1000 square foot garage in central TX

[Centex Hokie]

I am getting quotes for adding a mini split to my garage here in Central TX. It is pretty well insulated with R15 in the walls and R38 in the ceiling with a 9 foot ceiling, 2 insulated garage doors, one window and one outside door. One of the HVAC guys says I need a 2 ton system while another one says a 3 ton unit. Any suggestions?

It is hot here in the summer (20 days or so reach 100 with a lot of 90's between June and August), but the winters are mild with only a few days below freezing.

 

[strutaeng]

I am getting quotes for adding a mini split to my garage here in Central TX. It is pretty well insulated with R15 in the walls and R38 in the ceiling with a 9 foot ceiling, 2 insulated garage doors, one window and one outside door. One of the HVAC guys says I need a 2 ton system while another one says a 3 ton unit. Any suggestions?

It is hot here in the summer (20 days or so reach 100 with a lot of 90's between June and August), but the winters are mild with only a few days below freezing.

Need to do a manual J calculation to properly size. That's residential code-prescribed insulation you have there, i.e. plenty of insulation for a shop!

I would guess 2 tons are plenty. Probably 1.5 tons will work, depending on what you are doing. 3 tons is 333 sq ft per ton! That's insane! Maybe you are a blacksmith and have a forge in there? LOL Running car engines inside? Any additional source of heat gain?

 

[Centex Hokie]

I would guess 2 tons are plenty. Probably 1.5 tons will work, depending on what you are doing. 3 tons is 333 sq ft per ton! That's insane! Maybe you are a blacksmith and have a forge in there? LOL Running car engines inside? Any additional source of heat gain?

No, no other heat source. I was thinking that was too high.

 

[strutaeng]

No, no other heat source. I was thinking that was too high.

A little oversized with mini splits is okay, because they are variable speed and will not short-cycle like conventional split systems. So if you need, say, 1.5 t of cooling capacity and install a 2.0 t, then the mini-split only runs to cool 1.5 t capacity. On a conventional system, it would run 2.0 t while you need it or not.

The slight oversize capacity will help you cool down the space quickly, say after coming back from vacation. Still, 3t seems way out of wack.

I hope that makes sense.

 

[strutaeng]

No, no other heat source. I was thinking that was too high.

A little oversized with mini splits is okay, because they are variable speed and will not short-cycle like conventional split systems. So if you need, say, 1.5 t of cooling capacity and install a 2.0 t, then the mini-split only runs to cool 1.5 t capacity. On a conventional system, it would run 2.0 t while you need it or not.

The slight oversize capacity will help you cool down the space quickly, say after coming back from vacation. Still, 3t seems way out of wack.

I hope that makes sense.

Oops, double post

 

[Centex Hokie]

A little oversized with mini splits is okay, because they are variable speed and will not short-cycle like conventional split systems. So if you need, say, 1.5 t of cooling capacity and install a 2.0 t, then the mini-split only runs to cool 1.5 t capacity. On a conventional system, it would run 2.0 t while you need it or not.

The slight oversize capacity will help you cool down the space quickly, say after coming back from vacation. Still, 3t seems way out of wack.

I hope that makes sense.

Yes that makes sense. I will go with a 2 ton system.

 

[dcg9381]

I have a 2400 sqft garage. Same geography. R15 sides, R18 ceiling. Big roll-up doors (3) that are poorly insulated.
I'm running 2 x 24K BTU units. This works to knock down heat in the shop even on hot days. I'd say that if I was using every inch of this building, I'd probably add another unit for the high heat of summer. My units are concentrated on a living space area and I have no other means of air movement.

As mentioned above, oversize is OK. For some reason I found that 36k units were a different price point than 24k units - that's why I chose to run 2 x 24k

 

[Centex Hokie]

I have a 2400 sqft garage. Same geography. R15 sides, R18 ceiling. Big roll-up doors (3) that are poorly insulated.
I'm running 2 x 24K BTU units. This works to knock down heat in the shop even on hot days. I'd say that if I was using every inch of this building, I'd probably add another unit for the high heat of summer. My units are concentrated on a living space area and I have no other means of air movement.

As mentioned above, oversize is OK. For some reason I found that 36k units were a different price point than 24k units - that's why I chose to run 2 x 24k

Thanks. The guy who is proposing a 3 ton unit said he didn't think the price difference would be much. We'll see what he comes up with. It sounds like unless there is a small price difference that the 2 ton will be the way to go as your garage is a lot larger than mine. Thanks for the information.

 

[strutaeng]

Yes, that's a good point, although OP mentioned R38 insulation and 9' ceiling. That's some serious insulation, at least for a shop and this part of the country.

