Time to figure out heating and cooling

[chuey_316]

While I wait on the last of my bits to come in for electrical, and for the next week straight of rain to be done so I can finish my trench, it's time to fighur out how many btu's I am going to need to keep my space comfortable.

I have been doing allot of reading here and elsewhere, and the numbers suggested are kinda all over the place. Ranging from 25 btu per sq ft, to 50+, and I could definitely use some advice with this.

My garage is 550 sq feet. The walls are 8ft, and the ceiling will run up the rafters, and under the collar ties, which are at 10ft. I've attached a picture in case my explanation isn't clear.

The roof will be sprayed with closed cell. The walls will either have 2" of closed cell, or be dense packed with cellulose. Have not decided on that yet. There are also 2 9x7 R6.3 insulated doors, no windows, and there will be 1 side entry door.

I will be going with either a mini split or an ac/heat combo through wall unit. Allot of people out there saying that an 18-24k would be bare minimum for this size, while others say that 12k is more than enough.

I am In SW MI as well, so our winters can range from 20F lows, down to -20 depending on the year, and our highs in the summer are normally in the 80's to 90's, but can reach 100+.

 

[dscheidt]

What are the calculated loads? If you can't answer that, then that's your first step. This is a science, not black magic. There is no good reason to guess[1], and lots of good reasons to do it right. Calculate the load, then you can figure out what the right size equipment is.

[1] HVAC contractors guess because they're lazy, stupid, or scammers. Selling oversized equipment makes them more money, both upfront, and down the road when it breaks down prematurely.

 

[pembol]

As others have said - do the actual calculations, this is about as easy as it gets for load calcs.

But for a gut feeling an 18k mini split would likely be plenty. If the cost differential isn't too bad, you could go with a 24k, which would have the advantage that it could heat up/cool down the space faster if you only plan on conditioning it while you use it. One of the many advantages of mini splits is that they have great turn down ratios and can piddle along at 5k output once the space is up to temperature.

 

[chuey_316]

Tried a few different load calculators. They were all fairly consistent that 12k btu would be sufficient for cooling, but they were all over with the heat, ranging from 12k to 24k.

I'd meet in the middle and go for an 18k, but I don't want to go too small. At the same time I don't want to spend allot more for too much either. I just want to be able to be able to keep the temp around 55-60 in the winter, and 65-68 or so in the summer.

I'll probably just keep an eye open for a good deal on a 24k, even if I have to wait another year and use the torpedo for another winter.

 

[dwall174]

Tried a few different load calculators. They were all fairly consistent that 12k btu would be sufficient for cooling, but they were all over with the heat

I have a little smaller garage 440sq. ft. also in Michigan, SE side.
Tried several on-line load calculators & I also got mixed results. 12k sounds fine for cooling, but I'm thinking 18k may be better for heating?
I've also noticed that a 20 or higher SEER2 rating is better for us in the colder claimants.

Doug

 

[Skellyii]

I have just short of 1K sqft with 11.5' ceilings and average insulation. We're a little south of you so our winters are slightly warmer and summers slightly hotter.

I ran the calculators for my garage and got 24K. I also asked an HVAC buddy of mine and he also said get a 24K. It's been in for two hot seasons and a cold winter, and the 24K seems to be more than enough.

I would think that with your size, and better insulation, that the 18K would do just fine.

 

[dwall174]

I'll probably just keep an eye open for a good deal on a 24k

I just ordered a DELLA Serena Series 18000 BTU SEER2 22 Mini-Split Heat Pump AC. I ordered it through their web site, https://dellahome.com/ they currently have an independents day sale. I read a bunch of good reviews on them! Their also available through Amazon, so maybe watch for any Prime Days sales.

 

[dwall174]

The 18K DELLA unit I decided on is probably a little over sized for my garage, but I still need to finish installing a ceiling in my old garage. It's a lot more fun trying to install a ceiling in a already overcrowded garage.
Until I get the ceiling & insulation finished, the add BTU's should help offset the lack of proper insulation.


