I am pouring 4-5 inch concrete main floor over steel and placing 3/4 inch pex
tubing for radiant heating system. what is the preferred spacing of layout?
6 inch, 8 inch, 10 inch???
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It depends. What does your heat loss analysis tell you?
There is no heat loss analysis. It should be quite low.
If the heat loss is so low, then why are you doing in-slab hydronic at all, and with three-quarter-inch PEX.
What is the heat source? Is the slab heat the primary heat? Are you even in a heating climate? What will be the floor finish? At least a little more infomation is necessary for us to give an educated guess.
I am in a deep freeze climate, where a "design temperature" of -30F is used to calculate heat loss. We heat with in-slab radiant, as the primary and only means of heating. Heat loss and exposure determine tubing spacing.
But I have been in resorts in the Caribbean where in-slab radiant heat is used just to boost the comfort of bathrooms and dressing areas, places where you are likely to be barefoot. That is a completely different use of radiant, and an entirely different design is used.
See why we need more detail?
First, good luck getting any of those on centers with 3/4" pex. The only time pex that large is needed is if you are heating a very large area and it's the only way to do more than go "down and back" more than once and keep your frictional loss down.
If this is residential, maximum on center is 12" or you'll get heat stripes on the floor surface. Tighter on centers might be required for high R floor coverings or high load areas.
A heat load calculation should definitely be done though.
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I live in western NC, Asheville. Outside temp may get in teens in winter.
Two floors. Basement
Main floor
Both 4-5 inches concrete. Basement insulated with 2 inches blue styrofoam.
I was told by one heating contractor six inches between tubing preferred. That seems overdone in my opinion.
Thanks for your help.
Rosey - I live in a similar climate. It really matters how well your house is insulated. I have 8 in spacing in the basement slab - this readily heats the whole house, but mine is super insulated. Pex is pretty cheap, and it would be better to use too much than too little.
The temperature of the water you will be pumping through the tubing matters too. I would go with your heating contractors recommendations unless you have reasons to doubt, in which case I would find another!
Treat every person you meet like you will know them the rest of your life - you just might!
still no way to tell without a load calc. one room may have a lot of glass and carpet, one may have neither. On center requirements can vary from room to room.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks for your help
I am having my heating contact figure the load equation. My house will be very insulated- total cement blocks with inside furring, rocks and stucco outside.
In searching around, I discovered that Radiantec will do a layout drawing from my plans and give me a quote for 7 cents per foot, or about $400. I may do that.
Another question: Does anyone have an opinion about whether there is pex tubing equal to or better than (Wirsbo) Uponor. they have a 25 year guarantee.
Rosey - I thought Radiantec was free - but why bother with them if you have a heating contractor?
Treat every person you meet like you will know them the rest of your life - you just might!
Doesn't sound from what she has said that her contractor, whoever he or she is, knows anything at all about radiant, nor has any resources for it.
Doesn't surprise me. She's in a region where there is little to no heating done with hot water, and forced air HVAC is used in everything, with gas-fired furnaces for the heating side, and a lot of electric heat pump usage.
You pay a really big premium in her climate to heat with radiant, then cool with some other means.
Hey - I am in an area like that!
Its rare to find a newer house here not vinyl sided with a heat pump. So much for fine homebuilding. But the older stone homes are beautiful.
I have built two of the three radiant heated houses I am even aware of.
As for me, ICFs and Radiant = awesome house.
Treat every person you meet like you will know them the rest of your life - you just might!
You must be cooling somehow, right? Are you blowing your cooled air through ducts?
But you are heating with radiant? What are you doing to heat your water?
Gene -
I cooled last summer with a window unit. We have ICFs and an open floorplan, so it covered the entire house pretty readily - no trouble keeping up. 1720 interior s.f. per floor (outside its 1920 s.f. - ICFs eat floorspace) with a full conditioned basement.
It was a little loud, though, (and ugly) so we are looking into a mini-split, centrally located. My HVAC guy will be selling me the equipment. He was a little shocked to hear a window unit covered the entire house.