I've mentioned on other threads that I'm currently cooling an addition 22'x66'x17'high with a R19 fiberglass + 5" XPS walls and R38 fiberglass ceiling with a 22,000 BTU window AC. Set to and maintained 75F while it was 104F outside! Can't imagine OP having 36,000 BTU of heat gain.

The window AC was temporary. I just received my Mr. Cool Olympus 24kBTU that would get installed permanently...

OP: Maybe (2) 12,000 BTU units are also an option? Will obviously consume a bit more energy than a single 24,000, but will have more even temperature throughout the space.

 

[Centex Hokie]

I maybe doing a Mr Cool DIY. Quote for a Gree installed was $3,985.91 and for a Mitsubishi $4,824.00. The electrical is already done and I have a sink right under where the head unit is going for a drain. Can the drain on a Mr Cool DIY be separated to stay inside?

Thanks.

 

[dcg9381]

I haven't installed Mr. Cool, but they all seem to have separate condensate drain lines. They are designed to drain to the outside, but you can install pumps on them if gravity drain is problematic. In your case, as long as the P-trap of the sink is below the unit - you can make it work.

From experience, I don't like HVAC drains going into my plumbing. Myself and other people have had this eventually cause fairly frequent clogs - but that's large HVAC units used all the time.

About $2.4k for a 24K Daikin with heat. If you can provision electrical and set the lines, you're real close to having someone come out and commission it for not much more. Or if you can work on cars, you can work on one of these..

 

[Centex Hokie]

I haven't installed Mr. Cool, but they all seem to have separate condensate drain lines. They are designed to drain to the outside, but you can install pumps on them if gravity drain is problematic. In your case, as long as the P-trap of the sink is below the unit - you can make it work.

From experience, I don't like HVAC drains going into my plumbing. Myself and other people have had this eventually cause fairly frequent clogs - but that's large HVAC units used all the time.

About $2.4k for a 24K Daikin with heat. If you can provision electrical and set the lines, you're real close to having someone come out and commission it for not much more. Or if you can work on cars, you can work on one of these..

I decided to go with a Mr Cool Olympus 24K. I am going to do the mechanical and electrical installation and an AC vendor has agreed to vacuum it and do the startup and commissioning for $400. I just received it this week and will probably install it next week. So all in for about $2250.

 

[dcg9381]

That's awesome... I just looked that up, that's a 20 SEER unit!

 

[strutaeng]

That's the one I got too! Installing in a couple of weeks...

 

[texastaco11]

I maybe doing a Mr Cool DIY. Quote for a Gree installed was $3,985.91 and for a Mitsubishi $4,824.00. The electrical is already done and I have a sink right under where the head unit is going for a drain. Can the drain on a Mr Cool DIY be separated to stay inside?

Thanks.

I just installed the diy 24k unit and ran the line set up into my attic and then the drain line down and out of the exterior wall it was mounted on.

Sorry I should have clarified, I cut the suggested hole directly behind the unit and ran the drain line down in the stud cavity then out the lower part of the exterior wall and out of the garage. Meanwhile the compressor lines go out and up then to the rear of the 3rd bay of the garage. The wife didn't like the idea of me running the main lineset on the side of the house where it could be seen from the street. We compromised with a small drain line coming out of the lower 3rd of the wall.


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[Centex Hokie]

Looks Good.

 

[dcg9381]

Lines are going the wrong way.
I assume you installed a pump?

 

[texastaco11]

Lines are going the wrong way.
I assume you installed a pump?

Sorry I should have clarified, I cut the suggested hole directly behind the unit and ran the drain line down in the stud cavity then out the lower part of the exterior wall and out of the garage. Meanwhile the compressor lines go out and up then to the rear of the 3rd bay of the garage. The wife didn't like the idea of me running the main lineset on the side of the house where it could be seen from the street. We compromised with a small drain line coming out of the lower 3rd of the wall.

 

[Fixin'Stuff]

I decided to go with a Mr Cool Olympus 24K. I am going to do the mechanical and electrical installation and an AC vendor has agreed to vacuum it and do the startup and commissioning for $400. I just received it this week and will probably install it next week. So all in for about $2250.

You might want to shop around a bit. I went with the Mr. Cool Oasis ES and found a neighbor that does commercial refrigeration to do the vacuum and startup. Paid $100 (and got a receipt for the work, for warranty purposes) and it took about 1 hour. $400 for 1 hour seems quite steep to me.

You'll have already done the hard part. The rest is quick and easy.

 

[dcg9381]

Agree.. I had one leak, someone came out to find it, re-evac, add refrigerant, $200.
$400 for a vacuum test and turning on is pretty high dollar. You can fly me in for that much..