I normally do murals and plasterwork bas-relief, custome copper or stonework, etc, but I also do a lot of work for a family with security concerns where the female HO does not allow anyone unknown onto the premises due to fear... so I don't sub any work for them and am often learning something new. Never a complaint when I have to redo, though, good situation for me.

In this case, it's a floor project - 3100sq zone 4C (Portland OR), tight envelope.

HO is requesting endgrain flooring in mosaic throughout.

I suggested an upsell to hydronic while at it.

For this home, 2 story, they have an encapsulated crawl space (no outside ventilation), with R24 polyiso on the foundation walls (plus concrete and earth - 51-53 mean soil temp), with 1" on the exterior (kind of a waste I know), and R15 on the floor under the vaporscrim. I ran 6" polyiso on the rimjoist, as well. There is no insulation on the flooring underside - I vented HVAC system to there to prevent moisture but may need to switch to a dehumidifier for a hydronic changeover. Encapsulating that 30" crawl with 28 supports was the worst job I ever did, never again. Did it to improve their 'air quality'. Nice improvement on their mold tests, omitting the cladiospores from outside.

Their floors are 1.5/8" T&G Fir over 4"x10" at 48"OC. On top of this they want 1" endgrain Hardwood which I'll gluedown (thought I suggest Fir again but with metalcomplex dyes thru WD Woodlock). Material is really not important as any endgrain is incredibly strong, and I'll epoxy/sawdust grout them. Endgrain should also limit width expansion and contraction to a minimum. The metal dyes will make it look like whatever and a solid pallman finish in enough coats will hide open grain vs closed, etc, so I dont see the species mattering.

As they will end up with about 2.5/8" of total wood thickness I figure R3 resistance to the floor surface.

This seems viable to me in this situation to staple up, instead of use an Omega from Thermofin or Blueridge (which seem to be good suppliers from what I've read) topside with plywood sleepers. Downstairs this'd give a lot of floor thickness to manage at doorways, plsterwork mural walls, as they are currently just 3/4" HW flooring over the T&G sub - that's all I've got to work with downstairs unless I want to redo every door and dont want to risk touching into the walls.

I've already done a heatcalc and will use loopcad to plan a layout, so just planning on a Rinnai tankless to supply, 3015 sq ft needs around 40k BTUs to heat.

Upstairs gonna stick with Omega with plywood sleepers as it's a traditional subfloor over 2x12.

So, long story short, do you think stapleup will work in this situation?

Is a heavy gauge Cplate needed from Termofin or will a thin from Blueridge suffice?

Also, I though having someone come in and pour gypcrete would be nice, and change the flooring surface to a handmade tile. But concerned we'd have to set the tubing in at least 1.5" plus final tile, just too tall again.

Anyways, appreciate your thoughts so I don't bungle this for a fantastic client.

No matter how many times I edit that, I can't get spaces in to break up the wall of text. Forum keeps adding them together - sorry!

You can type in "<br>" to get a break. Two for a new paragraph.

I have always added a single space and a / betwen br and the >. Just copying the HTML code i see when I use the quote option to quote someone elses post...

Well, if you are using Avenir HeatCAD and LoopCAD to accomplish this HR design, the software will tell you whether this will work or not and precisely what your water supply temperature will need to be in order to make it work...provided you enter all the required parameters correctly... Under-floor HR is always the worst HR performance option. How bad depends on the ratio of R-value above the PEX versus below the PEX. There is plenty of free software available to quantify precisely how much the monthly/annual heating cost will be with various heating options and performance levels, and only the homeowner can decide if the increased cost of under-floor HR is acceptable or not. Of course, many homeowners don’t bother to understand what is possible and just accept whatever they are told/sold.

Thanks Sailawayrb, I appreciate the information!




There is an R of 3 above, and an R of 0 beneath. Crawl is in the buildings conditioned/sealed envelope & is a 3000 cu/ft space (aprx), that is insulated to about R30 including earth, for zone 4C.

