A/C & Heat For 2 Car - Mini Split?

[001jigsaw]

Hey everyone!

I'm excited to have finally registered here, because that means.. work is finally underway!

So a little background - I am an automotive detailer on Long Island (Nassau, NY) and I run my business here at home. I typically average one car a week, which translates to 12-18 hours work time inside the garage over the course of 2-3 days. All of the wet stuff gets done in the driveway, and the rest inside the garage - once the car is in there, the garage door stays shut until I am finished. I want to reinvest a little into the business by upgrading the garage a bit. First thing I'd like to do is get A/C and heat in there. During May through September, the inside of the garage can get to be 85* F and quite humid. During the winter, I'd say it doesn't drop below freezing, maybe 40* F or so. A/C would keep me from nearly dropping to the floor during the hot months, and heat will immediately extend my working season. I'm not set on a Mini Split, but I figured it'd be the best option. The other obvious option would be a window unit for the A/C, but I don't know what I would do for heat. I can't have any type of propane or oil heater in the garage as there are food products in the garage for another business.

The garage:

• 22 ft x 22 ft (484 sq ft)
• Small attic up top. Did not measure height, I'm 6 ft and can't stand at the peak
• 8 Foot Ceiling - single 4 ft x 4 ft hole to access attic - no insulation in cavity between ceiling and attic flooring
• R13 in walls (pretty sure)
• Concrete slab floor
• One 32" x 48" two pane window, wood frame, west wall
• One 31.5" x 80" Metal door, no storm, west wall
• Garage door - 16 ft x 8 ft - Vinyl (polyethylene?)

I was thinking a 12,000 BTU unit (lowest) and that a 15,000 BTU unit would probably be best. If I can keep the temps in there around 70, while keeping the humidity down, I'll be super happy. During winter, 60* is fine. I'm usually in there when it's 40* with a couple sweatshirts on, so being able to be in there in the middle of February with just a light sweatshirt on will be perfectly fine, I'm not looking for it to be toasty warm, just not frigid.

What do you guys recommend? I'm all ears! I have quite a few friends (myself included) who are quite handy, and I have two electricians in the family, so i was planning on installing it myself. Although recently I heard from a buddy that it's best to keep a vacuum on these mini splits for a period of time, and fill them in a certain way rather than simply unboxing it and hooking up the lines for a pre-filled unit. I'm not too knowledgeable about all that, so please tell me what you guys think.

Looking for recommendations on specific units as well. I'm not loaded with cash, I'm really just looking for a good economical mini split to provide comfortable working conditions.

Oh, also.. would it be beneficial to install an exhaust fan up in roof in the attic?

Thanks in advance everyone!

 

[justinjoyal]

What kind of insulation in the roof ? This will greatly affect sizing.

A mini-split would perfectly suit your needs.

 

[001jigsaw]

What kind of insulation in the roof ? This will greatly affect sizing.

A mini-split would perfectly suit your needs.

Looking up into the attic, I see wood under the roof, no insulation

 

[stm317]

Upstate NY, and no insulation in the ceiling or attic? That's going to cost you a fortune to heat/cool. At a minimum, I think I'd fill the cavity between the ceiling and attic floor with the insulation of your choice. I'd try and find or fab an attic door to keep some of the heat from rising.

 

[theoldwizard1]

Upstate NY, and no insulation in the ceiling or attic? That's going to cost you a fortune to heat/cool.

Yep !

You need a ceiling and about 12" of insulation. Then a good, low temperature heat pump. It is a waste of money without the insulation.

 

[001jigsaw]

Upstate NY, and no insulation in the ceiling or attic? That's going to cost you a fortune to heat/cool. At a minimum, I think I'd fill the cavity between the ceiling and attic floor with the insulation of your choice. I'd try and find or fab an attic door to keep some of the heat from rising.

Yep !

You need a ceiling and about 12" of insulation. Then a good, low temperature heat pump. It is a waste of money without the insulation.

