radiant floor heat install questions

[fehren2800]

I am in the process of having a new garage built. I work all day so I see the progress when I come home each day and it has been going pretty well. I am supposed to get the slabs poured on Wednesday so the radiant floor tubes were installed today. Here is what I came home to;



The main area of the garage is 28' x 32' and it has 2 runs of pex, and the back area is 10' x 32' and it has one run of pex. Is this enough heating capacity for the size of the slabs? I haven't checked the elevations yet as it is pouring outside, but the areas right near the overhead doors look awful high.

I'm happy that they ran the pex through rigid tubes where they exit the slab, but I'm not real sure about the rest of it.

My contractor has been doing a good job so far, but this is one of the subs he is using. Looking for advice.

Thanks.

 

[yeldogt]

I like to use more PEX with closer spacing .. and i like to run the PEX so the hotter water is around the permitter.

More tubing allows for lower water temp and more even heat.


How did they calculate the load and tubing needed

 

[SSpanky]

How far apart are the lines? i'm guessing the metal grid is 6"x6".

 

[SSpanky]

I would like to see more runs along the front of the doors, this is where the heat loss is, imo.

 

[fehren2800]

I don't know how they calculated the load. What kind of answer should I be getting to that question?

The spacing is at almost 24". That seems like it is too far. I also thought for a space this large that more than 3 loops would be used. I am guessing each leg is close to 300' long.

 

[brewchief]

What size pex? If you look on the pex it should have footage marks, won't start at zero so there will be some math.

 

[stigedis]

I just put tubing in my 30x40 garage. 4 300 ft loops. Hottest water around perimeter, in front of service and overhead doors at distance of 6". Remainder 12". Did some research and that seems to be standard. 1/2 o2 barrier tubing. If it were mine, I'd make them re-do. Only 1 shot to do it right.....

 

[fehren2800]

It is 5/8 pex. I just checked spacing. smallest spacing is 20" and largest is 24"

They won't be pouring tomorrow as it is calling for rain again, but I think I will let the contractor know that I'm not happy with what is currently installed. I think 12" spacing would be a lot more efficient and would only require 1 more length of tubing. Is 300' too long for each leg?

 

[mygarageone]

12 " is typical for most slabs . I did mine at 9" heats faster and like was mentioned at a lower temp.

 

[rburke65]

Non expert here but it does not appear to me to be enough tubing. And I also wonder how did the calculate the load?

 

[fehren2800]

I basically have a 30x40 space (32' x 38' to be exact) but I have the back 10' x 32" separated from the front by an interior wall with a 6' opening. That makes the spacing a little more difficult, but they should be able to handle it if they know what they are doing. Here are a few more shots of the setup;

 

[TheEquineFencer]

I think I did mine with 1/2 inch pex on 6 inch spacing. max run was less than 320 Ft. A friend of mine did 3/4 pex on 9-12 inch spacing.

 

[yeldogt]

The larger diameter PEX will be able to handle a larger flow ... I have never used anything other then 1/2. The more insulation you have the better it is going to work.

The point with radiant is to install enough tubing to provide a constant temp over the entire floor -- within the design temp water. With more tubing you have more surface transfer from the PEX to the slab and a uniform temp across the slab.

With less tubing you will need to increase the water temp, this increases the hot spots -- can be an issue depending on what is above.

I would not want to be standing directly above one of the tubes running overly hot water.

Even with a system using lots of tubing -- fine tuning the area is a good idea. You would not used a high heat permitter layout and then cover the hottest tubing with floor cabinets or wall closet. I like more zones in a garage.

People do this all the time in Kitchens -- and the lower cabinets get too hot and they put tubes under refrigerators.

 

[anthony666]

fehren .. 5/8ths pex is for snowmelt systems, not slabs .. 5/8ths fittings are hard to find, it's just gonna be an expensive PITA .. it's like those 7 lug trucks ford brought out, just oddball weird **** .. 1/2" pipe

also is that watts 'onyx' pipe ?? again, oddball **** .. if you ever have to do a repair be prepared for a long system down time while someone hunts through a dusty stock room searching for a cobweb covered part

you want a perimeter run 6 inches from the wall on 6 inch center, you concentrate heat there because that's where your heat loss is.. then fill the rest in on 12 inche centers .. that is just a lazy install or the guy only has very basic knowledge .. you only wanna do it once, do it right

 

[Highbeam]

Maybe he had 1000 feet of that oddball onyx **** to get rid of and just "made it work" for your slab. Why else use such an outdated and obsolete pipe.

Pex is cheap, rip that **** out and use that handy 6" grid to lay 1/2 o2 barrier pex, 12" spacing, in loops all about the same length and not exceeding 300 LF.

There is no need for further load caclulations at this time. Get the right pipe in the ground.

 

[fehren2800]

Here is the system design sheet I was given. As I know pretty much nothing about this I will post up a pic of it and hope you guys can clue me in.

 

[UpstateNY]

I just put tubing in my 30x40 garage. 4 300 ft loops. Hottest water around perimeter, in front of service and overhead doors at distance of 6". Remainder 12". Did some research and that seems to be standard. 1/2 o2 barrier tubing. If it were mine, I'd make them re-do. Only 1 shot to do it right.....

Just did mine last year, exact same specs, this is standard, heats very well.

Here's the pex manufacturer he's using, never heard of them until now. You can bet he's getting the stuff cheap. It mihgt be good stuff, I don't know.

http://www.viega.us/xchg/en-us/hs.xsl/index.html

He used their calc tool, get it here: http://www.viega.us/791.htm

Intall it on your pc and run some scenarios, it ain't rocket science. My thought is he "forced" the use of 5/8 pipe. I used a couple of programs to design mine, they all defaulted to 1/2 pex, with the spacing as quoted above.

Their PC program might be putting out a minimalist design i.e, cheapest pipe per ft, minimum amount of pipe (large spacing), quote comes out for less $, happy homeowner/contractior, Viega gets the sale. How the floor performs is another question.

 

[brewchief]

Just did mine last year, exact same specs, this is standard, heats very well.

Here's the pex manufacturer he's using, never heard of them until now. You can bet he's getting the stuff cheap.

http://www.viega.us/xchg/en-us/hs.xsl/index.html

Viega is a huge manufacturer, not low end cheap stuff at all.

 

[Highbeam]

The printout specified 18" spacing. You said you had more.

The printout also specified 74.4 degree surface temp. That's not what you want.

That printout has no way to account for even heating. You could have one really hot pipe in the middle to push the btu but having the 1/2" pipe every 12" is supposed to make the heat even.