I am going to be pouring a slab in my basement in the next few weeks and don’t have any specific plans for the basement’s use as of yet. It is 26ft by 43ft and I am thinking I should consider putting some tubing in the slab to give the option of running radiant heat in the future.
I have a few questions and wonder if there is a book or other information source that could give me a brief overview of the basic theories and do’s and dont’s.
My questions so far include:
Can I effectively heat a slab that size with one loop of tubing?
How many linear ft of tubing should I place in a slab that size?
Is there a pattern one should follow when laying the tubing
Is one brand of PEX preferable?
What type of insulation is appropriate under the slab?
I am on the central coast of California. Winters are mild and I am mainly looking for a means of taking the chill off the basement, not trying to make it toasty warm.
I am leaning towards a mat of #3 rebar rather than welded wire mesh.
I have a huge supply of firewood so I am intrigued by the prospect of a wood fired boiler but realistically gas fired might be a lot simpler.
Thanks for any suggestions,
Karl
Replies
Karl, As one starting point for information check out http://www.radiantec.com.
There is info available from them for sizing and layout.
Edited 7/17/2007 5:24 am ET by OldGuy
Old guy,
Thanks for the link. I downloaded the installation manual and tubing layout manual.Karl
Tubing spacing is figured by heat load.. if this is a basement (basement in CA?) your load is probably low and I'd do 12" o.c. maximum to avoid heat striping. max loop length is also determined by heat load, so it's pretty important, but you can keep yourself out of trouble by keeping loops to 250' or less with 1/2" pipe.Don't waste your money on tubing any larger than 1/2".use an oxygen barrier PEX or a PEX-AL-PEX so you keep your heat source options open.Make sure you can shut off loops if you need to.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
"Can I effectively heat a slab that size with one loop of tubing?"
No. You will be limited to a max length per loop of somewhere around 250' - 300'. These can all be on one heating zone, with the loops all going to a manifold to tie them together.
"How many linear ft of tubing should I place in a slab that size?"
Generally, run the tubing with about 1' spacing. However this, together with the size of the tubing required, is something that should be calculated by your supplier based on heat loss.
"Is there a pattern one should follow when laying the tubing?"
Yes. A common pattern is to run tubing around the perimeter first (hotter water to the coldest spots) and then run a back & forth grid over the remainder of the floor and back to the return manifold. Make sure to avoid running tubing in areas where you will later be installing anything that requires a floor penetration by nails, screws, drills, etc. Also keep the tubing away from toilets with wax rings -- they'll soften and melt. Takes a bit of planning to do this right. Kind of like those brain teasers where you have to draw a figure without crossing lines or lifting the pencil off the paper. ;-)
"Is one brand of PEX preferable?"
I like Wirsbo, but that's mainly because the local supplier I use is great - very knowledgable and helpful. I also like the fitting system that uses the expander vs. the clamps.
"What type of insulation is appropriate under the slab?"
Extruded foamboard on leveled & compacted crushed stone. I use 3" of foam, but 2" is probably fine. I like to put the tubing on the foam and staple it down. Others like to tie the tubing to the rebar grid to get it more centered in the slab. The latter is said to be just a bit more efficient. The former is quick, easy and (I think) less likely to damage tubing.
Wirsbo has some very helpful literature you might want to pick up.
"I have a huge supply of firewood so I am intrigued by the prospect of a wood fired boiler but realistically gas fired might be a lot simpler."
This could work, but would probably require a whole-house plan -- probably wouldn't be very efficient or effective for just "taking the chill off" a basement slab - something with a pretty intermittant demand.
Mike Hennessy
Pittsburgh, PA
Mike, Thank you for the detailed reply. You cleared up a lot of uncertainty.Karl
Get ahold of the radiant heating "bible": Modern Hydronic Heating by John Siegenthaler. If you are serious about hydronic heating this is the text to get if you only buy one book. I know, I have gotten numerous other books. Also check out the wall at heatinghelp.com.
Would you recommend the book if I am only doing a simple basement slab with four loops in it. I ordered tubing and misc parts from NRTRob and downloaded Radiantech's installation manuals.I get the impression my application is pretty simple but if buying the book for a hundred bucks will help me do a better job I am not opposed to spending the money. In this case I don't plan to become any sort of expert on the topic I just want to have the option of a warm basement down the road so I am going to put the tubing in prior to pouring the slab.Thanks, Karl
here is the link to a pdf of the Wirsbo manual.
It is in the library over at the Wall.
http://www.heatinghelp.com/pdfs/71.pdf
I think Ipex is there too.
What, you don't have to buy the book?? :)
That book is useful later, if you want to be fully educated on hydronic heating. For now, you don't need it.It is definitely the "bible" of modern hydronics though. Years and years into this, we still refer to it almost daily. Anyone who wants to get serious about learning about hot water should get it, when they are ready to get serious.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Karl,
I appreciate your qualms about the cost of the book, exactly how I felt about it. See if you can look at the book somewhere (Builder's Booksource in Berkeley has it.) The first book I got was Dan Holohan's Hydronic Radiant Heating ($25). I recommend it, it's a good introduction. He refers to Siegenthaler's text which I didn't get it because of the =$100 cost. After I got it I realized what a good resource it is for materials and methods, and it enabled me to ask intelligent questions and understand the answers. If you are in the construction business like I am, you know you can't know everything but you make a point of having resource material available to point you in the right direction. My only gripe is that he doesn't have a reference/source list, but that is my academic bias. Pex will cost you more than 60 cents a foot, this book will set you back some 10 cents a sf. By the way, on page 76 he covers wood fired boilers. Good luck!
Sawduster, You make some good points in favor of buying the book. Maybe I will buy it after all.Thanks,
karl