 5 ton/100 BTU/hr w/low cost envelope. If a local appraiser will not or does not know how, since there are no comps, all cost will be lost don't waste your time saving DIY your money ends up in the toilet. Perhaps people with cash don't care, then why are they working for $10-15/hr DIY just hire a trade your money will be lost anyway.

The only way around this is by competent tech/financial design models 99% of the people out here don't perform since they don't have the right softwares or knowledge. On the tech side for HR if the software does not include fluid dynamics or properties such as u-values at different moisture contents for solids vs dry static r-value as suggested above, and as I said a related annualized cost with a utility bill savings to compare or cost optimize the tech solutions and offer a report to an appraiser and client it is worthless!

The other issues with clients is they highly value aesthetics over performance. Chitrix air handlers are ugly, I can't sell them, they need to be flush mounted for example. I can sell them to a commercial client but not residential. I'm currently going around in circles with a client that wants exposed ducts and trusses, so the ductless MSHP I suggested may be out unless I can satisfy with ducted ERV. I spends mounds of time writing reports to clients to explain the unknowns with HP homes, and it does not pay for my time for customs. We just got done with two bids, one mainstream junk, one 10% more in construction cost for HP and I gave a estimated utility bills of $150/mo saving for the HP option in a 6 page report. Waiting to hear clients choice. If they choose HP I have to spend mounds of time with their appraiser educating on the value of high insulation, MSHP, ERV, HR they want I have to try an make sense of a cost that will push it into negative cash flow and equity if the appraiser is not on board, there are none that are AI qualified within all surrounding states in the central plains here and we checked 36 states with one big bank.

Perhaps l may be able to get the HR in with Chitrix combining more sub-systems......last resort I doubt it.

The best way out if all is specs but again getting appraisers and banks on board renders them cost prohibitive in most parts of the USA since higher 5-10% initial cost has to be compared to and appraisal using an ERI score and AGREEA annualized or it goes nowhere! I got a feeling I just lost you two above....

I'd like to see a design model or build you are doing or talk so much about Saliway and how it appraised???? Since I don't believe you nor should anyone else since I can tell by your post you don't design-build-sell performance homes like you claim nor do you D1.

Well if I confused the hell out of this client and we don't get the build, D1 are there any job openings over at GBA writing BS blogs and selling foam in Q&A? Then I can tell DIYs what to do w/o any experience doing it nor liability and I can drop my E&O/ The Green Life must be good at GBA :)

Good Lord I wish this site had an "Ignore" button.

Wow!

Hey Folks,
  So I found a great site for Manual J calculations (www.coolcalc.com) and input all of my data as accurately as I could (I hope!).  I generated a PDF of the results and have attached it here (again - I hope!).  What I *think* I'm reading from the bottom graph is that a 3-ton unit is about right for our home, 4-ton would likely give a nice margin of error.

  Happy to have anyone correct my interpretation of the results - this is new territory for me.

Sean.

Sorry - I should note - that is a whole house manual J - not for the 500sf I originally posted about!!

Step 1 would be to upgrade heating and cooling in that 500sf. Step 2 would be to change over the whole house.

Sean.

Looking over the Manual-J those are some pretty big numbers- how big is this house?

A couple of comments:

Wall losses from the below-grade walls are more than 2x that from above-grade walls, which implies that the basement walls are not insulated(?). That's something worth doing even if you aren't converting it into fully conditioned living space.

The infiltration is also 18.7% of the total heat load. With a round of blower door and IR imaging directed air sealing you should be able to get that down to a single-digit percentage of the total.

House is about a 2200 sf bungalow - so another 2200sf in the basement. To address some of your points and comments:

1) in the calculation I left the basement walls as uninsulated to be pessimistic. About 1/3 of them actually are uninsulated - the other 2/3 I don't think are insulated particularly well. I'd have to pull drywall off to be sure.
2) The house is leaky - very very leaky. I am taking steps each year to start closing up the envelope, but it is an expensive - and thus long process. The windows are crap and all need to be replaced - I'm part way through that. The walls are double wall construction - which in theory is great. In practice on this house - the thermal gap between the inner and outer wall actually overhangs the foundation - allowing significant air penetration from underneath (critters too). I'm fixing that bit by bit as well. Once upon a long ago I did a blower door test. If I recall - it calculated the equivalent of a 6x6 hole of air exchange.

I'm going to install external solar shades this summer in an effort to limit the amount of solar gain which my cooling system then needs to dump.

Sean.