Hi everyone CLICK HERE FOR PIC Central Ontario build on piers (don't ask)... Client hopes to use a large on demand electric water heater to heat both potable and infloor heating system. It will be used as a backup heat source, wood pellet being the primary source. Can anyone see any problems with this system? Will the wide plank pine handle the heat? Will most of the heat radiate up or go down and outside? Should we consider a reflective barrier of some sort? Bury everything under loose fill, or leave an air gap between loose fill and pex? Thanks in advance. Tom

Consider that rigid foam is useful to reduce thermal bridging (and localized high RH) and that the exterior isn't the recommended place for a vapor barrier. Consider taped sheathing (no exterior film, possibly Zip) as an air only barrier instead.

Aluminum plates increase the heat output from hydronic tubes. In any case, don't let insulation (cellulose) touch the heat emitter.

On a more speculative note, consider non T&G pine that would allow a little bit of convective air flow through the floor (would make a big difference).

Much of what you ask can't be answered well without knowing the heat load/btu rate.

Posted By tbomb on 01 Nov 2013 11:55 AM
Hi everyone CLICK HERE FOR PIC Central Ontario build on piers (don't ask)... Client hopes to use a large on demand electric water heater to heat both potable and infloor heating system. It will be used as a backup heat source, wood pellet being the primary source. Can anyone see any problems with this system? Will the wide plank pine handle the heat? Will most of the heat radiate up or go down and outside? Should we consider a reflective barrier of some sort? Bury everything under loose fill, or leave an air gap between loose fill and pex? Thanks in advance. Tom

To start with in central Ontario putting an exterior side vapor barrier under the insulation with an air-leaky flooring type guarantees that the bottoms of the I-joists (and the insulation) will take on copious amounts of moisture in the winter, and you'll have a mold issue in short years, and a potential rot issue in the decades ahead.

On demand hot water heaters are not designed for the types of flows required for heating systems, and may not deliver sufficient water temperatures necessary for mid-winter heating in central ON (especially without heat transfer plates of any type.) If it's connected to the potable water there are also stagnation/pathogen growth issues to be attended to, and you must use bronze or stainless impeller pumps.

Reflective barriers do next to nothing at the delta-Ts you're likely to be seeing, unless you're running the PEX at it's full rated max temp, where it does at least something.

Provided you fix the water safety & pump issues, eliminate the bottom side vapor barrier, put a foil or (easier to deal with, since you don't have a sub floor) aluminized-polyester vapor barrier (sold as radiant barrier, but read the ASTM E 96 vapor permeance carefully- it MUST be well under 1 perm, hopefully under 0.1 perms) between the I-joists & T & G, and plate the PEX to the T & G (either sheet metal or extruded), then blow the joists chock full of cellulose at least 3.5lbs density (dense-packed for air tightness and low settling.)  Then you'll have at least a chance of meeting the design condition load (as yet uncalculated or unstated.)  The vapor barrier will be your primary air barrier, so overlap and seal the seams with fiber-reinforced duct mastic to limit air leakage into the cavities to avoid rotting out the I-joists and half inch ply. Since there WILL be seasonal dimension changes on the pine gluing isn't going to cut it, but an aluminized polyester vapor barrier would also serve as a slip-surface. (Rosin or kraft papers are the traditional flooring slip surface, but nowhere near vapor retardent enough in this application.)

Pine can take the heat without any issues if you're running it at 50-60C domestic water temperatures out of the tankless. If you need 60C or hotter water to stay warm, it needs to have a tempering valve on the potable side to limit the temp at the taps to something 50C or less.  The typical rated operating limit for PEX is about 80C (though it can even take 90C for quite awhile before it sees much degradation.)

okay, thank you. The vapor barrier issue wasn't a surprise....

UPDATED PIC

We are trying to limit the need for a third fuel (wood/electric/propane). Client insists on wood or wood pellet as a primary source, and with electricity already in place we figured we could use a large on demand electric heater. I thought for sure this would exist, but perhaps a propane boiler is the only option.

Keeping the potable water separate can be managed.

I updated the drawing .... I have the radiant barrier running underneath the hydronic tubes. The problem I see here is that all the plumbing, and in floor heating lines (and some electrical) all puncture the vapor barrier.... We are really hoping to do everything from the inside, putting the floor down last.

Thanks again
tom

How much resistance to heat conduction is that Pine T&G going to offer when all you've got down below is AIR to get the heat from the PEX to the floor assembly?

ICFHybrid, so you are saying the hot air will just sit there and not conduct up towards the living space readily?

If you are locked into this assembly approach, abandon the hydronic radiant floor heating plan completely. At best, it will be extremely inefficient and costly to operate. At worst, it will be totally inadequate unless you are just looking to keep the floor less cold. I would speculate that worst is more likely than best, but you can run the numbers using the software on our website to convince yourself. Place the vapor barrier in top of assembly just below the flooring and provide ventilation in bottom of assembly to ensure adequate drying capability.

okay thank you

The client is just paranoid about cold floors, but insists on building on piers....i told him you can buy slippers for 3 dollars, he didn't like that... anyone have success keeping the floor warm-ish on piers with no 'curtain' walls?

thanks guys very grateful

Air is a poor conductor of heat. Worse yet, that heated air can easily escape.

