Thanks Dana!
This is a college house that is about 1 block from campus in Stillwater, OK (Oklahoma State Univ.) where our son goes to school.
It does get cold there on a regular basis so a heat pump doesn't suffice. We actually have a mini-split for the AC in that room that has a heat pump heater. It works great till the temperatures drop too low (say upper 30s/40 degrees) then for the remainder of the winter it just cannot keep the room warm.
The other thing that the wall heater does is heat an adjacent bathroom. There is no vent into the bathroom but the wall between the bedroom and bathroom are shared so the heat goes in there with no issues.
Additional details/goals:
1. The windows are terrible. You can clearly hear conversations happening on the street outside the house.
2. The west facing window is three windows spanning approx. 8ft. There is an additional window facing north that is standard size.
3. The longest bedroom wall is north facing.
4. Goal is to buy the most reliable/efficient unit that will fit the opening the current unit is taking because the walls are knotty pine paneling and I have no way to patch the walls.
Does anyone have quality or installation concerns about the Home Depot model here:
Or do you have any other suggestions for ordering online a wall heater that will take approx. the same wall space? A shorter heater will leave holes with no paneling - so I need the full length heater.
THANKS!
Diana
I know people living in central Vermont heating an entire house with just three cold climate mini-spits in a location that regularly hits double-digits below zero. A heat pump definitely DOES suffice- it just has to be specified correctly for the heating load, not just air conditioning. The
99% outside design temperature for Stillwater OK is +36F, it doesn't need cold climate version for that, but it does have to be sized correctly to the load, and leave it on during cold weather- don't use overnight/away set-backs the way you might with an oversized gas-burner.
If it isn't crapping out until it's ~40F or cooler outside it means your existing mini-split (got a model number?) is only slightly undersized for the current heat load. A lower-end 3/4 ton mini-split might only have 9000 BTU/hr of heating capacity , but that SHOULD be able to keep up with a reasonably tight 600 square foot apartment over a garage. The fact that it isn't keeping up at those temps is a fairly strong indication that there's a lot of low-hanging fruit on the building performance end.
Air sealing would be the cheapest building upgrade, but beyond that...
An uninsulated wood floor over an open-joist garage loses about 0.4 BTU/hr per square foot per degree-F. So assuming the garage stays at 40F with the door closed that's a 30F difference a 600' floor would be losing 30F x 0.4 x 600'= 7000 BTU/hr. Stuffing even some cheap contractor-roll R11s tight to the subfloor would reduce that to 0.1 BTU/hr per square foot per degree-F, or 1800 BTU/hr, better than 5000 BTU/hr reduction in heat loss. That could be as much as half the heat loss of the apartment in it's current leaky-window condition.
If the garage ceiling is open the subfloor can be air sealed with caulk or housewrap tape, then insulated with R13-R20 batts snug to the floor, taking an even bigger chunk off the heat load. (R19 would be IRC 2015 code-minimum for floors in US climate zone 3) But if it's closed up blowing it full of cellulose would still reduce air leakage and warm up the floor by quite a bit. Assuming 500 square feet and 2x10 joists that would take about 400-500lbs of cellulose, for about 50 cents/lb, and would deliver R35-ish performance. Fiberglass of similar volume might be cheaper. (Box stores in my area usually throw in a free day of rental blower if you spend more than $100 on the insulation.)
If the windows are leaky but functional single pane windows are single-panes, spending some money on l0w-E storm windows and some air sealing & insulation measures would be a good investment in comfort & efficiency making it quieter and more air tight. (It's fine to put them over leaky clear-glass double-panes too.) Not counting the air leakage, single pane window loses about 1 BTU/hr for every square foot of area per degree of temperature difference. At a 35F temperature difference it's 35 BTU/hr per square foot. Four windows at 10 square feet each is 40 square feet x 35 BTU/ft-hr for about 1400 BTU/hr. Low-E storm windows would cut that down to ~400-500 BTU/hr (a 900-1000 BTU/hr cut in heat load), and makes the place more comfortable at any temperature. Larson's low-E storms sold through box stores are good enough, but if you're keeping the place long term it's worth up-grading to the next higher quality in their lineup (which is usually a special order when going through a box store.) The better-grade Larson storms are more air tight, and have better latching hardware, etc.
Even though the low-E coating is an upcharge from clear glass, it actually pays back quicker than clear glass despite the higher upfront cost. A low-E storm window over a wood-sashed single pane is very comparable to (and sometimes beats) the performance of a code-minimum replacement window that's more expensive up front and harder to install. They also deliver a pretty big cut in air conditioning load, which is pretty high for west-facing windows that aren't easily shaded by overhangs, etc. In my area 32" x 55" low-E storm windows for double-hungs run ~
$80/each at box stores, ~ $90-100 for better-tighter versions.
Cutting the load by 900 BTU/hr is probably something like 10% of the total heat load currently, and would be an even bigger fraction after some air-sealing & insulation upgrades have already cut the heat load down to size.
Filling in the finish wall where the old one stood with an aesthetic complementary wall type shouldn't be too tough, but could take some creativity. Trying to color & grain match knotty pine would not be easy, but a contrasting type of wall in a floor to ceiling strip doesn't have to look weird.
Don't know anything about the reputation of the Williams wall furnaces.
The one in the link is a millivolt thermostat no-electricity required model with a remarkably low AFUE of 71%, and 19,200 BTU/hr of output (about the same capacity as as a no-frills 1.25 ton mini-split). It would still be able to heat the place during a power outage, but last time I looked Stillwater OK was still in a first-world country, with first-world type grid reliability, so that's not an essential feature.
