Should you heat an uninsulated basement with your hvac system or use portable heat
Hi as always thanks for all the advice I get on this forum. I’m in climate zone 4, nyc area, Basement is going to have dmx one step with a vinyl floor, rim joist will be insulated with 2in eps. Nothing else is insulated. The room I want to heat is about 12×20, with 3 egress windows, the area is closed off by doors to separate areas so there will be some heat loss from doorways and windows. I have an available duct so I could heat and cool the space with my gas furnace and electrical ac. My other option would be to just turn on a portable heater or ac when someone is down there. What would be a better option. Will I be wasting money and heat by having a duct open in basement? Will it be impossible to even heat a space like this?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
In general it's best from both a moisture and energy use point of view to air seal & insulate only the exterior walls & band joists, but do the ENTIRE basement, not just one room.
At 2" EPS doesn't meet the IRC code minimum continuous R10 for basement walls in Zone 4 (which is also NY state code minimum)- it takes at least 2.5". Instead of EPS, using 2" of foil-faced polyiso strapped to the wall with 2x furring through-screwed to the foundation would get you there, mounting the wallboard on the furring. Taping the seams of the foam with purpose made foil tapes, and caulking/foaming the foundation sill & band joists is also important.
The heat loss characteristics of basements are dramatically different from fully above-grade spaces, so they don't really zone well together. With continuous R10 from the slab below to the subfloor above the heat load of that 240' basement room is going to be very small even if the rest of the basement isn't actively heated. An uninsulated partition wall with wallboard on each side is good for about R4= U0.25 BTU/hr per degree-F difference. Assuming a 55F basement and a 70F office space with one 8 x 12 and one 8 x 20 partition wall (224square feet total) the losses to the basement are only:
U0.25 x 224' x (70F-50F)= 840BTU/hr.
With a fully continuous R10 on the foundation walls the exterior losses are about the same or even smaller, despite the bigger delta-T above grade where the 99% outside design temp is ~+15F (in most of Westchester, NYC, L.I.). Assuming a total of 20 square feet of code-minimum U0.30 window, the window losses are about
U0.30 x 20' x (70F -15F)= 330 BTU/hr.
Add it all up and it's about 2000 BTU/hr, or (/3.412 BTU/watt-hr =) 575 - 600 watts. If it's for intermittent use and comfort isn't at a premium, a 1500watt baseboard or space heater on a thermostat enabled by an occupancy sensor would work just fine for heating it up quickly.
But give serious consideration to air sealing and insulate the ENTIRE basement. Even when not actively heated a 55F basement represents a significant heat load that you're paying for in both gas use and comfort. In your area during summer an un-sealed uninsulated basement also represents a significant latent cooling (humidity) load, without an accompanying sensible (temperature) cooling load, which makes room air conditioners somewhat useless, and often requires a dedicated dehumidifier to keep the mold and "musty basement smell" at bay. Air sealing and insulating the exterior walls of basement goes a long way toward reducing those loads.
For me it depends on how often I planned to use the room.
If I was sure I would be spending several hours 5 or more days a week in the room I would connected it to the current furnace.
If I wanted good control of the temp in that room I would consider putting in a mini split unit just for that room.
The portable AC units I have seen were largely ineffective having only one hose blowing out of the house. There are 2 hose units but they seem pretty Mickey Mouse to me. Portable space heater can be very expensive to operate depending on your utility rates and I consider them to be fire hazards.
“Will I be wasting money and heat by having a duct open in basement? “ Yes it will cost more money to heat the space than to not heat the space.
"Will it be impossible to even heat a space like this?" I have a hard time thinking of anything that is impossible today or tomorrow but yes it will cost money.
Walta
Why not just put a damper on the duct?
The energy savings from closing off a room is smaller than you think, you just end up with a cold interior wall.
Thanks for all the input as well as the math breakdown from Dana. I fully intend on insulating the entire basement, problem is I’m building an addition within 1-2 years. Architect told me: 1. I could put down floors but walls would end up being ripped out. 2. Code required insulation in my town is R21, unless I heard wrong. 3. When inspection for addition comes if I have anything on walls they will be giving me a hard time and make me meet very strict requirements.
The damper would be a good idea, the space heater idea is good as well. Rooms I’m separating are a mechanical room, laundry room, and storage. The area I want to use is for a playroom that my kids can use their bigger toys. Probably 1-2 hours at most down there during the day. If insulating the rim joist isn’t going to do much or if you think this room can not be comfortable at any point I won’t bother until I insulate the whole wall. Just looking for a temp solution for the time being, get everything up to par later.