I'm not upstate, I'm on Long Island near JFK airport - but I see your point lol. My grandfather built the garage years ago, it would appear he never finished or changed his mind, because there's two big rolls of R-19 fiberglass up in the attic. was planning on putting an attic door to block it off. The access hole is hacked up, I don't know who the heck cut it - perhaps whoever installed the garage door motor after my grandfather passed. The hole roughly measures 41" x 38"


I assume either the ceiling would have to come down or the attic floor would have to come up (which isn't even screwed in) in order to put the insulation in the cavity. I care far more about cooling down the garage than I do heating it.

What do you guys recommend?

 

[themiller]

You need to fix the attic insulation and button that hole up. No 15k unit will be able to keep up with the heat (or cooling) loss. Get everything out of the attic, pull up the floor, insulate to R49 or 60. That's step 1.

I assume you have 220 in the garage? If so - I'd suggest buying a dedicated 5,000 watt electric heater with thermostat instead of relying on a heat strip in a split unit.

I'd mount an A/C unit through the wall as it will be less expensive than a split-unit and easier to install IMO.

You can get a 20k BTU AC unit for <$550 and install it yourself quite easily.

Same with the heater - here's one for $120.

https://www.amazon.com/dp/B009F1SWH8/?tag=atomicindus08-20

 

[thickhead]

I agree you have to insulate and seal it up first. In my insulated 24x24 just north of you in CT, a 12k window unit and a 6kw electric heater are more than enough to be comfortable year round.

 

[stm317]

If you don't want to pull up the attic floor, insulation can be blown into the cavity by drilling holes in the floor instead. Although pulling up the floor would probably get you a better end result.
Blown cellulose has an R value of 3.5 per inch of depth, so depending on the size of your framing, you could easily end up with R21 or higher in the ceiling just by filling the cavity.

The utilities in your garage will dictate some of your options for HVAC too. Do you have 220V electric or just 110? Are Natural gas or propane available? Cooling is going to be done electrically, but if you can heat with gas instead of electric, it can really save you money. It may be cheaper (initially and/or long term) to have a hanging gas furnace and a wall mount AC than to run a mini split year round. Just depends on tons of factors (insulation, utility rates, desired temps, etc).

 

[justinjoyal]

You need to fix the attic insulation and button that hole up. No 15k unit will be able to keep up with the heat (or cooling) loss. Get everything out of the attic, pull up the floor, insulate to R49 or 60. That's step 1.

I assume you have 220 in the garage? If so - I'd suggest buying a dedicated 5,000 watt electric heater with thermostat instead of relying on a heat strip in a split unit.

I'd mount an A/C unit through the wall as it will be less expensive than a split-unit and easier to install IMO.

You can get a 20k BTU AC unit for <$550 and install it yourself quite easily.

I agree that ceiling insulation has to be adressed first. At least R20, but the more the better.


Now:


There is no heat strip in a mini-split.

Through the wall units are less efficient, noisier and require a huge hole cut into the wall. I’m not a fan.

The utilities in your garage will dictate some of your options for HVAC too. Do you have 220V electric or just 110? Are Natural gas or propane available? Cooling is going to be done electrically, but if you can heat with gas instead of electric, it can really save you money. It may be cheaper (initially and/or long term) to have a hanging gas furnace and a wall mount AC than to run a mini split year round. Just depends on tons of factors (insulation, utility rates, desired temps, etc).

OP specified no propane or oil in his original post. I assume no gas either ? He’s gotta go electric.

 

[001jigsaw]

Thanks for the replies fellas.

Yes, I have 220 out in the garage. There are no gas lines currently ran.

The easiest thing for me to do would be to remove everything from the attic, lift up the floor boards (they aren't secured, just laid down) and stuff it with insulation like you guys mentioned. What size insulation do you guys recommend? I see the suggestion for 49 or 60.

As for wall unit A/C - Why not use a window unit since I have a window, instead of putting a huge hole in the wall? Also, although a wall/window unit may initially be cheaper, aren't they much less efficient?

Another family member of mine owns a food delivery business and stores dry goods in the garage, that is why I cannot use oil or propane. As for gas, I suppose it would be okay, considering that's the same method used to heat homes. I'd have to check, as that is my relative's main concern with anything I do in the garage.

 

[mike93lx]

Thanks for the replies fellas.