We are using an oil fired Bock water heater for HW and radiant. So yes, we are paying twice for heating, but my kids like to lay on the concrete floors, they are so "cozy".
btw - I always enjoy your posts - thanks for all the thoughtful comments
Treat every person you meet like you will know them the rest of your life - you just might!
[Doesn't sound from what she has said that her contractor, whoever he or she is, knows anything at all about radiant, nor has any resources for it.
Doesn't surprise me. She's in a region where there is little to no heating done with hot water, and forced air HVAC is used in everything, with gas-fired furnaces for the heating side, and a lot of electric heat pump usage.
You pay a really big premium in her climate to heat with radiant, then cool with some other means.]
Rosey is not a she. And at 3500 ft elevation, air conditioning might help for two months out of the year. We're not part of the warm and fuzzy crowd.
Not true about little or no heating done with hot water. It's people like me who will promote the concept. But we're not the pioneers here.
I haven't decided on the heating contractor engineer yet. One is doing his calcs, and a wirsbo contractor is 15 miles away in Arden. I will let you know.
Does anyone have an opinion about the BEST pex?
Yes, and here is my opinion. Use Uponor (Wirsbo).
I think you are putting the cart before the horse, Rosey. If responsible hydronic heating contractors can be found in your area, then find a good one or two and let them assess your situation and make proposals.
If you are really technically inclined, download the free heat loss analysis package from SlantFin (Google and you will find) and do your own heat loss, then do some more work on radiant slabs and find out what kinds of spacings using what diameters of tubing at what input temps generate what kinds of Btu/h emittance. You'll get there, it'll just take a little work.
Did I ask you already about this? I can't remember. What are you planning as the device for heating the water?
Please don't say a hot water tank.
Here's an idea. Go over to HeatingHelp.com's "The Wall" forum and read a few hundred of the posts that might relate to your situation. It's all about hydronic heating over there, and populated by pros. I've found out that tech questions such as yours are not best addressed here at Breaktime.
Actually Gene I did heat my entire house using a hot water heater. It was a 3 zone, 4 loop, 3 thermostat Wirsbo system, baseboard hot water radiators. I lived further north than you and was with a 1/4 mile of one of the great lakes (COLD).
I used it for 3 winters and was the best heating system I ever had. And cheapest. Mind you I could get free any hot water tank (used) any time I needed one. I figured that the total system had only about 5 gallons of water in it. When I did it I really wasn't sure it would work but friend of mine who always comes up with workable, wierd systems said it would work and it did. He always said that boilers were too expensive and complicated for such a basic need like pumping it through rads.
I don't think I would do it for a customer but the wife keeps trying to get me to do it in our present house.
roger
Thanks Roger, Mister T, Gene, Rob, Brian.
Have checked Heating Help. I would never have found that myself.
It looks like no one has an opinion about a pex manufacturer
that can beat Uponor.
Edited 4/8/2007 5:42 pm ET by Rosey
Edited 4/8/2007 5:43 pm ET by Rosey
Make sure whatever tubing you use has an o2 barrier, and do not use the large diameter pipe. I would also STRONGLY recomend that you make sure any major rooms are isolatable on their own loops. Otherwise you have no ability to adjust output later on should one room end up a little cooler than another.Also, for a high mass system in your climate, you're going to want slab sensors in addition to thermostats, and you'll want a good thermostat at least, not just a standard round. I recommend a Tekmar 508 with an 079 slab sensor as a bare minimum for controls, using water temperature that is appropriate for your system.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
6" is probably an arbitrary standard back from the days of tying the tubing to re-mesh.listen to rob3/4 sounds to big to bendI don't Know what I am doing
But
I am VERY good at it!!
In concrete slabs all I've seen over the years and all we use is 1/2" pex 12" oc. when used in a well insulated shell.
As for brands, they are becoming close to a commodity with very little difference between brands for straight PEX.
Beer was created so carpenters wouldn't rule the world.