Hello,
I am new to this forum, but a decade long reader of FHB. I have an unfinished basement for which I want to install a staple up radiant heat system. I would like to know the opinion of any who have hands on experience with this type of installation with regards to best materials to use and the best way to lay it out.
The system I am installing will be a closed system with a 750 gallon water storage tank that will be heated via solar collection panels and a wood stove heat exchange if necessary. I plan to install a heat exchage loop through this tank. My home has 2-1/2″ oak flooring on the main floor – where I want to do the staple up. I currently heat with a wood stove in the slab on grade basement. Because I’ve not insulated the floors, the wood stove currently does a masterful job of heating my home. I just want to cut back on the amount of wood I need to cut from year to year.
I’ve read a great deal about radiant flooring online from the companies that sell product for this type of installation. I had decided on pex-al-pex 1/2″ tubing thinking that it would have a greater thermal conductivity and be easier to work with as it bends into shape and holds it’s shape rather well (or so I’ve read) along with heat transfer fins. So I requested a quote and the on-line rep thinks I would be better to use pex-b. So now I’m wondering what materials would be best.
The question I have regarding system design is if a header system or home run system is best.
Thanks in advance for any and all advice
Shenandoah Valley Dave
Replies
This will serve as a bump.
I've got radiant in slab. No run of tubing is over 300 ft. The first place the tube goes is along the outside walls and the centers of the tube at the outside walls are tighter (6" vs more interior of the structure-12")
On one zone I have 3 runs of tube coming off a manifold by the boiler. Another zone in the same level has just one loop.
No staple under subfloor here, though we did lay on top of the subfloor between sleepers, then 5/8's plywood and ceramic on that.
Probably don't lay under kitchen cabs, but do get a run by the toe kick.
Ring around the toilet, but not too close, might melt the wax ring. We have no problem with that and yes it's true-the seat is warmer with radiant.
Best of luck.
Use the pex-b. I just used pex-al for my system and it is so hard to deal with and I did it from above the floor. It will be a PITA to get pex-al in joist bays.
I have a home run system, but my loop is only 350 feet.
it's very unlikely solar is going to contribute a significant amount of heat to your building unless your heat load is tiny or you have a huge solar array.
Also, it's even more unlikely that most joist systems will operate at a water temperature low enough to maintain a comfortable room temperature at the point a solar system is likely to get a 750 gallon tank. This seems like a bit of a suspect plan from the get-go.
the one good think I could say is that if the wood stove heat exchanger is lower than the tank especially, you could do an unpressurized tank and forgo a lot of explosion risk, so that's nice. maybe with a nice drainback solar system. still need a dump for the wood stove exchanger though.
You definitely want a heavy gauge plate for this, not a "flashing grade" plate. You definitely want real insulation in the joist bays, not some shiny foil making huge claims. and you definitely need a real heat load calculation (no "energy factors" or other such voodoo) to know if this is even worth doing in the first place.
that's a pretty big array. how many BTUs/day average during shoulder season and full winter are you expecting?
manifolds are WAY better than headers. use balancing valves on the loops. do NOT run multiple rooms on single loops. isolate.
I used a chart for 40degrees lattitude (farther N than my location). The BTUs from equinox to equinox through winter solstice never fall below 350,000 per day. But that is assuming the collectors work at 100% for getting the BTUs from the sun. I think a conservative estimate would be at 60% which would put the collection at 220,000 BTU minimum at the equinox and 250,000 BTU per day on the solstice. I believe these collectors will be at least 80% efficient (from the data I've seen on a similar collector). That would but equinox BTU at 290,000 BTU min and solstice BTU at 340,000 BTU min.
The design I want to use has mixing valves connecting the feed side of a loop and the return side of the loop. Is this what you mean by balancing valve - sometimes we just have different vocabulary for the same meaning but end up confuddling one another.
Also, design wise, I had intended to install all my first floor 1500sq ft on one zone (thermostat) with (6) 250ft loops. Is this what you mean by isolate?
Thanks again for your time in answering my questions,
Dave
I mean you want to be able to balance flow through individual loops. Equal lengths are fine only if you are only heating one room, otherwise it is much more important to isolate rooms on their own loops, even if you use one zone.
sounds like your average collection would be less than 10,000 BTUs/hr average. That's a pretty low heat load. You better have one sweet envelope if you are going to heat 1500 square feet with that. It will definitely reduce the amount of wood you use, though.
I have DIY staple up in my house
I have two manifolds, one for the first floor one for the second. Each manifold is a zone. With our floorplan and use there was no need for additional zones.
I have 10 loops on my first floor, 8 on the second. Each loop has a balancing valve so I can tweak flow a little here and there. After the initial setup, very seldom do I mess with the valve settings. Maybe once a year. Each loop is in the 220-250' range and covers 5-6 joist bays.
