Lightweight concrete question

Trapper_Dave

I am needing some help on a project that we started some years ago.
We have a 2 story remodeled farmhouse with 1/2" PEX 8" o.c. on both floors as well as basement.
I have a Buderus boiler (145k) and intending to back it up with an 85k gas boiler. We have a 1000 gallon buffer tank (open to atmosphere) in the basement. We have the basement fired up and currently live in the basement. Now we are hoping to finish upstairs and move up.
A couple of questions:
When the contractor poured the second floor, he used a lightweight mix replacing the gravel with perlite, resulting in a density of around 36 lbs./cu. ft. Now I read in my "Modern Hydronic Heating" book by John Siegenthaler this statement: "Because of its reduced ability to diffuse heat, lightweight concrete with a density less than 110 pounds per cubic foot is generally not suitable for radiant panels."
If I got my calcs right, I need 15.8 BTU/ft2/hr. upstairs. We are hoping to have 3/4" ash flooring upstairs. If I consider that the ash will be about R-1 and the 36 lbs. concrete another R-1. Does that mean I would be at R-2? I thought I read somewhere that once you get around R-2 on the floor, performance drops off pretty quickly?
So, what do I do now? Tear it out and repour. Or just live with it.

Thanks. I am still scrambling to learn this all.

Zman

Never mind...

Trapper_Dave

The way I look at the numbers on your table, they are for 6" walls. So my 1 1/2" concrete should be around R-1.5, right?

hot_rod

I think you may still have a workable system. The RadPad from the RPA site allows you to run some quick calc. http://www.radiantprofessionalsalliance.org/Pages/default.aspx
It's not a substitute for an engineered design, but gets you some ideas.

Would you consider a thinner engineered flooring? That would help some.

Also the furnishings in bedrooms can hamper the output of the radiant floor panel. Any furnishings that go to the floor will limit output to the space, see heat flux page 486 in Modern Hydronic heating 3rd edition.

Even with Perlite there is still some portland in the mix and it will transfer from the tube. Crunch some more numbers, no need to rip anything out, worse case you need some supplemental on design or below days.

Are you positive it was a Perlite mix and not a pea gravel mix?

Zman

Trapper_Dave said:

The way I look at the numbers on your table, they are for 6" walls. So my 1 1/2" concrete should be around R-1.5, right?

Dave, You are correct. I misread the table.
I agree with HR with an output of 15.8, you have a pretty good chance.

Gordy

part of what I see is loss of speed in response time, and maybe some flywheel. Which can be controlled. Tubing being 8" oc is helpful.

Trapper_Dave

Couldn't find the Rad Pad. 100% positive it was Perlite.
The bad thing is the first floor ceiling didn't get insulated because I was feeling poor at the time even though Gordy had advised it to me in an earlier post. Now drywall is up but not mudded.

Gordy

If I remember right weren't your floors out of level? Quite possible the contractor chose the lighter weight mix because of uneven loading. Smart choice actually.

You could always blow insulation in the ceiling your not mudded yet.

Trapper_Dave

Thank you very much for the advice. I am going to take a good hard look at the numbers again.
One other idea I thought of is to simply add a Quick Track over the concrete that is there now. This would make the install of our hardwood floor simpler. Not sure if this sounds like a reasonable direction to pursue. Maybe someone has a thought?

Rich_49

Instead of QuikTrak with 5/16" tubing and higher head losses maybe look at the Sunboard Panels , can use either 3/8 or 1/2 tubing , 8" spacing and transfer layer on top as opposed to the bottom where QTs aluminum is . More responsive and easier to use than QT .

Hopefully the poured floor has some semblance of level to pull off either . Your 3/4" Ash floor has an R value of .8 .

Gordy

Before you get crazy here see how it performs before the flooring goes down. Then you will know if an extra r.83 will kill it. Or not. I think you will be fine with 16 btus a SF load. Your tube is 8" on center.I think I would sacrifice a 3/4 hardwood for a nice 1/2" engineered before I put down another layer of tubing, and add another 5/8 build up to the floor plus weight.

hot_rod

Good advice from Gordy, try the system bare naked before you start adding or modifying. I don't think you are too far off with the installation you have. sometimes you can bump SWT a bit to cover some shortfalls.