Heating a Detached Garage Being Used as Home-School Classroom
Hi All – I am remote schooling 6 children in a detached garage in Boston, MA. The garage is 18×19, vaulted hip roof ceiling. The walls are insulated with old fiberglass kraft-faced batts (2×4 studs), covered with 1/4 MDF. The Ceiling roof is insulated has 2x6s rafters and fiberglass batts and is drywalled with 2 coats of mud. The windows are single pane, maybe 70 year old divided lite windows. There are five, they are about 24×48, rope and weight sash. There are two garage doors, uninsulated and once egress door.
After initially looking to heat the space with a 7,500W heater, the electrical upgrades necessary (over $3K) were too expensive. Talked with an Aerobarrier company, who thought it would also be too expensive to use them since (we hope) this is temporary.
的建议是减少体积pace we are heating by getting 1″ 4×8 sheets of foil faced rigid insulation and laying them across the chords creating a ceiling (I would also tape the seams of said boards and will be duct taping the small interior gaps on the garage doors as well as adding weather stripping the garage door). Each child would get their own heater so that the heat is directly on their space, allowing area close to the child to be heated. Thus, we would not be trying to heat the entire garage. We would also put plexiglass on the interior of the windows to stop drafts.
The reality is that the garage space is not going to get school house warm – 68F-72F. Most likely we will end up in the 55F range, but with the heaters with each child, hopefully they can stay warm. I believe in this plan. Are there any other suggestions or alternatives to this plan that folks would recommend that would be temporary and would not break the bank? I am climate Zone 5.
GBA Detail Library
由气候和房屋部件组织的一千个建筑细节的集合
Replies
A ceiling as you describe would reduce the total volume of the space to be heated, which would make it easier to keep warm. Heat tends to rise, so high ceilinged areas do tend to feel a little cooler down below. The reduced surface area of external walls will also help reduce heat loss a little more. Technically that's not a code assembly though, unless you used something like Dow Thermax (more expensive), and even that MIGHT be an issue on a ceiling -- I'm only familiar with it's use on walls.
I would recommend the use of 1/16" PETG on the windows instead of plexiglas (acrylic). PETG is an acrylic/polycarbonate blend, and it's MUCH more durable than acrylic but not as expensive as a polycarbonate. You don't need a lot of thickness either, since the insulating work is all done by the air you trap between the window pane and the temporary plastic layer (similar to how a storm window works). Acrylic alone is very brittle and tends to shatter on impact, PETG is more like polycarbonate and will bend instead, which is better and also safer.
A 7,500w heater would probably need a 40 amp, 240 volt circuit. You can get 5,500 watt "garage" heaters that will work on a 30A, 240 volt circuit which will be a lot cheaper to install. I'd suggest you look into that before you put in multiple small space heaters. A typical space heater is 1,500 watts, and is designed to completely max out a typical 15A, 120 volt residential circuit. What that means is if you want to run 6 such heaters (one for each child), you need 6 separate circuits. I'd try getting a 5,500 watt (note that they run in the range 5,000-5,760 watts) installed, then supplement it with a single 1,500 watt heater to get up to around the 7,000 watts you were originally targeting.
Make sure you insulate that garage door. Air sealing is a good thing too, but those garage doors aren't usually insulated much if at all. You can get kits for this purpose that consist of multiple rigid foam panels cut to fit the door sections. You can also just tape the same rigid foam board up that you were planning on for the ceiling.
我再次提到你可能在这里有一些火灾代码，这种方式是这种方式的绝缘。刚性泡沫通常需要热或点火屏障（通常是干墙，但是钢板和硬盘也可以在某些情况下使用这样的露天面。我特别关注这种空间中的多个空间加热器和儿童。永久安装的单个更大的加热器比多个小型更安全。
And another warning: do NOT use typical extension cords with heaters running for long periods. You need the flat "air conditioner" cords in 14 gauge for this, or the heavier 14 and 12 gauge extension cords. Do NOT use the small two-conductor 16 gauge homeowner cords here, they will get hot and are very risky.