> client is just paranoid about cold floors

If it's not a backup heat source and you just want to raise the floor temp slightly above (vs below) the room temp, then it will be fine without plates.

tbomb - your pic does not show the beams over the piers. Consider leaving the vapour barrier where you had it and installing a joist system between the beams to hold the insulation. In effect, two floor systems. You might add some insulation to the main system but the most of it should be in the lower system.

Please explain to the client that there is nothing to stop RATS from entering this house!!

I know you said not to ask but just got to know why piers??

Posted By tbomb on 01 Nov 2013 05:21 PM
okay, thank you. The vapor barrier issue wasn't a surprise....

UPDATED PIC

We are trying to limit the need for a third fuel (wood/electric/propane). Client insists on wood or wood pellet as a primary source, and with electricity already in place we figured we could use a large on demand electric heater. I thought for sure this would exist, but perhaps a propane boiler is the only option.

Keeping the potable water separate can be managed.

I updated the drawing .... I have the radiant barrier running underneath the hydronic tubes. The problem I see here is that all the plumbing, and in floor heating lines (and some electrical) all puncture the vapor barrier.... We are really hoping to do everything from the inside, putting the floor down last.

Thanks again
tom

A vapor barrier with a bunch of holes punched in it where the PEX goes through it can't be detailed as an AIR barrier.  And at air leakage points you'll have even massive condensation issues in winter.   You get less overall air leakage if you put the vapor barrier up against the bottom of the 2" t&g flooring, and ABOVE PEX, only penetrating the vapor barrier in a couple of places (and you can try to air-seal those penetrations with flexible foam of sufficient heat tolerance.)

As stated previously the fact that it's a radiant barrier is moot unless you run the PEX near it's max operating temperature, and even if you did, it may not be enough heat fllux into the floor to meet the design condition load. Using extruded or firmly gripping sheet metal heat spreaders to get the heat out of the PEX and into the floor is a much more reliable method, and it will reduce the water temp requirements.



Yes, the fastener for the plates and the flooring will put hole in the vapor barrier, but the amount of leakage through a nail or screw hole is tiny compared to what you'd see with holes for the PEX.

With the PEX and plates tight to the flooring, you can fill the cavity full with cellulose, to block any lateral air leakage that might otherwise run through that cavity, and add a bit more R between the (now cooler==less lossy) PEX and the great outdoors.


An electric boiler is cheaper than a propane boiler, and in central Ontario may even be cheaper to run, depending on your all-in delivered propane & electricity pricing:


Unlike an on-demand hot water heater, theses things are designed for high temp and higher flow, and constant use. They aren't very expensive as hardware goes either, but like any other heating equipment you have to size it correctly for the load.

By the time you've designed & installed it with sufficient heat spreader plates to be able to meet the load with water temps that don't melt the PEX it would probably be cheaper (and certainly more efficient) to install a cold-climate ductless mini-split heat pump.  At central Ontario mid-winter temps it comes down to just a couple of model lines, the Fujitsu Halcyon XLTH series, or the Mitsubishi H2i Hyper Heating series.  They both have specified output ratings at -25C outdoor temps, and both still run at temps below that.   The Mitsubishi  H2i will stop when it hits -28C to self-protect, but re-starts automatically when temps rise a degree or so.  As I  understand the XLTH keeps on going, at some unrated output & efficiency. If the temps in that location drop below -28C regularly the Fujitsu is the better choice, but if not, the Mitsubishi H2i series has a longer and generally good track record.  The XLTH series was only released last year, but it's based on the very efficient and much-used Halcyon series, with several design changes to avoid problems during extended use at temps lower than -20C.

Ductless heat pumps are pretty comfortable, but not as cushy as radiant floors.  But since the radiant floor idea is just the backup to the wood-burner, it's a good choice. Since these thing modulate, with a 3:1 or better turn down ratio they "play nice" as backup for wood burners, picking up the slack as the fire dies down, then throttling back when the wood stove is re-stoked, with very even room temperatures as it cycles on.  With radiant under 2x flooring there's a bit of a time lag on startup, but if you keep it up to temp it's possible to maintain steady room temps.  If used in combination with a wood stove that lag leads to temperature under/overshoot conditions.

If you scrap the radiant floor concept you can use EPDM sheeting as your vapor barrier.  Poly is too likely to degrade over time in floor applications due to the flexing, compression and abrasion, whereas EPDM  (a common membrane roofing material in commercial construction) is a lot tougher.

Posted By FBBP on 01 Nov 2013 10:19 PM
tbomb - your pic does not show the beams over the piers. Consider leaving the vapour barrier where you had it and installing a joist system between the beams to hold the insulation. In effect, two floor systems. You might add some insulation to the main system but the most of it should be in the lower system.

Please explain to the client that there is nothing to stop RATS from entering this house!!