I have no aluminum plates, just PEX stapled to the underside of the subfloor. 1/2" foil faced polyiso under that on both floors. In the basement, another r-19 FG bats under the polyiso. R-13 on the underside of the polyiso on the second floor.
I circulate 115 degree water. Pure comfort, no issues. An oil-fired boiler heats water for the RFH (closed loop) and domestic hot water. A mixing valve knocks the water down to RFH temps.
On top of the 3/4" subfloor, I have 1/2" ply underlayment, then brazilian cherry flooring throughout the house, except slate in the foyer and tile in the laundry room and in the kids' bathroom.
House footprint is roughly 34' by 46', roughly 1500 sqft per floor. I reserved two headers on the second floor manifold to eventually heat my walk-up attic, but no need. About 850 sqft of finished space up there. Attic is well insulated, I still have a full blanket of snow on the roof, everyone else's roof has been clear for almost two weeks.
I'm in CT. Everything was DIY. Back then when I installed it I didn't know what I didn't know, but hey, it works.
Sounds like your collectors will be DIY? I've been scratching my head contemplating a solar piggyback of sorts to add a little heat to my hot water system. But I'd want vaccum tube collectors for best efficiency, especially with overcast winter skies. I've got the perfect roof to place them on...but from the solar perspective, I'd have to drop two monster oaks that shade the south side of my house. I don't have the heart to drop those trees though. Too purdy and I enjoy the shade too much. Catch-22. lol
Thanks for the info
Thanks for sharing Mongo. I have been debating the heat absorbtion plates. I have a co-worker who has a staple up job without plates and he is enjoying his heat. He has an outdoor wood boiler and I'm not sure what the circulation temps are for his system. Since mine is going to be installed in an unfinished basement for a 1400sq ft 1st floor, I will have a season or two to decide if I need them - so I'm leaning towards installing without for now. The 2x4 trusses as opposed to solid joists will, I think, make the install go alot smoother.
The reason I've been waivering between a header for distribution or a manifold is the best location for plumbing is at one end of the house, which will mean home runs from the far end of the house (roughly 46ftx28ft) will use up 35-50% of the loop length. But from what I am reading here, it seems like the manifold at a consolidated point will be the way to go - so I'll probably do that.
I'd recommend a manifold...
I'm in the same boat design-wise, my boiler is near the end wall of my house. So I located the manifold mid-span on the main beam of the house and ran 1" Cu from the boiler to the manifold. It made the loop design, installation, and balancing so much easier. It's one of those thing that at the time you think it's costing you time and money to install the manifolds, but in the end it saves you time and gives a better installation and better performance.
Your trusses will make it very easy to install the loops. I kinked my first two pulls before I got the hang of pulling and twisting the PEX into a loop in the restricted space of the joist bay. Fortunately those were my only two, I've never kinked one since.
without plates, you max out your output at something like 160 deg F. at 20 BTUs/sq ft under wood.
I have designed many plateless systems, but typically only in very low load situations. I have also troubleshot an awful lot of naked staple up that failed to perform because the person putting it in had no idea what it could and could not do.
If mongo is using 115 degree water and keeping up all winter, then his maximum load is very low, like 10 BTUs/sq ft. he got very lucky indeed... almost no one has max loads that low. unless he likes 60 degree rooms, or has reliable and significant heat gain from other sources.
I'm pretty typical construction...
Typical 2-story construction, 2x6 walls, FG batts, Tyvek. First house I ever built, all DIY, did it before I knew what I knew, thus the FG batts. Marvin windows, nothing exceptional in terms of solar gain.
First floor typically holds 75 degrees, second floor 71, attic 68.
On the negative (thermal) side, two woodburning fireplaces, one on each floor. Standard cast iron (leaky) firebox dampers, no caps on the tops of the flues.
TJIs 19.2" oc instead of 16", two runs of PEX per bay.
Open stairway to the walk-up finshed attic, another 850' of unheated space up there, it stays warm with residual heat from the rest of the house. Cathedral ceiling is well insulated compared to the neighborhood, my roof is the only roof to hold snow.
Can't give credit to incandescent bulbs, I'm pretty much all CFLs.
Home sweet home!
What is your location? Solar hydronics ... hmmm ... I agree w/ the other poster. If you RELY on solar w/ wood heat backup, you're likely to still be stokin' your wood burner ... which you will have to modify for hydronics.
38:26:5 N lattitude
Location is 38:26:5 N Lattitude - in the Shenandoah Valley of Virginia. I plan to keep the wood stove in the basement for the first year of this "experiment" so I'll be able to heat the home regardless of how the solar heat system works.
If the solar collectors don't collect enough heat once I have the radiant tubes installed, I would probably end up with an outdoor wood burner. I don't think having an outdoor burner heating a 750gallon storage tank would be to hard to set up.
You can buy wood fired boilers that are exactly what you are talking about. Don't know the specifics about the solar climate, but I'm guessing you won't have enough solar resources (and panels) to do the job.