Cooling Shop

[Deltarat]

I have read the threads on the BTUs needed per square feet, but are the figured with a 8' ceiling? I will have a 30x35 with a 12' ceiling. Will that increase my BTU capacity by 50% due to increase in volume? Or would it help by allowing the hotter air to rise above head level?

 

[Steve in Mi]

The wall surface area heat loss is increased by ~50% but it's not 50% of the total heat loss as the ceiling and floor losses are unchanged.

 

[Steve in Mi]

Actually there are a couple of links in this thread that may shed some light on your requirements. At least I hope the calculators make allowance for wall height - not having looked at the links first hand.

http://www.garagejournal.com/forum/showthread.php?t=10769

I did some checking and found the first link is not working and the second link does have wall height in the calculation.

Direct link; http://www.heatershop.com/btu_calculator.htm

 

[Deltarat]

I guess cooling would be the same as heating. According to that the 50% increase in volume only changed the BTUs by 25%.

 

[Steve in Mi]

The btu calculation is based on square feet of surface area not on volume. It is thru the surface area (walls, ceiling and floor) that heat is lost (heating)or gained (cooling).

 

[Deltarat]

Thanks,Steve. That is good information to know. I know nothing about heat and air.52,200 BTUs, I guess I could use 2- 24,000-28,000 window units, with one on each side of the shop would do what I want to do. I could probably run one most of the time.

 

[Steve in Mi]

Not knowing more about your location and construction I can only add that insulation will make a very big difference in the comfort and cost of heating or cooling your space. This should be clear by pluging in all the same numbers for the different levels of insulation. Also, insulation payback times are short - one of the things that pays dividends in savings year after year. If I read between the lines correctly you are still in the pre-build stage so I suggest you consider carefully how you will spend your insulation dollars.

 

[Deltarat]

Yes, I am in the pre-build stage. I am in N. Ms. and I am in the pre-building stage. I will be stick built. I am considering 2x4 or 2x6 studs. I don't know if the increase cost of studs and increased insulation is worth it in our climate. If it is worth it, I don't mind the extra cost. I am considering blown in insulation in the walls and ceiling. Any thoughts?

 

[JohnZ]

Insulation makes ALL the difference, and can only be done right during the pre-build planning stage. I'm in Michigan, where we get pretty cold in the winter, and I designed our new home/garage seven years ago to take advantage of all the insulation I could get for heating/cooling savings.

We designed for 2x6 studs to get maximum space for wall insulation (R-26), and I have R-58 in the 12' ceiling. Also insulated under the 44' x 58' garage slab with 10-mil poly, covered with 5/8"-thick 4'x8' sheets of high-density closed-cell foam with heavy foil on both sides (for both insulation and as an absolute barrier against moisture migration under the epoxy coating). The 18' x 8' insulated sectional doors are 1-1/4"-thick steel/foam/steel sandwich with tubular seals between the panels, and tightly-fitted double vinyl seals around the perimeter. The name of the game is "super-insulation".

As a result, it's nice and warm and dry (including the floor) all winter long with only a few hours of daily usage of the 125,000-BTU Reznor ceiling-mounted forced-air gas unit heater, and a 42,000-BTU mini-split A/C unit cools the space at 75* with no problem at all, even in continuous 90*+ weather in the summer. The Reznor is WAY more heating capacity than I need, but the contractor had never seen a garage insulated the way mine is; could have gone with a much smaller one if we knew then how much difference the insulation package would really make.

After the building is finished is NOT the time you want to find out that you should have spent a little more on insulation; you can only do it once - do it right and you'll be glad you did in the long run.

 

[Steve in Mi]

Yes, I am in the pre-build stage. ..... I don't know if the increase cost of studs and increased insulation is worth it in our climate. If it is worth it, I don't mind the extra cost. I am considering blown in insulation in the walls and ceiling. Any thoughts?

You can run the figures for your garage space, convert to KWH for ''no insulation'' and then for ''good insulation'' (or whatever level of comfort you desire). Calculate the difference apply your local KWH rate to put it terms of dollars and multiply by say 5 years (5 yr. payback period, you'll be even in five years) and you have a measure of the $$$'s you can spend now for insulation. After the fifth year you will pocket that savings each and every year. AND, it gets better still, energy cost are increasing all the while so the savings is increasing too. This exercise is only one idea of how you can work the numbers but it should get the juices flowing. How much time you will spend in your garage also has to be factored into your plan. Initially I was going to put 'in floor' radiant heat in my shop but decided not to because I didn't see myself using it full time and the longer heat up time of that system didn't appeal to me. My shop has turned out to be very reasonable to heat so I don't give it a lot of thought if I miss a few days or a week now and then when it is idle.

Look at the actual difference in the cost of 2X6 vs. 2X4's for the whole job - my guess is that if you decide you need extra space for insulation it is only a minor upgrade as a percentage of the total build cost. I went with the 2X6's to tuck in more insulation but also for strength to my second floor rated @ > 125 pounds per sq. ft., to give me more space for electrical and air in the walls and frankly the 2X6 lumber at the time (1981) was better quality material than the 2X4's. Much straighter and fewer knots. I hand picked every piece of construction material that went into my DREAM SHOP, 8 foot studs were cut from 16 footers (better quality still in longer lengths). 6" of fiberglass and 1" of Dow rigid foam wrap my entire space from the bottom plate upward. In addition to 1" of Dow rigid foam under the floor, I have 1" inside and 1" outside my 42" foundation block walls. Windows are casement triple pane and all doors are foam core insulated. 6 mil poly moisture barrier behind all interior sheeting (on the warm side) and under the foam the wire reinforced concrete floor rest on. Below the poly moisture barrier (under the floor) is also a double layer of Dow Saran vapor barrier film - don't ask, I had it so I used it.

So what did I get for my effort to insulate and wrap my shop. Besides a big smile on my face every time I think about how my planning paid off .... lets see it's a 28' X 48' two story structure (see a teeny tiny picture of it to the left) heated to 63-65 degrees, a comfortable working temperature for me (except on rear occasions when I'm trying to force some painted project or glue-up to dry faster in which case I'll bump it up some). Since 1999 I've heated 24/7 in our ~6 month heating season with a dual burner 70k btu natural gas counterflow forced air furnace. My best estimate is that last years heating season cost was $140.00 up from 90 something dollars in 1999.

[[ no A/C because it doesn't get above 73 degrees inside in the Summers (the high was 71-72 so far this Summer for a couple of days) ]]

The big smile - priceless!

Almost forgot,

I am considering blown in insulation in the walls and ceiling. Any thoughts?

I would be concerned about adequate fill (bridging over electrical, plumbing etc. in the walls and voids under electrical boxes etc plus the settling effect of blown in insulation in the walls. For these reasons I wouldn't use it in the wall cavity.

 

[Deltarat]

Steve, that sounds like a first class job. You could probably heat that thing in Ms. with a 100w light bulb. I am leaning towards the 2x6 studs to get more insulation.I think the 2x6 studs add about $250 to the build.But the added insulation should recoup that pretty quick. I will use roll in the walls and maybe blown in the ceiling.
I will have AC since we have long hot summers here over 100.
Thanks for your help and any other suggestions would be welcome.
Bill