I currently have an 18k mini split in the garage. It was here when we bought the house in 2020. Date on it is 2005, brand is NSP. Garage is 825 sq feet, 9' ceiling. attic has insulation doors are insulated, the 2 ( more like 1-1/2) exterior walls are not. Im in AZ and yesterday, it took 5 hours to drop the temp from 92 to 86. When its 100 in the garage I cant get it below 90 in that time. I only put the AC on when im working in there. SO, my questions are: Do I need a larger unit? Will insulating the 2 walls make a noticeable difference? Should I do I DIY setup, because the electric is already run?
Do I need a new or bigger Mini Split
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bornbadbob
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I would do the insulation first, just insulating my garage door made a huge difference
With all the heat soak, you’re asking a lot of your AC to drop the temp that fast.
During the summer months (Mesa, Az), I’ve long gotten into the habit of turning on the mini split the night before I’ll be working in the garage and let it run through my weekend. That’s been the only way to keep it comfortable.
I’d give that a shot before getting a larger unit.
During the summer months (Mesa, Az), I’ve long gotten into the habit of turning on the mini split the night before I’ll be working in the garage and let it run through my weekend. That’s been the only way to keep it comfortable.
I’d give that a shot before getting a larger unit.
ericm
Well-known member
Mini splits need to be on all the time. They don't have the excess capacity to heat or cool a space quickly.
Air sealing and insulating the uninsulated walls will help the unit keep the space cool.
Mini splits have improved a lot in the last 10 years. You can probably get one that is more efficient than the current unit. But that will just mean that it costs less to run, not that it cools significantly faster. To do that you'd need a larger unit which would likely require new wiring to support it. Bigger units draw more power.
aggie113
Well-known member
Keep in mind that default programing for most minisplits is running quiet vs max performance. If you leave the blower speed set to the default of Auto it may ramp up for a larger temp change but I would set it manually to it's highest speed to maximize performance. Also, take a look at the state of the interior/exterior units and make sure things are clean. In my garage, even with regular cleaning of the 'filter', it does a poor job of keeping the blower wheel clean. I bought a kit off Amazon that includes a bib and a low power electric power washer to clean the gunk off the blower. You can also use it to spray down the fins.
In my 30x40x18 garage I'm in the process of adding a second minisplit. The exiting 2ton unit has trouble keeping the insulated garage at 80 during the summer and adding a second unit should resolve that and also allow me to bring temps down quickly when having to bring a hot car into the garage during the afternoon.
In my 30x40x18 garage I'm in the process of adding a second minisplit. The exiting 2ton unit has trouble keeping the insulated garage at 80 during the summer and adding a second unit should resolve that and also allow me to bring temps down quickly when having to bring a hot car into the garage during the afternoon.
rlitman
Well-known member
Insulation is pretty much always the first answer, though in a garage, air sealing the door gets top priority.
Are the exterior walls bare stud (easy to insulate)? What sort of attic insulation are we talking about? Which way do the exterior walls face (are they getting lots of sun, or not)?
One thought is that an aluminized reflective radiant barrier could be added in the attic, or perhaps even the ceiling and inside of the exterior walls and garage door, and that can cut down quite a bit on heat radiating in from the heat soaked walls.
dcg9381
Well-known member
18k BTU in 900 sqft? I'd say that's a lot of AC. I've got less per sqft in the shop and it's moderately insulated with 3 x 14x14 roll-up doors that are not insulated and leak like crazy.
I over AC (ductless) spaces that are not well insulated all the time. For exactly the reason you stated - I don't want to have to cool them 24/7.
With the OP, I'd start with inlet and outlet temperatures to determine if the unit is performing appropriately.
More insulation is always better, but most heat loss / gain is going up...
mike93lx
ALLIANCE MEMBER
Insulate, air seal and then keep the mini running.
How well insulated is the ceiling?
How well insulated is the ceiling?
I'll add to that. The brand I have used has a setting to change the default to a max cooling rate, temporarily. It runs the condensor and evaporator fans at max. Makes a huge difference. Maybe check your brand's web site or manual if you have it.