*** Think SAFETY FIRST, not COST.***
Bill
Thanks for the reply. Unfortunately in order to run a single large heater, such as the 7,500W heater we were looking at, the electrical in the garage would need to be updated. It’s not my home, but my kids are there, so I don’t know all the specifics, but I believe the house is 100amps and the garage is probably 40-60amps I think. The cost to upgrade was ~$3,700 and that is if the underground conduit (it is an old steel pipe) is still able to have wires fished through. Excavation was anothe 3k, which I think is absurd, but that is beside the point. Overall, we are trying to have our kids stay warm and be educated. We are not in Boston proper, just outside the city a few miles. I hear you on the fire code and I appreciate the concern, we’re just trying to do something temporary and within reason within a garage without spending thousands of dollars that the home owners are not really able to spend.
Is there a circuit breaker panel in the garage? If not, it's unlikely you have more than 20 amps at 120v. That would limit you to one 1500 watt heater.
是的，车库中有一个子面板，在那里有四个断路器。
[edit- it looks like Bill beat me to the punch as I was typing away. :-) ]
>"The suggestion was to decrease the volume of the space we are heating by getting 1″ 4×8 sheets of foil faced rigid insulation and laying them across the chords creating a ceiling "
Any foam board would need half-inch gypsum board or similar between the foam and occupied space for fire safety. You MIGHT be able to get away with a fire rated foam board (eg Dow Thermax) if it were simply storage space or a basement, but probably not for a 6 kid classroom.
The amount of heat going out of 500 square feet of R13 - R19 batt-insulated ceiling is about the same (or even less than) the losses from the fifty square feet of air-leaky antique single panes. Reducing that to only 350 square feet with foam board ceiling isn't the best bang/buck. Concentrate on improving the windows plus air sealing the building as a whole.
根据门设计，可以通过Cut'n'鹅卵石的火灾额定温泉，从而使车库门绝缘的良好的Bang / Buck，并为那些门升级挡风雨条。
临时situation, air sealing the antique windows with caulks & tapes then using purpose made shrink-wrap type window treatments for the second is cheaper than cutting interior storm windows out of plexiglass. The windows are a fairly standard size- you may be able to find some surplus-new or used triple-track clear glass exterior storms on craigslist for cheap (or free), which would cut the window losses in half on a more permanent basis, and protect the antique windows. As a DIY even new custom-sized clear glass (not low-E) storms would run about $400 for a set of five at box-store pricing, which is cheaper and more impactful than a 350 square feet of 1" polyiso foam-board ceiling even if going with cheaper, non fire-rated stuff.
If you still want to do something about the ceiling, 500 square foot rolls of PERFORATED (about 5 perms, not a vapor barrier) radiant barrier are about $70 at box stores, and don't have a fire rating issue. Supported by 16-24" o.c. strapping mounted perpendicular to the truss chords the radiant barrier would be able to support R13-R30 batts, potentially available for cheap or free on craigslist.
除非您需要在仅一个小时左右的时间左右，否则您并不真正需要7500WATT / 25,000 BTU / HR加热器。随着窗户治疗，您可能在户外30F（1月份波士顿的平均温度大约是6000 BTU / HR的负荷约为6000 BTU / HR），68F在室内。六个坐着的孩子和一位常设成人总共大约2000年BTU / HR，或600瓦，这并非没有任何东西，你可能会使用100-200瓦的荧光灯或LED灯21400 BTU/ HR的热量输入。在阳光灿烂的日子里，你甚至可以获得一些太阳能收益。
If you had a DIY-able 115V 1 ton mini-split (with pre-charged linesets) can be DIYed for about a grand, and can work on a standard 15A circuit with margin to spare. Most are capable of delivering 12,000 BTU/hr @ +17F,even more at higher temps, and would probably pay for itself in electricity savings in one winter compared to resistance space heaters. I doubt Boston is going to get to in-class publication education before next spring, given current COVID trends in the Bay State:
https://www.mass.gov/info-details/community-level-covid-19-data-reporting.
Thanks for the reply and all of the info - the mini-split option sounds interesting. As I mentioned, we are trying to not spend a lot of money for something that is temporary AND will simply just go back to a 2 car detached garage whenever this pandemic is over. Any foam insulation is temporary and we are not trying to legally convert this garage into living space, but I do appreciate the concern for what is code and what is safe, especially the information regarding the electrical. As I mentioned in my original post, the electrical would need to be updated in order to bring 240v out to the garage and update the panel. The estimate to do that was VERY expensive $3,700 and that is if they are able to use the existing conduit running to the garage. As you mentioned, two of the big problems I believe we need to address are the windows and the garage doors and hopefully air sealing them and insulating the garage doors will help.
