Second floor radiant heating
Hi,
I installed heat pump, staple-up hydronic heating in our first floor (from the crawl space), and we love it. We are now building out our second floor, which right now is only a conditioned attic. The house is from 1915 so the first story is not well insulated but the second story will be. In winter the temperature of the unconditioned attic second floor is ok but not nicely warm, I am concerned that our 1st floor radiant heating will not suffice when we build out the 2nd story.
Can I install hydronic heating loops into the 2nd story floor from the top? I would have to staple the aluminum plates on top of some baseboard and then another baseboard on top of that, or how would this work? Or do I need to remove the ceiling of the first floor and install it from there?
thanks Heiner
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There are systems like WarmBoard that go over a subfloor and under finished flooring. They tend to be expensive so people do DIY solutions with strips of plywood between the tubes.
I'm a little puzzled with this statement:
"The house is from 1915 so the first story is not well insulated but the second story will be. In winter the temperature of the unconditioned attic second floor is ok but not nicely warm, I am concerned that our 1st floor radiant heating will not suffice when we build out the 2nd story."
Usually the problem with floor heat in new construction is that the heating load is so low that the floors never get toasty warm.
I highly recommend doing heat loss calculations. We can help you with them.
Check out the Warmboard-R product. It's thinner and cheaper than the standard Warmboard, and designed specifically to go over an existing sub-floor. As DC said, a lot of people try a DIY approach. But the problem with that is the aluminum channels and facing. It's not enough just to fill gaps with strips of plywood. That does nothing to distribute the heat from the pipe over the floor surface.
https://www.warmboard.com/products/panels/warmboard-r/
Since we’re throwing around some expensive options I’ll toss out Messana Radiant drywall panels as another option.
You could just rip ply to fit between joist like you would on a retrofit curbless shower and make them at the depth of tubing. Then to transition tubing between joist bays just go through center of joist like any other plumbing pipe. You wouldn’t even need to sister joist the whole length, just occasional blocking to catch ply. You could also use a radiant ply to direct the heat if so inclined.
I've done that and then placed sand/cement mix around them. A sheet of backer board goes over, screwed to the joists, and then tile.
If you're doing wood floors above, you can staple Omega radiant plates over the tubing into the plywood, something like: https://www.supplyhouse.com/Mr-PEX-6110702-Omega-Aluminum-Heat-Transfer-Plates-for-1-2-Tubing-Box-of-100
To match the thickness of the rest of the floor, you want your plywood rips to be flush with the tops of the joists, and then a rip of the subfloor material across the top of the joist to get it up even with the rest of the subfloor.
im having ecowarm done for the 2nd floor of my new build. around half the cost of warmboard. 3/4" plywood panels going over the 3/4" plywood subfloor.
Yep, you can totally add hydronic heating to the second floor from the top. Just staple the aluminum plates onto some baseboard, then layer another baseboard on top for protection. No need to mess with the first-floor ceiling. Insulate well to keep the heat in.
Hi All,
thank you! Warmboard/ecowarm looks great and simple. For 1500sqft, ecoboard seems to be around $10K+, right?
@DCcontrarian: What would be the problem of a too low load? Yes, maybe the floor wouldn't be super warm, but what would be the solution for this problem besides using bad insulation? Or are you suggesting that no heating system is needed at all?
@freyr_design @DCcontrarian: I am not sure if I could follow your proposal. Are you suggesting to install bridges between joists, then layer plywood onto the bridges, between joists, and then carve trenches into the plywood to hold the loops?
my ecowarm quote is around $8 a sq ft (935 sq ft for 7400 shipped).
This is my suggestion, and I believe what DC was suggesting, but I could be wrong on DC. I think it would price out much cheaper than $8 SF but you can do the math.
Yep.
I like that for tile, as you can use your joist for screed boards
I did that in the first heated floor I ever did, circa 1999. I let the sand mix set up between the joists, then I troweled down a thin layer of thinset mortar and dropped the backer board onto it then screwed them down. That base was so solid!
Twenty-five years later I still look back on that floor with pride. It was so nice underfoot. The other nice thing was it abutted a hardwoord floor and I got the height of the tile exactly even with the height of the wood so there was no lip or transition.
These are great ideas and going into my "ideas file". Thanks.
But just so people coming onto this discussion string in the future, there is a structural engineering impact people should be aware of. In areas with strong lateral loads, i.e. high winds or earthquakes, the floor sheathing serves an important structural function as a shear resisting plane. It must be continuous to do that and these ideas destroy its shear capacity. So before going this route do check on the structural impacts.
That’s a good point, though my suggestion keeps diaphragm intact, dc wood floor, if adhesive is used between ply, I imagine would perform very well. I imagine the tile would as well, but it is certainly not prescriptive.
thanks for these great sketches!! I am sure it is much cheaper but also a lot more work. These warmboards even obviate the need for drilling through joists. The joists in our house suck because they are not equidistant, and hence cutting the ply would be very time-consuming. I like the idea, though, and it's great that it does not increase the height of the floor.
A couple of notes:
-if you already have a subfloor, just go with DC suggestion and tip 3/4 ply and run pex in between. This would cost about $1200 and require approx 100-150 rip cuts, half that if you stack sheets. (I would happily fly to CA and do the cuts for a mere $7000 and you could still save around 2k….)
- if you don’t have subfloor, again, you just get a piece of paper and measure your joist and do the req 100 rip cuts. It will take you a few hours- day. Sistering on a 2x4 or blocking would also only take a few hour- day. Again, I would happily fly down and do it for a mere 7k
- if you are worried about your joist strength, do a full width sistered 2x on either side and you will actually make your floor much stronger. And drilling through the center will not be detrimental to the strength.