But more insulation and air sealing is always a good thing.
mike93lx
ALLIANCE MEMBER
Like most things, there is a point of diminishing returns. You can easily spend more on insulation than would be saved back in a reasonable amount of time
dcg9381
Well-known member
Recommended insulation is based on full time heating/cooling. There is definitely a "middle ground" if you're not heating/cooling 24/7. Minis are good about being able to "over BTU" because they can don't just run flat out all the time.
kngelv
Well-known member
I think 24K would be better. Yes insulate the walls and double check your ceiling insulation and door seals. As others have said you need to leave it running as opposed to turning it up an hour before you go out there.
James
James
fitter30
Well-known member
Air is easy to do. Mass is hard. Have a lot of stuff, hot car these are all mass.
OK, here's some more info and answers:
Garage is 29x29x9
Attic has 6" blown insulation ( the house attic has only insulation on the "pitch" none on the "floor")
Garage doors face N-N/W (ill call it N for simplicity)
East wall is uninsulated, no shading.
West wall is also uninsulated, with 24' of floor to ceiling 2' deep cabinets (5' backs to an interior room)
South wall backs to the house, im unsure if its insulted but most likely it is. Its a firewall and has wood (chip board) and drywall.
Garage and house attics are not open to each other
Garage walls are finished, drywall, so not easy to insulate, especially the west wall with the cabinets
AC is on a 40 amp breaker
model number S240a-19k10
seer 10.2
Outlet temp this morning outside temp 80 outlet temp 60-65 (i dont have an infared temp gun, using vent gauge. IIRC, same outlet temps when it was over 100 outside
Garage is 29x29x9
Attic has 6" blown insulation ( the house attic has only insulation on the "pitch" none on the "floor")
Garage doors face N-N/W (ill call it N for simplicity)
East wall is uninsulated, no shading.
West wall is also uninsulated, with 24' of floor to ceiling 2' deep cabinets (5' backs to an interior room)
South wall backs to the house, im unsure if its insulted but most likely it is. Its a firewall and has wood (chip board) and drywall.
Garage and house attics are not open to each other
Garage walls are finished, drywall, so not easy to insulate, especially the west wall with the cabinets
AC is on a 40 amp breaker
model number S240a-19k10
seer 10.2
Outlet temp this morning outside temp 80 outlet temp 60-65 (i dont have an infared temp gun, using vent gauge. IIRC, same outlet temps when it was over 100 outside
I have a 24k in my 500sqft 2.5 car. insulation went up first because it's hard to put drywall behind a mini split.
I sized it for heating, but it cools plenty quick.
I used the app to program it to heat 62, cool 75, instead of the remote that'll let you set it at auto 72 (basically heat 71/cool72 - so silly). last month i paid $3.95 for power.
ask me once feb rolls around what I think vs my 6kW electric I ran last year.
You need to leave it on all the time. It will probably actually cost less to run it that way. My 24K in an uninsulated shop is cheaper to leave on, I tried it both ways. Once everything finally cools off completely it should be easy for it to maintain whatever temp you want and cheap to run.
dcg9381
Well-known member
I think that depends on how often you actually need to heat/cool the shop. If you're like me and only heat/cool 2-3 times a month, it's WAY cheaper to leave it off... But I'm running 48k BTU on 2400 sqft. I have no expectation that I can walk in there and cool it from 100 degrees to 80 in the summer in an hour. To me, there's not point in cooling a space that big if I'm going to be down there for an hour. If I've got a project and I'll be down there for a few hours, I'll heat/cool it.
YMMV. First thing I'd do is check the spread between intake air and output air temp. Difference should be at least 20 degrees. If it is, unit is working properly and you need a "bigger" unit to cool that space "faster" or you need to run it more to see if it'll hold temp. Or add wall insulation (which isn't my first go-to, might be cheaper to do a bigger unit).
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kngelv
Well-known member
I'm not trying to be negative but people come on here all the time asking questions hoping to avoid reality. Only you know how much you are willing to do or spend but there is no trick way for this. If you don't want to add insulation because it's inconvenient then you are going to waste a bunch of money and time with little benefit. You need to start with the facts and decide what to do from there:
1. You need to insulate. You are between R-13 and R-23 depending on what blown material is in your ceiling. You should have at least R-49.
