Hi,
I’m real new to this, or any forum, this is my 1st.
My long term plan is to replace my forced air system w/ radiant heating.
I live in a cold climate, AC Isn’t a big deal here, maybe 20% of houses have it.
Anyway, my basement ceiling is only 7′ high. Currently, it has heating ducts taking up about 1′ of that, right down the center of the basement, Stupid.
There are already 3 bedrooms and a family room downstairs.
My idea is to tear out the ceilings, about 800Sq.Ft., and put in tubing.
But downstairs, I’m stuck w/ the floor as is, I prefer radiant to radiators, so I plan to put tubing in the lower part of some interior walls. And build a radiant wall.
I’m even thinking of boxing in the bottom 2 ft. or so and filling around the tube w/ pea gravel for thermal mass and better heat transfer. Still can’t decide if this is genius, or taking a simple idea and complicating it beyound all recognition.
Any opinions on a radiant wall as opposed to a radiant floor?
Oh yeah, I intend to put in a manifold w/ 1 loop this year heated by a gas water heater, it has an exchanger, and test out one wall.
Thanks much.
Bill
Replies
Bill,
It can be done, and it is, though it's not nearly as common a RFH.
There are advantages to RWH...first, if the floor is inaccessible, like a slab, as in your case...the walls can be made to work. Also, if the floor covering is not conducive to RFH...say, a thick carpet pad and plush carpeting. Or, the heat loss from the room is so great that the floors alone can't handle the heating load. You can throw heat in the walls to make the design work. Add in the insulative value of oriental-type area rugs, where they may cause harwood flooring to overheat due to the heat retnetion of the area rug.
The upside is you can get more heat out of a wall than you can get out of the floor. Typically with a floor you're limited by the hardwood flooring to say, 100-115 degrees or so. Or you may be limited due to comfort factors, where you don't want the floor to actually feel too warm. Most walls are gypsum or plaster, neither is limited by temperature, both are temperature-stable. As a result, you can get up to...I'd say...about 70 BTU/foot of wall. With all else being equal, you can heat a generic room with about half as much square footage of wall heat as you'd need square footage of floor heat.
How to do it? Insulation, Al plates, and PEX. You can either use the pre-manufactured sheetgoods that have pre-routed grooves and an Al face already installed. Cha-ching!
More commonly, and more economical, is to take the wall from the floor up to about 4' (or less) down to the studs. Stuff FG batts in the the stud cavitites. Then, you can run 1/2 foil-faced polyisocyanate insulation horizontally, from the floor up to the 48" (or less) line, on the studs. Now run 1.5" wide furring strips horizontally, about 16" oc, screwed through the first layer of half-inch polyiso and into the studs. This will leave you with about 14.5" between furring strips. You'll run two horizontal runs of half-inch PEX and more polyiso between each pair of horizontally running furring strips.
Now rip more sheets of half-inch foil-faced polyiso into 3.25" wide pieces and 7" wide pieces. You'll need twice as many of the narrower strips as the wider.
Confused yet? It gets better.
In between each pair of horizontally running furring strips, you'll have, from the bottom up, running horizontally: a 3.25" strip of polyiso, then a half-inch run of PEX set in a 6" wide Al plate, then a 7" wide strip of polyiso, then another half-inch run of PEX set in an Al plate, then another 3.25" strip of polyiso.
So, from centerline-to-centerline of the furring strips, from bottom to top: 3/4" furring, 3.25" polyiso, 1/2" pex w Al plate, 7" polyiso, 1/2" polyiso w Al plate, 3.25" polyiso, 3/4" furring. Total of 16".
Still with me?
The Al plates? You've seen them. the "U" portion gets tucked into the half-inch gap between the 3.25' and 7" strips of polyiso. The flanges of the Al plates sit on the face fo the polyiso. For you best installation, use adhesive to bond the Al plate to the foil face of the polyiso. That'll stop plate noises. However, bond only one flange, then insert the PEX, then bond the other flange. If you bond both flanges from the start, it may be tough snapping the PEX into the "U" channel in the Al plate.
At the end of each horizontal run, route or cut a groove in the polyiso to loop the tubing back vertically for the next horizontal run.
When done, cover with drywall, screwed into the furring strips.
This will leave you with the lower section of the wall "fatter" than the upper. You can trim the top with a cap rail of some sort, or...
Back when you first stripped the wall, strip the entire wall to the studs. Then run the polyiso/Al/PEX mess up to the appropriate height. Again, for example, 48". Now furr out the studs from the 48" mark to the ceiling so the faces of the furring strips on the upper part of the studs are aligned with the face of the polyiso/Al/PEX sammich on the lower part of the wall. Now run drywall and it will all be in plane.