>"...the mini-split option sounds interesting."
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>" ...the electrical would need to be updated in order to bring 240v out to the garage and update the panel. The estimate to do that was VERY expensive $3,700 and that is if they are able to use the existing conduit running to the garage. "
这就是为什么廉价110V DIY迷你分裂有一种感觉。目前市场上的大多数都是重新品牌（先锋，森佛尔，Mr.Cool，Gree等）Midea Units，与东芝压缩机。（MIDEA是世界上最大的AC设备制造商，吞噬了他们的大部分中国竞争。所有承运人品牌迷你分裂也是MIDEA。）一定要获得110-120VAC模型 - 它们都有几乎相同的版本在208-230VAC中设置了类似的部件号。
I mis-spoke on my prior post- most of the 115V one ton units need/want a 30A breaker, not 15A, and #10/3 wire. (Though in practice a 1-ton 115V mini-split usually won't trip a 15A breaker under normal circumstances.) The 3/4 tonners (which would also handle the load) need/want a 25A breaker and #12/3 wire. As long as the feed to the sub-panel can handle at least 30A it'll be fine.
While it pays to watch a few installation videos (YouTube has many) and read the manual, there is nothing too technical about installing them. Typical internet pricing for a 1-ton is about $800 + shipping (often free shipping) which includes a 16' or 25' pre-charged line set, with modest upcharges for longer refrigerant lines. In Boston bracket-mounting the compressor unit on the wall, on a side protected by roof overhangs is usually best. Leave 2' or more of clearance below to keep it above snow drifts. (In Worcester make that 4'.) A mounting bracket & line-set hide/conduit and some wire & breaker make up the remainder of the cost- it's a few hundred, not five. It's an afternoon project for a reasonably handy person (with an occasional helper to lift things) who has done it at least once, maybe a full weekend day for a first times. If you screw up big time and lose a bunch of the refrigerant charge any reasonable AC contractor would be able pump it down and re-charge for under $500.
通常有多余的行集,必须是有限公司iled up, since it's not a DIY to cut them to length and re-charged line sets. While many do fine coiling up and leaning the excess line pretty much vertically against the wall, in some cases that can create a vapor-lock problem with liquids collecting in the bottom of the loop on the suction line. It's better to place the excess line coil horizontal than vertical, avoiding the vapor-lock risk.
Safety must be you first priority the windows sound large enough to qualify as an emergency exit if they still operate freely and are low enough. If you cover them with rigid plastic they can no longer be used. I would cover the windows with thin film like the one in this link.
https://www.lowes.com/pd/duck-max-trength-7-ft-w-x-10-ft-l-clear-heat-control-window-film/1000344127
It is very very unlikely the electric service to the garage is adequate to heat the garage with resistance heat plus lighting and several outlets for the computers. My guess is two 240 volt 15 amp circuit is required for heating and two 120 volt 20 amp circuit one for lighting and a separate circuit for the outlets will be required.
Two heaters like the one in this link hard wired and attached to the wall would be much safer than portables that can be knocked over.
https://www.lowes.com/pd/fahrenheat-72-in-240-volt-1500-watt-标准 - 电动机板
了解电加热器是非常昂贵的operate even with low electric rates. From what I understand you are likely to have some of the highest rate in the US.
If we guess it will take 1 1500 watt heater running 24 7 to keep the garage warm. 1.5 kw per hour x 24 hours x 30 days with an electric rate of .20 per kwh = $216 per month
Safety says no exposed foam and no extension cords allowed.
Walta
I had similar service power limits for my wife's studio and ended going with a mini split for heat. Best decision ever.
不仅可以更便宜地运行而不是抵抗热量，在夏季时间更快地加热地点和交流。
Is there a natural gas service? I don't link combustion appliances, but a garage heater would deliver a lot of BTUs for not much money (if a gas line is already present).
Unfortunately there is no gas running to the house or the garage.
或bottled propane? According to Dana's calculations above something like this would be overkill:https://www.northerntool.com/shop/tools/product_25606_25606
It was the smallest I could find in a quick search. It is vented and installed which I think is the minimum you would want for safety (as opposed to ventless portable heaters).
A gallon of propane is around 90,000 BTU's. At a maximum load of 4,000 BTU's per hour (per Dana's calculation) a 5-gallon tank would last 100 hours. That's probably the cheapest way to get through the winter.