2. Walls should be at least R-13. Two are uninsulated, one your not sure of and the door could be as low as R-5. Basically useless.
3. You are going to waste a ton of money if you don't insulate. A ton!
4. 18K is too small for your space.
5. Without insulation you will need a much larger mini-split running 24/7 to maintain a cooler temp and the efficiency will drop so much that a regular AC unit would be cheaper to run.
James
1. You need to insulate. You are between R-13 and R-23 depending on what blown material is in your ceiling. You should have at least R-49.
2. Walls should be at least R-13. Two are uninsulated, one your not sure of and the door could be as low as R-5. Basically useless.
3. You are going to waste a ton of money if you don't insulate. A ton!
4. 18K is too small for your space.
5. Without insulation you will need a much larger mini-split running 24/7 to maintain a cooler temp and the efficiency will drop so much that a regular AC unit would be cheaper to run.
James
>You need to leave it on all the time. It will probably actually cost less to run it that way. My 24K in an uninsulated shop is cheaper to leave on, I tried it both ways. Once everything finally cools off completely it should be easy for it to maintain whatever temp you want and cheap to run.<
Im not sure how that will save me money. I go weeks at a time without turning it on. I really only use it if I have a job to do. Last one was 2 weeks ago, next on is next weekend (just to give an example)
Im not sure how that will save me money. I go weeks at a time without turning it on. I really only use it if I have a job to do. Last one was 2 weeks ago, next on is next weekend (just to give an example)
How much and how difficult would insulating 2 walls already finished and 1 with built in cabinets?
Im not concerned with the wall that backs up to the house, even if its not insulated, which i really think it is.
I dont need it cooled 80% of the time, only for long projects (2 hrs or more) and 0% from Nov to March.
I wouldn't mind "wasting money" cooling it if its cheaper than insulating. Attic insulation is pretty straight forward, and I'll do this before next summer.
What is the minimum size I should have for this space? AND knowing what I have will I need to upsize the electrical?
2 times a month from May to October would be alot. probably never during the so called "winter" here
mike93lx
ALLIANCE MEMBER
You can use blown in with a finished wall, just need to drill a hole in each stud bay then it can be dense packed. I'd have an insulation contractor out to look at it
I used it today, mostly to see how my condensate line repair worked. The previous homeowner who installed it thought it was a good idea to have the line turn 90 deg. and run 8" sideways before turning 45 deg. down. Line broke, and I have temporarily fixed it. I tuned it on at 8am 90 outside, 92 inside. 6 hours later it was 86 inside. Had it on the max fan and temp set at 61 (lowest) Pretty much the only settings I can use to get max cooling. After shutting it off temp rose from 86 to 90 in 3 hours
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ericm
Well-known member
You might be able to improve it by turning it into a ventilated attic, with the insulation on the ceiling. The sun's heat beating down on the roof heats it to well above ambient. Then it heats up the air in the attic. Insulation just slows that down some. With the vented attic, the hot air inside will rise through the upper vents and cooler air will enter from the lower vents. You will also be reducing the volume that needs to be cooled. As it is now you're cooling the entire attic. I don't know if you need R50 in the attic but that does not cost much more than R38.
The wall that's against the house counts as insulated.
You can rip out the drywall, insulate and replace the drywall. Or cut holes and blow insulation in, then patch the holes. Unless you have texture on the drywall that needs to be matched, patching is pretty easy.
If you're going have long periods of time without using the space it's fine to turn it off. But you need to turn it on well before you want to use the space. How long depends on how hot it is and what temp you want it to be in there.
It's interesting that some posters on this thread say your mini split is too small and some say it's too big.
I ran a manual J with the info you have given, and it says that your existing unit should be plenty for your existing insulation. I may have done it wrong or not been given all the pertinent info or both. I assumed Phoenix which could be wrong. But Manual J says what BTUs you need to maintain a temperature (75 degrees) given 98% worst case outdoor temp, NOT how many BTUs you need to cool the space significantly in an hour or two when it's been heat soaking for days. You need way more BTUs for that.