Realize you'll have to adjust electrical boxes as required.
I'll try to post a drawing later on. RWH isn't that common, so it may be the case where a picture is worth a helluva lot more than a thousand muddles words.
Oy.
Edited to add pic (I hope). Well...looks like I don't have the option of adding a pic when editing. I'll add another post.
Edited 9/27/2002 1:17:04 AM ET by Mongo
Replying to myself again...hope this pic works...
Wow, Thanks for the great response.
If I was looking to heat just one side of a room, this would be fabulous.
I agree w/ your idea, that describing it is impossible, So I drew a picture. (I'm a computer draftsman).
This just shows the bottom 4 ft. of the wall. The idea is to use the gravel, or maybe sand, to transfer and store heat to the rooms on both sides of this wall. As well as help support the tubing. Suppose I could even use concrete, but that'd be much more work & weight.
My basement has a very stable temperature, so I think stability and thermal mass beat out response time for me.
I'm going to send this, then do another message & attach the picture.
Last time I tried it locked up. Don't wish to type this 3 times.
http://www.radiantdesigninstitute.com/page2.htmlbobl Volo Non Voleo Joe's cheat sheet
Doh!
Coulda saved a lot of chicken scratching had I seen that link last night!<g>
Thought your explination was good
provided link AFTER your post for possible additional info. (this site tain't about getting urls but people who provide advice)
Wanted to put RH in our kitchen but too small a floor area, would have to use walls and ceiling too. for enough BTUs
bobl Volo Non Voleo Joe's cheat sheet
Edited 9/27/2002 7:01:35 PM ET by bobl
If this is an interior partition wall, you've got it easy.
Simply run the half-inch PEX as if it were romex. Drill a series of 3/4" diameter holes at heights you choose, about every 8-12" vertically. Snake the tubing left, then right, yadda, yadda, until you end up with a serpentine "S" run of tubing.
For one room you might only need the tubing to run from about 8" off the floor to about 48" high...six or seven runs of tubing. Since this single run will be supplying heat to two rooms from one wall, and if this will be the only wall supplying heat, you can run the tubing higher, even full height if required. It all comes down to the numbers the heat-loss calcs spit out.
While tubing droop in a 16" stud bay is nothing you have to worry about, you don't want the expansion/contraction cycles to cause the tubing to "walk" along the studs. So you'll want to secure it here and there to prevent lateral movement.
You can squirt a dab of silicon in each PEX hole in each stud. That will help "secure" the tubing and prevent expansion/contraction noises caused by PEX/stud friction. Another trick is to simply stuff FG insulation into each drilled hole around the PEX. The PEX will slide through the FG, eliminating friction noises as well.
Use plumbing plates to protect the PEX from fasteners driven through the studs.
Insulation, Al plates, pea gravel, sand, and concrete...fuggedaboudit...the PEX will give up the heat, the heat will heat the drywall, which will then act as a radiant panel to heat the room. There's really no need for the thermal mass. The basement is, as you wrote, a somewhat environmentally stable room, and the quick response time of the wall heating will take the chill off in no time at all.
You can add the thermal mass...but there's really no need for it.
Agreed, Thermal mass has more benefit in passive solar situations than in active hydronic. The mass is the heat sink..
Excellence is its own reward!
How about a concrete block wall, with rebar and PEX? Then fill it with concrete. Cheap materials, will work great. A little slower to respond then the low-mass Al-fin wall, but similar to a RFH slab. You could plaster over the block for a smooth-wall finish.
Pea gravel works as a heat exchanger in completely different situations. Like in a small air passages to create turbulent air flow conditions. Or in a "hot rocks" set up where the air being cooled is flowed through gravel one way. Then valves are switched and the air to be heated is flowed through the reverse direction.
But for a steady-state heat application, solid concrete will be a much better heat exchanger than sand or gravel. Get as thin a blocks as you can. Ones with enough space for steel that you can fit the PEX in also.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
I appreciate your help on this.
I'm going to try once more to post a picture of what I was thinking of doing.
From what you've said, it's probably way overkill.
Of course, that would be good, as I'd love to make the project simpler and less expensive if possible.
Even if it's overkill, I'd be curious to know what you think of the idea.
Thanks
Bill
Great picture - Worthy of being in FHB or something.
My concern with adding all that mass is overloading your floor system. Not much chance it's designed for all the added weight. Ambiguous headline: SAFETY EXPERTS SAY SCHOOL BUS PASSENGERS SHOULD BE BELTED
Bill,
First, nice drawing.