The 18k unit I decided on is rated down to 5 degrees for heating which should be good for most of the winter. When it does occasionally drop below "0" I generally don't work out in the garage much anyway.
I also have a 6,000-Watt Heat Storm heater

that may help out on those below "0" days. However, running both at the same time would put my current power supply close to its limit & I wouldn't be able to run anything like my air compressor or table saw/dust-collector.


Doug

 

[chinboys]

Too small of a unit means it runs longer thus consumes more electricity (power).
Too large of a unit means it will short cycle more often or the inverter based compressor will run accordingly to the load and you might feel clamy.
Get a Manual J calculation done. You can get this calculation on the WWW.

Then you need to insulate as well as vapor barrier both the inside and outside of the garage.
The amount of insulation should be at a minimum to the standards in your area.
Close cell spray foam is fantastic for an exterior insulation and vapor barrier.
It isn't good if you decide to plywood or sheetrock the interior as indoor generated humidity will permeate these organic based things and may result in black mold growing between the interior close cell foam and the wall.

Heat always moves (transfers) towards the cold. Heat transfers via conduction and convection.
Moisture in the air relative to temperature will always drive via osmosis towards space with lower relative humidity.
Stop all drafts from coming in as well as going out will reduce the run times of the system.
Keep the doors and windows closed.
Using the system intermittenly may not be as economical as running it at a constant temp during the cooling or heating season.

Lastly, keep the interior air circulating. One can reduce their cooling or heating setpoints as result of having a breeze.

 

[pcmeiners]

I've also noticed that a 20 or higher SEER2 rating is better for us in the colder claimants.

Seer numbers are over rated for anywhere you need heat, your heat will cost far more than cooling unless you live in a "broil" state as in Texas, Arizona, New Mexico. Concentrate on a higher HSPF number as Michigan has long cold (heat expensive) winters.

 

[Bert_]

Too small of a unit means it runs longer thus consumes more electricity (power).
Too large of a unit means it will short cycle more often or the inverter based compressor will run accordingly to the load and you might feel clamy.
Get a Manual J calculation done. You can get this calculation on the WWW.

Then you need to insulate as well as vapor barrier both the inside and outside of the garage.
The amount of insulation should be at a minimum to the standards in your area.
Close cell spray foam is fantastic for an exterior insulation and vapor barrier.
It isn't good if you decide to plywood or sheetrock the interior as indoor generated humidity will permeate these organic based things and may result in black mold growing between the interior close cell foam and the wall.

Heat always moves (transfers) towards the cold. Heat transfers via conduction and convection.
Moisture in the air relative to temperature will always drive via osmosis towards space with lower relative humidity.
Stop all drafts from coming in as well as going out will reduce the run times of the system.
Keep the doors and windows closed.
Using the system intermittenly may not be as economical as running it at a constant temp during the cooling or heating season.

Lastly, keep the interior air circulating. One can reduce their cooling or heating setpoints as result of having a breeze.

What uses more power 500 watts for 2 hours or 1000 watts for one hour?

 

[Bert_]

This is a reasonably good calculator

HVAC Load Calculation - Maunualj - Whole House Loadcalc

ManualJ load calculator, HVAC calculation, Whole house, - www.loadcalc.net

loadcalc.net

 

[danski0224]

What uses more power 500 watts for 2 hours or 1000 watts for one hour?

I don't know, but a ton of feathers is lighter than a ton of bricks...

 

[danski0224]

While I wait on the last of my bits to come in for electrical, and for the next week straight of rain to be done so I can finish my trench, it's time to fighur out how many btu's I am going to need to keep my space comfortable.

I have been doing allot of reading here and elsewhere, and the numbers suggested are kinda all over the place. Ranging from 25 btu per sq ft, to 50+, and I could definitely use some advice with this.

My garage is 550 sq feet. The walls are 8ft, and the ceiling will run up the rafters, and under the collar ties, which are at 10ft. I've attached a picture in case my explanation isn't clear.

