Heating Garage- Formula for BtuH

[Gene in NC]

Location Raleigh, NC.

With a little help from Grainger catalog the formula for BtuH to heat a closed space is: cubic ft. x 0.133 x (desired temp - ambient in structure) = BtuH.
Actual will vary by amount of outside air entering. Attached garage may benefit a bit from heat loss from residence.

My garage is 22 x 20 plus a 10 x 10 work area x 9 ceiling =
4,860 x 0.133 x (70 - 30) = 25,855 BtuH. Getting reasonable warm up time may need another 10k BtuH. Assume 30 degree day or temp commonly not much below 30 deg. by 24:00 hrs which is longer than I can last.

Grainger had a 35,000 kero Dayton unit for $159 in 2000 cataloog. Home Depot has, if I recall correctly. 15,000-25,000 propane for $159 plus, I assume, propane tank. Kero would get complaints from "the house".

Have had some success with heat from the house. Mud room, laundry, half bath area has two hot air registers With closed door to the house, open door to garage, set strong fan inside the door, set furnace blower to on, and temp level improves considerably. Have tried 10k BtuH kero heater but didn't help much and exposed to odor. May go with electric supplemental.

Example of justification is: Shop hours for strut replacement on e34 is 5 x $60 or higher plus full "shop retail" on the parts. Non BMW shop wants $600 for e34 struts.

To do, we have 2 x e34 struts, 1 e28 for upper control arms, 1 e30 for driveshaft, 2 Chev trucks for brakes, 1 '76 2002 for complete driveline strip to go into '73 2002 restoration , 1 e28 535 with mystery start but not run, etc. Also have '68 2002 that would make a good drivers school car.

But, the most important project is repair/restore '66 Boston Whaler 17 that must be ready for departure 3/31/06 from Wilmington, bound for Key West via the ICW. Why this March? Because I'm running out of Springs.

[Paul in NZ]

whatever dont forget some ventilation if using a combustion heater....how do you allow for insulation values?

[Gene in NC]

Paul,
No comment from Grainger. Insulation effect unknown. Do recall that ceiling in that mudroom, etc 10 x 12 area was initially not insulated. Effect on a cold day that I installed insulation was immediate and very noticeable.

[Paul in NZ]

grainger prolly allow for an "average" insulation value which of course vary's with building materials and construction methods

[DanDombrowski]

I took an HVAC class in college. Not my field of expertise, but I've done some work in it. For the insulation, you have to get a U value (which is just a engineers term for thermal resistance), and that's based upon some engineering tables. You pick the components the wall is made of (concrete block, stucco, brick face, etc), add em up, take the inverse, and you have your U value. Try Google, search for ASHRAE tables.

The energy you have to put into a space to keep it at a temperature is U * A * Delta T, where A is the area of the wall and Delta T is the temperature difference. The Delta T is usually corrected for air conditioning depending on exposure to the sun and season, but grey wintery conditions wont call for much correction. If you want a real calculation, you have to do a UAdT calculation for the roof and the floor also.

Common units for energy input into the space is Btu per hour, or Btuh, like you've been using. In the end you'll want to pick something a little higher for startup time and leakage, but for a garage without windows you won't need much. Hope this helps, or at least gets you pointed in the right direction to making a more educated HVAC decision.

When I took the class, we discussed mostly commercial applications where a boiler fed with fuel oil was the most efficient, and if it wasn't fuel oil, it was LP gas. With the recent extreme hikes in prices of LP gas, I have no idea what would be most cost efficient for you, but my guess would be "not electric". Yet.

[Gene in NC]

Try this link for comparisons on various methods and fuels. Includes time and cost to "bring up to temp".

http://www.autoexpress.co.uk/product_test/51878/garage_heaters.html

[rob101]

Shouldn't there be some allowance for the thickness of the wall in calculating the energy lost through conduction through the walls. Unless you take that into consideration with your "U" value.

Those calculations should be okay, they should be conservative as they don't take into consideration convection on either sides of the wall either, which increase the thermal resistance.....
as for calculations, i can't work things out in British Thermal units or fahrenheit. SI units and all that i am fine with.

[ChefJRD]

You said the non-BMW shop want $600 for the struts, and I don't know if you included labor in that, but I replaced the front struts a little bit ago and found a helluva deal from Pro Am.

I got the Bilstein touring strust (PNE 3118), which were around $100-110 at both BMA and Bav Auto. But I did a simple google search and found them for $55 at Pro Am!! They're listed at $65 now, but still a good deal. Check the prices out here:

http://www.proamauto.com/page15bbiltcb19.htm