For this application, yes, I do think all that detail is overkill. If you really want thermal mass, re-read David's reply on using a fully-encapsulating mass (concrete or sand) vs pea gravel.
Were you to build it as is, the only other thing I might recommend would be a wooden block in between the bottom two horizontal wood members in each bay that the tubing is stapled to. Nothing large, just a 4" square block of wood, with the thickness matching the spacing between the opposing sheets of cement board. I'd screw the cement board into that wooden block from each side of the wall. That will help prevent the cement board and drywall from bowing out in each bay from the weight of the garvel fill.
My only other gripe would be running the tubing vertically. It's not much of a problem, but when and if air bubbles get into the tubing...and on occasion, they will...they'll be tougher to remove with all those loops at the top of each stud bay capturing the bubbles. It'll create a bit of turbulence in the flow, and a bit of noise when the system is running. You might want to consider running the tubing horizontally instead.
Good thoughts, though...
Edit: Forgot one thing...again, referring to your picture...the tubing wil be much easier to run if instead of runing a pure vertical serpentine, you allowed the tubing to cross itself at the bottom of each bay. Kind of like an elongated cursive "l", with the entire wall looking like the white loops on top of a Hostess cupcake.
Food for thought...junk food, but hey...<g>
Edited 10/9/2002 11:20:08 AM ET by Mongo
Thanks, you answered an unasked question I had.
Why everyone talked of running the tubing horizontally.
I never considered air bubbles. Even though it's very obvious once mentioned.
I really appreciate the help. I have a neighbor who has built a very nice radiant floor system in his house. I'm going to have him help me design and put in a system in one wall within the next 2-3 months. Which I will expand later.
I'll be using a TSII Bradford White 75 gallon gas water heater as the heat source. It came with the house, and I understand it has a built in heat exchanger. Unfortunately, I need to move it first, which will involve lots of plumbing, and time.
Another question:
This will be a totally indoor system, although eventually some heat will come from a solar collection system via a heat exchanger, do you recommend a closed loop system w/ antifreeze? A closed loop w/o? Or, another type? And why?
Thanks again for the help.
Bill
Personally, I prefer to keep the DHW and the radiant water separate. Stagnation issues, etc.
Do you need antifreeze? I remember when I lived in Wisco, we had a cold snap where the high temp over 7 days was 22 degrees below zero.
That said...this setup will be in your basement...in interior walls...and even if you do lose power, will the water in the tubing freeze? I'm in CT and don't have antifreeze in my own RFH. If this house is to be occupied year-round, you could opt out of the antifreeze. If a vacation home, you may want it for peace of mind. Still, even when PEX freezes, it does have some give to it. You know your climate better than I do, so I'll leave the decision to you. If you're borderline...err on the side of caution.
Mongo,
What about gypcrete ?
Does it work as well as concrete ? If so, wouldn't it be a major weight savings ?Don't bogart the Ghost
Quittin' Time
Luka,
Good question...
Gypcrete could work just fine, though he'd have to sub it out vs doing it himself. Price-wise, it may run him $27-30 per stud bay to fill the stud bays to a 4' height with gypcrete. some suppliers may add on a few extra bucks for the hassle-factor of a non-standard job.
If he wanted thermal mass, he could mix his own concrete using a lightweight aggregate. That would knock the weight down by about 25%. Still, that'd be in the vicinity of 145 pounds of 'crete per stud bay, about 195 pounds for a regular mix.
The larger issue is if the thermal mass is needed at all. In this application, I think not. thermal mass can be used...but it's not neccessary for optimal performance.
Really appreciate everyone's response on this.
Wow, it'd really add up to that much weight.
Anyone have any preferences on where to purchase the PEX tubing
and the circulation pumps? Also, where's a good source for the heating formulas people have been talking about? I was gonna just put lots of tube in, shut off the forced air vents, fire er up and see how it does.
I'd install one wall, that only has drywall on 1 side. See how I like it, then move on to the places that'd require some demo work. Gonna hire my father-in-law for the drywall replacement, he loves it, I'd rather do anything else.
Anyway, I'm rambling, just hoping to breathe some life back into this post.
Bill
Check your yellow pages for a nearby plumbing supply house.
90% of the time I use Wirsbo tubing, Taco pumps, and Tekmar mixing valves and control boxes.
This HVAC progam is pretty decent.
Wirsbo also has a RFH design manual. Worth looking into. You can get it either from your plumbing supply house or directly from Wirsbo. They advertise them for $25, though they always have sent them to me for free.