I would avoid non-vented gas-fired heaters in a small, enclosed space like this. Personally, I'm not a fan of non-vented appliances in general.
假设车库具有足够的电容，电阻加热器可能具有最低安装的成本。恒定的电阻热量昂贵。一个迷人的跑步将是一个更便宜的运行，并且每BTU的电力量较少，因为它基本上从户外泵送了一些热能，而不是从头开始制作所有热量输出。
Note that if the garage feed is a 40A, 240V circuit, that's 9.6kw peak, but a little less than 8kw for a heater since you don't want the heater to exceed 80% of the supply circuit capacity. You'd probably be able to get a 5kw heater to run on that circuit and still have enough capacity left over for some lights and computers. A 60A, 240V circuit is good for 14.4kw peak, or a little over 11kw worth of heater.
It's also worth mentioning that 6 separate typical 1.5kw space heaters is still 9kw. If you don't have sufficient electrical capacity for a 7.5kw heater, you won't have enough capacity for 7.5kw worth of smaller heaters, either.
Bill
我挂钩的加热器发泄。
I looked a little closer (I read the manual) for the heater at that link. It DOES mention a vent, but it’s not really a ducted system. It basically has a vent that gets mounted in the wall near the heater. There is no ducted exhaust to vent combustion byproducts to the outdoors.
Bill
While definitely not ideal, combustion heaters coupled with redundant CO detectors can be done safely. There would always need to be competent adult supervisions of course.
I get the feel that there isn’t someone with the experience around to install a mini split, otherwise the electricity wouldn’t be a limitation. I spent several years in an old farmhouse heated by butane/propane/kerosene, whatever I could get cheapest at the time.
Installing a mini split is something that could be done by myself. The problem, as I have written above, is that it’s not my home and I am not familiar with the electric there. There is a sub panel in the garage, but I think the amps out there are limited. For example, a circuit for an outlet on the outside of the garage kept tripping when a small pancake compressor and job site table saw were running. I just don’t think there is enough juice out there for an uptick in load without sinking money into a garage that will not be living space after COVID.
Probably worth verifying the amps then, but if there aren’t enough, is the home too far away to pull a length of 10 gauge wire? If it’s just temporary, could even be pulled through conduit above ground.
If the sub panel in the garage is fed from a main panel there should be a breaker at the main panel that shuts it off, that will tell you the ultimate capacity of the sub panel. If that breaker has two legs then it's a 240V circuit.
德克里主克has the right idea here: check the ampacity of the feeder supplying the subpanel in the garage. Since there is a subpanel, you ALMOST surely have 240 volts out there already. A quick conversion is as follows (adjusted for the 80% rule):
20A breaker: 3.84kw
30A breaker: 5.76kw
40A断路器：7.68kW
50断路器:9.6千瓦
60A断路器：11.52kW
If you have a double pole (usually this means two handles with a tiebar between them, but sometimes there is one handle with a breaker twice as wide), you have 240 volts going out there. If you have a single pole breaker (one handle, and not twice as wide as the others), then you only have 120v service which halves all those wattage numbers. Note that all the same numbers apply if you have a fused feeder (instead of a circuit breaker) too.
Assuming you don't have any huge loads out there, a 40A or larger will let you run a typical 5kw heater, and even have a little leftover for lights and computers.
如果具有压缩机的侧面插座，则可能意味着特定的分支电路超载而不是整个子螺母。在子板上是一个断路器的旅行，这意味着它是一个分支电路问题，或者在房子里做了一个破碎机喂养子蛋白之旅？检查的另一件事是240V系统的腿之间的平衡。例如，如果您有三个1,500瓦的空间加热器，以及30A，240V供应到子板，如果所有三个加热器插入到240V电路的相同“侧面”，则可能会跳闸30A断路器（其总共37.5安培）。如果您刚刚将三个加热器中的一个移动到另一个“侧”，则您只有25个放大的侧面，另一侧只有25个放大器，另一个放大器12.5安培，您就可以了。这是你可能检查的另一个简单的事情。随着不平衡的问题，您通常可以通过感受断路器的脸部来讲述。在双极断路器上，如果一侧看起来明显比另一侧温暖，你可能有一个不平衡的问题。
Bill
Something like this?
https://www.homedepot.com/p/Rinnai-EnergySaver-20-700-BTU-Vented-Propane-Furnace-EX22CTWP/306653491