I know you said not to ask but just got to know why piers??

In a cold climate you absolutely CAN'T put a vapor barrier as the last exterior layer before the sheathing, unless you put sufficient R value on the exterior side of the sheathing to keep the vapor barrier above the ~+4C interior air dew point, which in central Ontario is nearly half the total R-value (!).  That's why Canada's building codes require low-permeance layers to be on the interior side of the assembly.   Even in the comparatively tropical southern edge of central Ontario, (Sudbury, say) the mean daily outdoor temps are below +4C from about the first of October to half-past May, which is more than half of the year.

You need air-barriers on both sides of the assembly and the joist bays need to be air sealed at the band joists and completely full of high-density fiber insulation to get the full performance out of the insulation. But the water vapor permeance of the interior side needs to be orders of magnitude lower than the exterior side to avoid loading the materials in the joist bay with moisture over the long cool stretches.

Like this

Posted By FBBP on 05 Nov 2013 06:59 PM
Like this

Putting all the insulation outside the vapor barrier (and detailing it as an air barrier) definitely works.  (I needed the pic to parse your meaning.)

But relying on just 2x8 cavity fill insulation would be a bit thin in that climate, no?

We still don't have heat load numbers for the house, which is a critical first-order piece of information necessary for designing the radiant floor (or any other heating system.)  The notion that you're going to just dangle some PEX in the cavities, run it at the 80-85C max temp for PEX and it'll somehow heat the house adequately through the ~R2 flooring seems a bit optimistic, unless it's a very high-R (and very air-tight) house.  An I=B=R type spreadsheet type heat load analysis would tell if it's even remotely possible without heat spreaders.  To do that we'd have to know the construction & insulation type/thickness to work up U-factors for the wall/ceiling/floor surface areas, and the area & published U-factors of the windows & doors.

Wow so many smarter people than me out there...

Anyways here comes the bomb drop.... Log home. Large pine logs running horizontal. Chinked with a traditional mortal mix. Many people have built with the identical wall style and say it is a very easy home to heat (thermal mass I suppose). Very few windows and doors compared to today's standards. He is not sure yet on roof structure. SIPS, Rigid foam built up system, fiberglass, blown in cellulose, has all been mentioned for the roof. 2 storey, VERY OPEN CONCEPT, only bathroom and closets will be completely closed off.

This updated pic solves a few problems I suppose. I am really hoping I can install the 1/2" ply from the bottom up then do everything else from topside down. Which means hydronic tubes would need to be secure before the 2X flooring is installed. Anyways, this should spawn some more thoughts/ideas for everyone. Thank you greatly.

CLICK HERE UPDATED FOR PIC

Think about this option, You want to keep your heat in the inside of the building envelope. You are almost there with your latest drawn version.
Have a look at our RHT floor panel system. Others make similar products. It is an easy site install, top down,not bottom up. With this approach you are proper on keeping the heat in the building, not pushing heat through the sub-floor system.
Link http://www.blueridgecompany.com/radiant/hydronic/527/rht-floor-panel-system
Good luck,
Dan

Large pine logs running horizontal. Chinked with a traditional mortal mix. Many people have built with the identical wall style and say it is a very easy home to heat (thermal mass I suppose).

One of the worst possible homes to heat. Logs move and "traditional mortar" isn't known for it's flexibility.

I don't understand why the client seems determined not to have plywood subflooring. Is there a sale on pine 2X?

Yes, companies of questionable integrity will often successfully push their expensive, high profit margin products that they sell like RHT heat plate systems to clients that do NOT bother do a HVAC return-on-investment (ROI) analysis or simply have lots of money to waste.

Exactly right ICF, a log cabin with 2X floor is not a good candidate for hydronic radiant floor heating. However, all the lost floor heat might keep any pipe installed in the floor assembly from freezing and perhaps also keep the dew point within the assembly high enough so as to help mitigate any assembly moisture problem that may require it to be replaced in several years.

Once again Borst hijacks the opinion poll with his narrow minded view on simple street hawkers such as myself, it is a wonder I do not charge myself for my breakfast toast.....
Floor panel systems Warm board, upinor, roth, rehau, stadler panel, and a host of others must all be in the same scam, low tempature delivery systems held with in the building envelopre are more fuel efficent. Finish floor systems can be applied on top, delivered water temperatures can be brought in to the 100 degree range, minimizing the expansion contraction placed on a floor system that is seeing temps in the 130+ range to push through a thick sub+finish floor system.
Our RHT system runs about $3.00 a square foot for all materials pipe, manifold, turns, heat plates, and site purchased 3/4 ply at about $25.00 per 4x8 sheet. Then you have labor. What the other systems cost Warm board, upinor, roth, rehau, stadler panel ... not sure, don't care.
If you have ever climbed up a ladder 85 times an hour to do a staple up, of crawled under an house weaving pipe for days in a crawl space you might consider the idea that placing the heat in the building envelope, using a top down manor is preferable, that any added cost on materials in reasonable given the savings on labor.
All part of the ROI.
Again good luck to all in these unusual times.
Dan