Cold floors?
I have a 1970’s 2-family house, upstate NY Saratoga region, zone 5a, electric heat with a full unheated basement resulting in cold winter floors and exacerbating heat loss and heating Khw (13,500 heating Khw for both apartments last winter). The basement has well pump, supply plumbing much of which is below joists, 2 electric water heaters (HP), and I chose to replace the basement overhead garage door with French doors, 3-4 in closed cell spf rim joists (R-21ish), Insulate the basement walls (2-in foil polyiso adhered to block-furring strips (air space)-finished drywall sealed to top plate, & floor=R16ish) all in effort to rid the mice, and protect the plumbing from freezing. The basement ceiling had 1-in foil faced fiberglass with foil facing the unheated basement that created mice runways and was completely destroyed. I removed it completely. I replaced the fiberglass attic insulation (also mice ruined, and compacted) with comprehensive air sealing and R60 cellulose, and I am currently replacing all the windows, doors, and exterior wall insulation (with R20). And by the way I chose to install PV over heat pump as an energy offset over energy reduction. One other detail about the basement is this is a 1 story home encompassing 2500 square feet over unheated basement. Last very cold winter the basement stayed at about 50 degrees, maybe dipping into high 40s during the real cold period. I am after comfort and energy reduction. Do you think I should insulate the basement ceiling, and or perhaps add electric heat to the basement to warm the floors? Should the uninsulated basement cement floor be insulated (xps over it)? I am battling another issue as well with this one. I have tightened the house significantly and continue to do so without a ventilation strategy beyond bath fans. The one side has a humidity problem and they do not use the bath fan regularly. I thought I might install a whole house ventilation and dehumidifier but I can’t run duct work in the basement due to the condensation issue created by the cool basement nor the attic due to the 16 inch cellulose blanket. My interest in adding electric heat to the basement is also to overcome that issue. Any suggestions much appreciated.
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Sounds like you have plenty of insulation. I would expect that basement to be closer to 60F. Generally cold basements are from air leaks, but it does sound like you have addressed most of them. Did you do a blower door test to see where you stand?
Could also be the two HPWH, maybe try to switch those to resistance in the winter and see if it warms it up.
If you have humidity issues, a dehumidifier in the basement should help. It also makes for a great space heater as it run a COP of 2-3 when dehumidifying.
You can also install a single wallmount mini split in the basement and use it to overheat the space. Call it a poor man's heated floors. It would also reduce the resistance heat you need upstairs so overall it will be a cost save.
Good suggestions! I have not had a blower test, but the basement, and house should be on the tight side with a lot of very careful sealing everywhere. The large basement has 2 dehumidifiers going and stays at 38-40% year round. The HP water heaters are set on energy saving where it autos to resistance or heat pump and with the low humidity they may not be running on HP, but I think I will try the resistance during the winter to see what happens. thanks again.
That air gap you left between the foundation wall and the insulation, did you air seal the perimeter of that gap? If you didn't, then air can circulate through that gap, short circuiting your basement wall insulation, and it can bring in moisture too. I usually put the insulation tight against the wall, sometimes with a layer of poly sheet in between. If you need to air seal it, some of the "big gap" canned foam around the perimeter would probably do the job.
I would check for air leaks in the usual areas (rim joist, doors, etc.). If everything is well sealed, then it's probably worth insulating the floor. Your heat must be getting out somewhere! A layer of EPS or XPS on the floor and some plywood above as a subfloor would work, or you could use Dricore tiles if you are concerned about possible bulk water issues.
Bill
Thanks Bill, The basement wall insulation is rigid polyiso adhered directly to block foundation walls. I then fastened furring over (in front of the foil) and installed drywall on the furring that created the air space. I noticed that space must be sealed. I wrapped the bottom of the drywall with aluminum faced flashing tape to protect in case of ever a flooded basement about 3 inches high both sides and then caulked the seam to the concrete floor. For the top I foamed the top back to join with the rim joist ccspf. The drywall then was finished tape, and 2-coats satin latex paint for durability. Its a pretty sealed assembly. I figured if ever there was any moisture penetrating through the block it would run down the back of the iso into the french drain that sits underneath the wall assembly. I replaced the basement windows with a tight window and sealed carefully also. I think the weak spot is the french doors but I am careful to limit using that exit during the cold weather and opt up/ down the basement stairs. I see you recommend insulate the basement floor and I agree that is a good idea. My cold first floor over the basement sounds like it should not be happening, right? It is a rather large basement space though at 1731 sqft, and another 350 sqft. crawl area (4' tall) that I insulated the same way (spf rims, & finished continuous insulation assembly) that is wide open to the main basement. Do you think just the mere size of the space could be eating my upstairs heat loss to maintain the 50 degrees? I can envision your xps suggestion on the basement floor may help hold that and bump me up. I only have 90-inches to bottom of joists. Do you think 1/2 xps would be ok or would you go more? We do set back our heat but not as much as we used to. The electric baseboard is a cast iron radiator inside the tin baseboard units that radiates heat after the tstat shuts it off. Do you think by setting back the temp I am undermining the basement temp too much? thanks again for your suggestions.