So a staple up would obviously heat the crawl more than the rooms above, but shouldn't that heat then move back up into the occupied envelope?

What I cannot figure out, is if the heat remains in the crawl and radiates down into the earth, and how much loss is that versus how much will rise through the R3 floor instead - it should be 3 but then again, we've got what 30 deg of surface in contact and 330 exposed to R0, so shouldn't that effectively be more than R3 resistance? Or am I overthinking it?

Or how much radiates down into the envelope if I use an on floor method; should be closer to a true value since the pex will be encapsulated in the layer itself instead of simply sitting on it... I get how much an R is, but I don't know how to plan the absorb sink the earth is going to factor since the crawl is sealed, and the exposure of a pipe just sitting there on a surface with minimal contact. Should've been an engineer so I'd have some education on what tools to utilize and the correct approach to thinking it out.

I have included two registers that are open between the crawl and the first floor to ensure the air down there did not stagnate.... so there is some fluidity. But this is a little out of my paygrade.

Ultimately, reading and reading on these forums (amazing advice everyone, thanks so much), it looks like it is better safe than sorry, and do the doors.

Sure thing and glad to see that you fixed/added sentence/paragraph breaks!

I suggested on another recent post that Dan from Blueridge contributed, to respond to your plate question in this post.

Unless the space below the floor is conditioned living space, any downward heat loss is normally considered forever lost. First steps are a proper room-by-room heat loss analysis and than a proper HR system design.

I would suggest visiting a library and getting a copy of "Modern Hydronic Heating" by John Siegenthaler, PE to better understand this subject.

Here are some graphs you can use.

13 btu/sqft with R3 above and double thin plates - looks like about 145F, which is OK.

http://www.uponorpro.com/~/media/extranet/files/cdam/cdam_manual_7thed_0711_appe.ashx?version=072920111126

Even though the crawlspace insulation might be considered under-plate insulation (with a very large air gap), I'd put some additional insulation under the plates.

Well, those charts certainly illustrate the stark supply temperature performance difference between concrete slab and under-floor emitters... For 20 Btu/SF, zero finished floor R-value (i.e., no carpet or hardwood on top of basic emitter), and 20F delta T:

9” spacing in 4” Concrete Slab: 87F

8” spacing Under-Floor without Plates: 154F

8” spacing Under-Floor with Plates: 138F

Of course, all these numbers get worse if the more typical 12” PEX spacing is used. The 4” Concrete Slab becomes 90F, but there isn’t a chart for Under-Floor at this 12” spacing. And the numbers get even worse if you have finished floor R-value (i.e., carpet or hardwood on top of basic emitter).

Note that these charts assume "negligible downward loss in accordance with good insulation practices”. That means you must have way more R-value below the PEX than above the PEX. The other thing that is notable is how the Joist Trak system performs significantly better than the other Under-Floor options, about 110F for same scenario.

And finally, if you need significantly more than 20 Btu/SF and use the other Under-Floor options, you quickly go off the recommended usage area of chart. Using Under-Floor with Plates at 13 Btu/SF and a finished floor R-value of 3, you are indeed looking at about 145F...assuming you satisfy "good insulation practices".

A couple more data points relating to underfloor vs slab performance (20 btu/sqf, 20F delta T, R3 covering):

12" spacing in 4" slab: 150F

8" spacing, Joist Trak: 150F

No difference! Difference comes mostly from reducing the R value above the emitter. Under floor adds more R value than slab or above floor.

Well, the other difference is the significantly increased cost of having to purchase/install plates and additional PEX...

More importantly, Siegenthaler and other reputable HR designers consider floor finishing R-values greater than R2 to be fully blocked and don’t consider that floor area as providing adequate heating capability. I also can’t imagine someone putting R3 floor finishing over an efficient concrete slab emitter so as to require going from 90F supply temperature to 150F. Once you start bumping 140F, it’s really time to consider doing something other than HR floor heating...