The roof will be sprayed with closed cell. The walls will either have 2" of closed cell, or be dense packed with cellulose. Have not decided on that yet. There are also 2 9x7 R6.3 insulated doors, no windows, and there will be 1 side entry door.

I will be going with either a mini split or an ac/heat combo through wall unit. Allot of people out there saying that an 18-24k would be bare minimum for this size, while others say that 12k is more than enough.

I am In SW MI as well, so our winters can range from 20F lows, down to -20 depending on the year, and our highs in the summer are normally in the 80's to 90's, but can reach 100+.

You need to either do your own research on doing a load calculation, or pay someone to do it.

The spray foam, if properly applied, will make a huge difference compared to traditional methods. Biggest point of loss will be the overhead door, which skews assumptions.

Just based on your description, you should be well under 12,000 btu for cooling and probably the same or less for heating, with the overhead door being the monkey-wrench in the assumptions.

 

[dwall174]

I just ordered a DELLA Serena Series 18000 BTU SEER2 22 Mini-Split Heat Pump AC.

I read a bunch of good reviews on them!

Apparently, I didn't read enough reviews on their customer service.
After finding out that my city has some stupid regulations on putting in a heating/cooling system in a detached garage, I ended up canceling my order for the mini split. Being it was the Holiday weekend naturally nothing got processed or shipped yet. It took me over 3-hours to finally get ahold of someone to cancel my order, and then I'm not 100% sure it wasn't pushed through just to try to make a sale. About 4-hours after I was told my order was canceled, I got an e-mail from Shop Pay stating that my Buy-Now-Pay-Later loan was approved.
Needless to say, knowing what I just went through with their so-called customer service I wouldn't recommend DELLA at-least through their website.

 

[u3b3rg33k]

Tried a few different load calculators. They were all fairly consistent that 12k btu would be sufficient for cooling, but they were all over with the heat, ranging from 12k to 24k.

I'd meet in the middle and go for an 18k, but I don't want to go too small. At the same time I don't want to spend allot more for too much either. I just want to be able to be able to keep the temp around 55-60 in the winter, and 65-68 or so in the summer.

I'll probably just keep an eye open for a good deal on a 24k, even if I have to wait another year and use the torpedo for another winter.

i grabbed a 24k and so far so good. similar latitude, and I have a dehumidifier in the garage as well.
the nice thing about minisplits is oversizing doesn't really hurt you, so you have that extra oomph for when you park a hot car in there and it's 95F outside, or you open the door in february to get the snowblower out.

insulated 2x6 top and 2x4 walls and just shy of 500sqft, i'm burning 12kWh/day when it's in the 90s between the dehumidifier and the minisplit to keep it 75F 50% rh inside.

 

[pcmeiners]

I don't know, but a ton of feathers is lighter than a ton of bricks...

Is that AIs final answer.

 

[pbon]

Insulated 550SF with low ceilings —- an 18k widow/wall AC with built in 12k heater should do it. Worked for me with 750SF in the Northeast. I did later change the heat to a natural gas hanging shop heater but mostly because I wanted to and for the faster recovery after opening one of the garage doors. Today I might look at 18k to 24k mini splits

 

[Ak Jim]

Apparently, I didn't read enough reviews on their customer service.
After finding out that my city has some stupid regulations on putting in a heating/cooling system in a detached garage, I ended up canceling my order for the mini split. Being it was the Holiday weekend naturally nothing got processed or shipped yet. It took me over 3-hours to finally get ahold of someone to cancel my order, and then I'm not 100% sure it wasn't pushed through just to try to make a sale. About 4-hours after I was told my order was canceled, I got an e-mail from Shop Pay stating that my Buy-Now-Pay-Later loan was approved.
Needless to say, knowing what I just went through with their so-called customer service I wouldn't recommend DELLA at-least through their website.

So you can’t beat or cool your garage? What is the reasoning for that rule?