I thought so.
I assumed that.
Id have to go with cutting holes.
Same here. from what I've read, its a good size for a regular living space. But i though too small for a poorly insulted garage. Especially for a space that's not cooled consistently.
THAT is my big question. what is WAY more BTUs?
And, seeing that the system is 20 years old, would a new unit work faster, or just more efficiently
dcg9381
Well-known member
Yea, dunno where you're at. 2021 we got "odd weather" and a week of below freezing.
I had the same theory (don't really need heat) until I did... Ended up adding propane.
Notgrownup
Well-known member
You will see such an improvement with insulation. I leave mine on 24/7/365 on AC I have it on 81 and on heat on 63 depending on season but I use it mostly to keep humidity down over on this side . I have a lot of exotic wood I keep and want it to stay tru for my woodworking projects.
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ericm
Well-known member
That's hard to calculate, in part because it's so vague. Worst case would be that you go in there in the late afternoon on a scorching day, turn on the A/C and expect it to cool down quickly. A/Cs don't work as well when its really hot outside and the inside is heat soaked. You need a whole **** ton of BTUs for that. Mini splits go up to 36k btus and I suspect that might not even be enough for that worst case.
That's a good question. For sure it would be more efficient at moderate temps. Very likely it will heat better at low temps. But more efficient cooling at high temps? I haven't looked into that. But it's certainly possible. You can find heating and cooling curves at https://ashp.neep.org/#!/product_list/ but it might only be for more recent units.
pima67
Well-known member
in our lovely dry heat, the non-shaded east and west walls receive mucho solar radiation, first in the morning and then in the afternoon. I would think that insulation in those walls would help immensely. If there is room, radiant barrier, as mentioned above, would also help. I had it installed in our attic, and it seems to be a big help. At least TEP rates our electrical usage in the summer as one of the lowest for this sized house.
I'm in phoenix area. If there's a week below freezing here, hell has frozen over
Already started looking into it. DIY vs. "professional install". I do it over the winter, if i DIY it
ericm
Well-known member
The quote I got for installing attic insulation in my shop is less than the cost of materials if I bought them at the local home store.
Same here! I had my attic blown in. I had priced the materials at $750. Then I needed to find a friend to abuse. Before I did it I got a quote to do it. The conversation with the insulation company was funny. They insisted they had to come and look at the attic. I told them it was a 1950's rambler, access near the middle of the house, he has probably seen hundreds of them, why do you need to come out?. Then he went on and said he needed to know how much insulation was up there now? I told him there wasn't much, assume none and he tells me about $800. I told him to go a head and do the job and if he uses less time and insulation, just charge me less. He did and I got a bill for $700.
I don't know why people have to make things so complicated!
That is kind of a simply incorrect statement!
With properly sided units you are probably better off to let them run all the time, but what if it is 80F versus 95F outside? Cloudy, or bright sun? If the unit cools at 95 is is basically over sized for a 80 degree day. Or what if the cooling load is 18K and the guy has a 24K installed? The 24K will cool the space down faster than an 18K. Standard AC or mini split, it doesn't make a difference. One thing nice about inverter mini splits is you can oversize them and they will ramp up or down to adjust for the cooling load, where a straight AC can not.
Stating they don't have the excess capacity can be applied to any properly sized AC unit. Excess capacity is a polite way to say you have an oversized unit.
The attic, I assume is the easy part. there's already 6" there too. Its the 2 exterior walls that I think will be more costly
rsanter
Well-known member
Insulation is a no-lose propistion. Start there
then if your unit is working fine I think I might look at adding a second unit that you just use to break the heat, then use one to maintain the temperature
then if your unit is working fine I think I might look at adding a second unit that you just use to break the heat, then use one to maintain the temperature
My Old Tools
Well-known member
I have a 36k MrCool in 1200sf. The building has 4" fiberglass metal building wrap plus another 8" on the roof. I have a bunch of windows on the north and east. 12x12 overhead door is insulated facing south. If i kick MrCool into Turbo mode, I can get it comfortable in 20 minutes. My unit sits 9 feet off the floor, everything above that gets a lot warmer.