Radiant insulation + concrete
Last Post 30 Sep 2014 10:58 AM by sailawayrb. 11 Replies.
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Vancouver123User is Offline
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13 Sep 2014 11:24 PM
Hello, we are retrofitting our house with hydronic in-floor radiant heat. The ducts have all been demo'd so this is a go. We've got two floors. To get heat to the second floor we're putting tubes between the joists in the ceiling of the basement (with reflector shields). For the basement different plumbers have told us different things - either: (a) putting a couple inches of foam insulation on top of the existing slab, then the PEX tubes, then concrete on top. (b) putting the PEX tubes directly on the existing slab (with mesh to hold them in place), then concrete on top. Our preferred guy recommends (b). Any thoughts? Also, the new concrete pour will significantly bury the existing wood framing. I understand that wood touching concrete is bad. How is this typically handled? Thank you!
sailawayrbUser is Offline
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14 Sep 2014 09:59 AM
We would first recommend getting a copy of John Siegenthaler’s Modern Hydronic Heating and get somewhat educated on this subject. You first need to do a proper hydronic radiant heating system design to determine the required supply temps, flow rates, and PEX size/spacing for the circuits. Before you can do a hydronic radiant heating system design, you first need to do a proper room-by-room heat loss analysis. We have free DIY heat loss analysis and hydronic radiant floor heating design analysis software on our website that you might want exercise after first reading the associated instructions:

Borst Heat Loss Analysis Software

Borst Hydronic Radiant Floor Heating Design Software

Hydronic heated concrete slabs should always be insulated. As a minimum, you don’t want more than 10% downward heat loss of the total heat supplied to the slab. Insulation is placed below the concrete slab and around the slab perimeter between the slab and the wall. Use of insulation should mitigate having concrete coming in contact with wood. We would recommend using EPS for the insulation as it is more green than other insulation products (e.g., XPS). Our aforementioned HR software will determine and advise the minimum insulation R-value that is required. You may want to use more than this minimum insulation R-value to further reduce downward heat loss and associated monthly heating bills.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
ICFHybridUser is Offline
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25 Sep 2014 10:23 PM
Our preferred guy recommends (b).
If he's trying to avoid insulating the concrete slab, then get a new guy.

You might consider a Schluter product called Bekotec down there. It's a foam board with knobs that also hold the radiant tubing and lets you do a dry pack cement on top, then the regular flooring. The Bekotec gives you a small amount of integral insulation, but what you do is put any amount of EPS foam board under it to give your desired insulation level. You get a minimal floor height increase.

An added benefit is that your "slab" will be high and dry with no chances of passing moisture to the bases of the studs.

Bekotec should not be unheard of in Vancouver. My supplier says that the majority of his sales go up there.
Vancouver123User is Offline
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27 Sep 2014 12:37 AM
Thanks - as we've gone down this rabbit hole we've been leaning towards Uponor's Fast Trak. Any experience with this product?
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28 Sep 2014 11:31 AM
Reading your post I wanted to know if your slab is insulated? That to me is a pretty important piece of information. If it the Uponor's Fast Trak seems like a good fit but if it isn't then the reading I have been doing indicates an R-10 EPS would be a good idea. I am planning to build in a few months and will be using some product most likely Nudura for an R-10 floor for the areas that will get hydronic heating.
http://www.nudura.com/docs/default-source/brochures/hydrofoam-information-sheet.pdf?sfvrsn=4
It looks similar to Bekotec but I have no information to indicate one is better than the other.
I only am thinking of Nudura because my ICF are all Nudura.
Love to hear which product you choose and some pics too if you decide to take a couple during your install...
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28 Sep 2014 01:17 PM
Yes, a HR heated slab must be insulated as previously discussed. There are HR emitter performance benefits for minimizing the R-value of the material between the PEX and the finished floor surface that should be considered too.

Since we are in the business, we don’t use expensive products like Bekotec or Nudura for insulating slabs and simplifying the placement of PEX. We use lower cost Type II EPS and more of it than is normally called for so as to reduce the downward floor heat loss to 5% or less of the heat supplied to the floor. In the past, we would just properly tie the PEX to the rebar or WWF (depending on the structural engineering reinforcement requirements of the slab) and lift both the reinforcement and PEX to the center of the slab during the concrete pour. More recently we have been chairing both the reinforcement and PEX so it will be located in center of the slab prior to the concrete pour. We fabricate our own chairing system which also allows selective inducement of control breaks where needed without having to manually cut them.

Speaking of control breaks, that’s another issue that should be considered and properly addressed. We always sleeve PEX wherever control breaks will be located. Again, getting a copy of Sigenthaler’s Modern Hydronic Heating and getting educated on this subject would clarify many of the issues that you are now thinking about and, perhaps more importantly, many of the issues that you have not yet thought about...

Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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28 Sep 2014 09:58 PM
In the past, we would just properly tie the PEX to the rebar
What about retrofit situations? I'm also curious if you have had the opportunity to do a cost comparison between Bekotec and any other methods (in retrofit situations).
We always sleeve PEX wherever control breaks will be located.
Have you seen any disasters in places where sleeving was not used? I mean where rebar and not mesh is used? I didn't do any sleeving and if I had to do it again, I might have sleeved, although we did make sure that all slab junctions were extensively crossed with rebar. I didn't do any crack control on some large slabs. I have hairline cracks, as expected, but I feel pretty comfortable that the rebar ensures nothing is moving.
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28 Sep 2014 10:53 PM
I drilled some exploratory holes, looks like we have a 3" uninsulated slab. So I think the R1.7 Fast Trak will be inadequate. So I'm looking at Creatherm (R5, 1.8" height including tube) or Crete-Heat (R6, 1 7/8" height). Thicker insulation could be better but we currently have 8' ceilings in the basement but I'm reluctant to lose much height.

The quotes I've received from plumbers have been quite high and as I'm learning more I'm getting more confident and thinking I may DIY it - hire a company to design the system, then source the product myself and install, and have a plumber come by at end for plumbing connections and testing system. I'm in Canada where plumbing supplies are not available cheap so would have to source from supplyhouse.com and others and drive across border to get.

To install Joist Trak myself (if needed, I'm in Vancouver which is mild climate), lay down one of these pre-fab floor systems, run the tubes based on a professional's design, source the boiler/indirect tank, and get a plumber to hook it all up at the end... looks like I'd save around $10k and doesn't seem like rocket science...



The other thing I could do is forget about in-floor in the basement, and use a slimline hot-water baseboard like Rescom 2100, but I don't think much savings would result and the only benefit would be no ceiling height loss.
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29 Sep 2014 10:45 AM
as I'm learning more I'm getting more confident and thinking I may DIY it
Another reason I liked the Bekotec was because you can do a dry pack slab over it. It was very easy to DIY. It didn't require a slurry pumper or gypcrete contractor.

The other thing I could do is forget about in-floor in the basement
How cold is your basement floor to the feet as is?
sailawayrbUser is Offline
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29 Sep 2014 11:53 AM
ICF, we don’t get involved with retrofits. We only do new slab construction. So we can’t comment on cost comparisons of retrofit products. My original point was that we wouldn’t use these more expensive retrofit products for new slab construction. However, I now just realized the OP already has a slab, and it is apparently not insulated...  So these retrofit products would be entirely appropriate for this project.

ICF, with regard to sleeving the PEX in the slab you described, I don’t think you will have any issues. A well-reinforced slab with the PEX tied to the rebar is not likely going to crack and move enough where the PEX is located to create the required stress to damage the PEX. Damaging PEX is more an issue (reportedly by Siegenthaler) when passing PEX through intentional control break areas. Control breaks may see cracks and concrete movement in excess of a 1/4". So this is why we follow Siegenthaler’s sleeving recommendation. We have never experienced any failures when doing this. We have heard that some folks don’t bother doing this and they have not experienced any failures either. However, we have not been brave enough to NOT accomplish this control break sleeving. Having provided expert testimony witness, we have seen first-hand what happens to contractors who have not followed accepted best practices when customers subsequently take them to court to resolve problems.

Vancouver, there is nothing to fear about DIY! Just take the time to learn how to properly do it and then expend the effort to properly do it. We have all the required heat loss analysis and hydronic radiant floor heating design software on our website for DIYers to use for free to accomplish a proper design.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
Joe123User is Offline
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29 Sep 2014 07:46 PM
We've just bought the place so don't know how cold the floor can be in the winter, but there was previously a 10-year tenant who with carpeted floors + forced air (prior to demo) said she never had issues with the place being cold. Am getting quotes now for the Rescom radiators as it would be great to avoid the hassle of a new concrete pour and to keep our ceiling height.

Everyone tells me in-floor radiant is the best, but I've lived with forced air or electric radiators my whole life and have never had an issue with temperature in Vancouver... if we did the radiators could get a Nuheat pad for the bathroom for extra comfort, with the rest of the place being laminate, and some tile in the entrance...






PS this is the OP, system had me logged in under different name for some reason
sailawayrbUser is Offline
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30 Sep 2014 10:58 AM
Yes, in-floor radiant is the best heating method by far...at least for comfort!  However, if you start to factor in overall operating efficiency/performance and installed cost/ROI or if you also need AC, it's perhaps not the best HVAC solution.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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