- the only benefit to warmboard is the insulation, which you don’t need as it is conditioned space below.
It is not a lot of work, especially if you have a helper, even without one those time estimates are probably still accurate.
Hi freyr,
if I keep the existing subfloor which is above joists (not between as in DC) then I can just do regular cuts and it may make sense. Measuring the joists and doing individual cuts is extremely time consuming (I did it for insulation).
One other thing I am concerned about is heat distribution. The warm boards snug fit the PEX allowing nice heat transfer to the aluminum. Without any aluminum I am worried that the heat transfer into the wood is much worse.
FInally I believe I would need to fix the PEX pipe to the wood floor, like some metal bracket every 2 feet or so.
I could screw aluminum heat transfer plates from the top addressing both concerns above, but that would be another ~5K.
Omega heat transfer plates will hold the tubing in place and help with the spread. Something like this:
https://www.supplyhouse.com/Mr-PEX-6110702-Omega-Aluminum-Heat-Transfer-Plates-for-1-2-Tubing-Box-of-100
In terms of what kind of heat transfer you need, you really have to do at least back-of-the-envelope engineering with a heated floor. What is the heating load for the space? What floor temperature do you need to cover that load?
If it's really space built to modern standards the heating low is going to be quite low and so will the floor temperature.
These ones are substantially cheaper.
https://m.vevor.com/floor-heating-mat-c_10381/200pcs-4ft-aluminum-radiant-floor-heat-transfer-plate-for-1-2-pex-tubing-hotel-p_010297265286?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=21317537891&ad_group=&ad_id=&utm_term=&gad_source=1&gbraid=0AAAAACq8bLX4CJtnBsOSwJoy7sZ0yWp1a&gclid=EAIaIQobChMIsu32n_yihgMV1YnCCB0r6QAaEAQYASABEgJ-xvD_BwE
Maybe it still makes sense for you to go the warm board route, I just think you will end up spending 25% if you do the diy route. Also maybe it gives you a chance to buy a new tool! (Track saw might be nice)
> the only benefit to warmboard is the insulation, which you don’t need as it is conditioned space below.
This was my assumption going into our house build, but the designer informed me that Insulation is still required when installing radiant above a conditioned space. The minimum underfloor recommendation for our 2nd story was R15 at the time (2017).
"What would be the problem of a too low load?"
You spend all that money for heated floors and then the floors aren't perceptibly warm.
Presumably you're going to have air conditioning anyway, which requires either minisplits or ductwork. In either case, it can be used for heating too and you might end up with the same level of comfort.
even without perceptibly warm floors, I prefer radiant floor heating due to:
- no hot/cold spots
- no noise
- invisible
But yes spending 15k on an unnecessary radiant floor is not worth it.
I am not even sure if we need AC, it never gets too warm in the Bay Area.
Does anyone has experience in using radiant floor for cooling? Does this work or is only the floor cool and everything else remains hot?
Radiant cooling does provide effective cooling of the space. But it can't remove humidity without creating condensation on the floor (which wouldn't really remove it unless you mop regularly and wring the mop out into a drain), so in most climates you have poor comfort and the risk of moisture on the floor. So you need another way to remove humidity and you need a fancy control system to avoid condensation on the floor. Which is possible if you really want it but rarely practical.
> Does anyone has experience in using radiant floor for cooling? Does this work or is only the floor cool and everything else remains hot?
Our house is completely heated and cooled from the floor. (3477sq/ft well air sealed and insulted build in Boulder, CO — Warmboard R + Tekmar controls + Nordic ATW heat pump). Cooling works great – more comfortable than air cooling in my experience. We have ~0 latent load here, so there's no supplemental fan coils for dehumidification, but the controls would support this. With summer days that often hit triple digits, the cooling has been well tested.
If building again, I'd go with this approach in a heartbeat. But it takes way more planning (e.g. detailed design) and budget than other options. Beyond the Warmboard costs, you need to price out any additional circulators, manifolds/zone valves/etc, and controls. Do you need to add a buffer tank or adjust the existing tank's size? These costs can add up quickly.
Whether you need cooling and/or dehumidification varies widely across the Bay Area (Walnut Creek is a totally different climate than SF). The trend I've seen over the last few years (I'm in Menlo Park about once a month on business) is that temps are rising pretty significantly. I'd definitely provision for cooling.
thanks this sounds great. My heat pump supports a moisture control unit. I am in Menlo Park and my inner temperature seems to be 5degree less than everyone else's, ie 90F inside is a good temp for me so I will rarely have to cool.
I lived in Concord, CA for years and never had AC. It wasn't even a very well insulated house, built in 1953 with minimal attic insulation. It had a shaded back porch and on the hottest days I'd leave the patio door open. The breeze was enough to keep things comfortable.
Was it a perfect 72 deg, 50% humidity? Nope. Was it comfortable? Yup.
I've had good luck with ultrafin for retorfit install. Pull up the subfloor, air seal the joist ends and install batts against the ceiling bellow.
The nice part about ultrafin is you can run the pipes either way not just along the floor joists, I find running perpendicular the easiest provided you drill slightly larger holes. You can adjust the spacing and the number of heat fins to get the right amount of heat you need especially with the lower temp your heat pump provides. The ultra fins do require hotter water for the same BTU/sqf output than heat spreaders but it very simple, much cheaper and quicker install.
New subfloor and you can install any floor finish you like.
The nice part about these is they are far way from the finished floor so there is no chance of putting holes through a pipe with an errant nail.