Yes, I have 220 out in the garage. There are no gas lines currently ran.

The easiest thing for me to do would be to remove everything from the attic, lift up the floor boards (they aren't secured, just laid down) and stuff it with insulation like you guys mentioned. What size insulation do you guys recommend? I see the suggestion for 49 or 60.

As for wall unit A/C - Why not use a window unit since I have a window, instead of putting a huge hole in the wall? Also, although a wall/window unit may initially be cheaper, aren't they much less efficient?

Another family member of mine owns a food delivery business and stores dry goods in the garage, that is why I cannot use oil or propane. As for gas, I suppose it would be okay, considering that's the same method used to heat homes. I'd have to check, as that is my relative's main concern with anything I do in the garage.

Don't stuff in Fiberglas insulation. If you compress it, it becomes much less effective. Figure out what height you need to blow in cellulose ate-40 to r-60 and then make that happen. I'd forget about doing this with batts.

 

[001jigsaw]

Don't stuff in Fiberglas insulation. If you compress it, it becomes much less effective. Figure out what height you need to blow in cellulose ate-40 to r-60 and then make that happen. I'd forget about doing this with batts.

Thanks, I'll look into it. Any idea how much that might cost? I remember hearing things 5 or so years ago about that stuff bothering people's respiratory systems - any issues with that?

 

[stm317]

Cellulose is about R3.5 per inch of depth. You'd need 11.5 inches deep to get R40 and over 17 inches to hit R60. Unless there's some crazy thick framing in the ceiling, either of those would make your attic useless. That may or may not be acceptable to you.

Honestly, for a garage that you're only trying to keep the worst of the chill off, R40-60 is probably overkill. Those R value suggestions are more for living space than a garage. They'd be great, and would allow your HVAC to operate at its highest efficiency, but is it worth the extra money and losing your attic space for a slight bump in efficiency and comfort for the time that you'll be out there? Only you can really decide that.

 

[OzarkMan]

Consider spray foaming the underside of the roof and keep your attic space for storage. Makes the whole thing a conditioned space.

 

[themiller]

Thanks, I'll look into it. Any idea how much that might cost? I remember hearing things 5 or so years ago about that stuff bothering people's respiratory systems - any issues with that?

I got 1100 sq ft blown in to r60 for <1k a few years ago and that included the ventilation baffles extended to the eaves. I imagine with inflation it’ll be right around 1k for you paying someone else to do it. Wasn’t any cheaper to rent the unit and buy the supplies to DIY. Wasn't really any cheaper to do less either. I think the guy wanted $100 to go from somewhere in the r30's to 49, and another $100 or so to go all the way to 60. I got up there with a tape measure to check. Furnace and A/C in that house only ran on the coldest and hottest of days afterwards. 1950's midwest house.

Your labor to remove attic boards and close up hole. Insulate the back of the access board with the fiberglass stuff you have.

You will notice a huge difference.

As for putting it in a window - sure! That would be even easier. I didn't see a window in your pictures, or specs.

 

[LifeLongWNYer]

Hi, Jim, here in Western NY. Just like I do not know know the geography of many states in the US, I understand that many non-NYers don't understand the geography of NY. Heck, even a lot of NYC people say "upstate" is anything north of Rockland County.

I would gladly trade my winters here, for those in 001JigSaw's Nassau County. I get about 110" more inches of snow than he does, and the temperatures here average 30 degrees colder than he gets on Long Island.

 

[Ohmthis]

OP, got some questions that I don’t believe you’ve answered. Do you use the attic for storage? Is it required, I.E. you can’t loose that space for storage? Will this hvac be running all year or just when you are out there? It sounds like you are a good candidate for a mini split heat pump. Depending on manufacturer and models, they can heat down to -15 or so. Most other types loose efficiency down around 15-20*. The more you insulate and seal any openings where air can get in, the better the hvac will work no matter which type you use. Also, it’s cheaper to insulate now then later and will pay for itself over a time period.
If you need the attic for storage, then pull the boards up and fill the void with a blown in cellulose or fiberglass. Either of those will help seal against air infiltration and provide a good r value. If you don’t need the attic for storage, remove the floor and blow in a cellulose or fiberglass to an R30-R38. A mini split is designed to be run continuously. They can’t recoup/catch up well if they are asked to drop or rise a temp quickly. They can be very efficient and make an area very comfy. I install Mitsubishi, but wouldn’t scoff at a Fujitsu or daikin. These are generally looked at as the top three in no particular order. I wouldn’t go any bigger than the 15,000 btu you are mentioning if you seal and insulate the ceiling properly. Hope this helps.