If you don't have any issues with air leaks, then insulation is all that is left to cut down on heat loss. Your basement seems *very* cold though, which makes me wonder if you're missing something somewhere. My own basement gets into around the mid 60s in the winter, and I only have about half of the walls insulated, and the crawl space isn't very well air sealed (yet -- that's a project for this fall). The crawl space gets into the 50s, but we keep the door to that shut during the winter, so the rest of the basement is reasonable. Your own basement is so much colder, that's what makes me wonder if you still have some air leaks somewhere. A blower door test would be able to check for this.
Assuming you do NOT have air leaks, you are probably losing the most heat through the walls, then the floor, in that order (assuming no insulation), since the floor will "see" a lower thermal delta to the earth than the walls. Make sure you have the walls insulated, which sounds like is the case in the basement, but have you similiarly insulated the walls of the crawl space? You want to insulate ALL the walls and ALL of the rim joist as a first step, at least to code minimum (typicall R10-R15 for most Norther CZs). If, after that, it's still too cold, that's when you want to look at insulating the floors.
The crawlspace floor is probably the biggest offender, especially if it's above frost depth. You can try an insulation "skirt" around the perimeter as a first step, or just insulate the entire thing. The issue with crawl spaces is that the floors are usually uneven and/or just dirt, so rigid insulation can be tricky since it tends to break up if you have to work in there in the future. You could do a "rat slab" (thin concrete slab) first, then insulation, or insulate and try to not go into the space. It's also possible to put a wood subfloor over the rigid foam, and do a good job of ground prep before insulating so that things are reasonably flat and even. The more you do, the more it costs, obviously, so you need to determine what's most important to you here.
The basement floor is easier, but is probably the least of an issue in terms of heat loss, so I'd look at insulating that as a last step. This means (1) look for air leaks, seal any that you find, (2), insulate the walls of the basement AND the crawlspace, (3) insulate the floor of the crawlspace, (4) insulate the floor of the basement, in that order. check any exterior doors (you mentioned a "french door") that go to the exterior too, which are usually weak spots in the envelope.
Another thing to remember is that the basement will always be colder than the rest of the living space if you don't actively condition it, regardless of how heavily you insulate it. That means you will need to put some amount of heat into the space. Usually this is done with an extra register or three with a forced air system, or a radiator or two with with a hydronic or baseboard system.
Bill
Yeah, I anticipated, and was extra thorough with continuous insulation around the entire perimeter including crawl space. Our crawl does have a cement slab floor but is above frost and I will start there for sure. In your basement at mid 60's is there a heat source? This is why I reached out for advise because I currently have no heat down there. It is actually heated by the heat loss from above. But that arrangement is leaving us with the cold floor and only a 50 degree basement. I thought, maybe I should insulate the basement ceiling and put electric heat down there ( i would also xps the basement floor). But I insulated the walls because of the plumbing and water heaters down there. Is the solution to put some heat down there and due to the low delta of the conditioned space above there will not be a heat loss so I don't insulated the basement ceiling, XPS the floor, and run the HP water heaters on electric (as mentioned earlier) in the winter? thanks
The more I think about it, the more I'm sure the issue is the two HPWH.
In most basements, you would have either a boiler or a furnace with ducting to supply the heat for the water heater.
In your case it has to pull it from from the living space above. The space has to get pretty cold to move any BTUs from there, thus the cold floors. Never mind the heat loss through the rest of the envelope/slab.
Also since your space heat is resistance, there is no benefit of running them in heat pump mode in the winter as all the heat is eventually supplied by your COP 1 space heat. If you want better DHW efficiency, you can look at adding a drain heat recovery pipe. This could be shared by both units and feed the cold water supply to the tanks.
I never would have thought the HPWH could effect that large of a space temperature very much however I will definitely try them in resistance mode. I replaced older electric water heaters hoping for less KWh but the space heating and it’s energy consumption and comfort are the primary concerns. thanks again for pin pointing this issue.