 

[Fueler]

What they said. Insulation first, minisplit second.
You can thank us later.

and no whining if you disregard the majority advice.

 

[001jigsaw]

Thank you for your responses everyone, you've been a great help. I'm currently in the process of taking everything out of the attic, throwing away the junk, scrapping the rest, and finding some cool stuff my grandfather left. Found an old WW2 gas mask! I'm still a bit of a ways away before I can start on the insulation - I have to patch in some drywall in a few spots on the ceiling, and figure out what I'm going to do with that access hole. I didn't realize attic ladders are ~$200. I'd make one myself, but I haven't been able to find the spring hinges anywhere. Anybody have any ideas for a way to get up there that would still seal off the hole? Maybe some kind of access panel that I can lift up, or swing down, and then just use a regular ladder like i've been doing? I don't go up there often.

Yes, the attic will continue to be used as storage.

OP, got some questions that I don’t believe you’ve answered. Do you use the attic for storage? Is it required, I.E. you can’t loose that space for storage? Will this hvac be running all year or just when you are out there? It sounds like you are a good candidate for a mini split heat pump. Depending on manufacturer and models, they can heat down to -15 or so. Most other types loose efficiency down around 15-20*. The more you insulate and seal any openings where air can get in, the better the hvac will work no matter which type you use. Also, it’s cheaper to insulate now then later and will pay for itself over a time period.
If you need the attic for storage, then pull the boards up and fill the void with a blown in cellulose or fiberglass. Either of those will help seal against air infiltration and provide a good r value. If you don’t need the attic for storage, remove the floor and blow in a cellulose or fiberglass to an R30-R38. A mini split is designed to be run continuously. They can’t recoup/catch up well if they are asked to drop or rise a temp quickly. They can be very efficient and make an area very comfy. I install Mitsubishi, but wouldn’t scoff at a Fujitsu or daikin. These are generally looked at as the top three in no particular order. I wouldn’t go any bigger than the 15,000 btu you are mentioning if you seal and insulate the ceiling properly. Hope this helps.

Yes, I need to keep the floors up there. The HVAC will only be used while I am out there, which would at most be a few days a week. I'm leaning towards a 240v window unit and a forced air heater because of the recoup time.

 

[u3b3rg33k]

Thank you for your responses everyone, you've been a great help. I'm currently in the process of taking everything out of the attic, throwing away the junk, scrapping the rest, and finding some cool stuff my grandfather left. Found an old WW2 gas mask! I'm still a bit of a ways away before I can start on the insulation - I have to patch in some drywall in a few spots on the ceiling, and figure out what I'm going to do with that access hole. I didn't realize attic ladders are ~$200. I'd make one myself, but I haven't been able to find the spring hinges anywhere. Anybody have any ideas for a way to get up there that would still seal off the hole? Maybe some kind of access panel that I can lift up, or swing down, and then just use a regular ladder like i've been doing? I don't go up there often.

Yes, the attic will continue to be used as storage.



Yes, I need to keep the floors up there. The HVAC will only be used while I am out there, which would at most be a few days a week. I'm leaning towards a 240v window unit and a forced air heater because of the recoup time.

perhaps consider a 240V window unit with heat (some even have reversing valves so you get cheap heat over 40F) ? i'd lean toward the minisplit because with resistance heat, operating cost will rapidly eclipse purchase cost.

I have a FFRH0822R1 slide-in window unit that says it cools at 8k, heats at 7k above 40F (reversing valve), and below 40F it heats at 3.5k. 120V unit. I'm currently hacking the controls out and replacing with new ones to use it for my garage year round (no defrost control from the factory).