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Electric garage heaters ?

Post in 'DIY and General non-hearth advice' started by Pallet Pete, Aug 11, 2013.

  1. Pallet Pete

    Pallet Pete Guest

    I am starting to consider a ceiling mount garage heater and need some help with the math.

    The garage is

    22.8 long
    23.8 wide
    15ft tall front
    10ft tall rear

    Here is my first issue how do I determine the cubic ft with a slanted roof ?

    Second my electric company charges 13cpm per kwh so how would I determine the per hour charge on a 5000 watt heater.

    Here is what I am considering.
    http://www.lowes.com/pd_359041-49285-FUH54_0__?productId=3499392

    Currently I use a 80,000 btu heater that burns a 20 gallon propane tank in 4-8 hours depending on how cold it is outside. Being in Michigan winters its 4 hours when below zero out. I was considering wood or pellet but I don't want to give up the floor space and the county gives you almighty heck about it too.

    Thanks
    Pete

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  2. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    5,000 watt heater cooks off 5 kwh per hour.

    Sixty-five cents an hour.
    Pallet Pete likes this.
  3. heat seeker

    heat seeker Minister of Fire

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    Figure the volume of the roof area seperately. Draw an imaginary line across one end of the gable where the ceiling would be, if you had one. Measure, in the center, the height from the "ceiling" to the peak .Then measure the width of the gable at the bottom. Multiply the two dimensions, then divide by two. That gives the area of the gable. Multiply that number times the length of the garage. You now have the volume of your "attic".

    The formula for the area of the gable: ½bh, which is ½ times the base times the height of the triangle.

    http://www.ask.com/web?q=area of a triangle formula&qsrc=178&o=0&l=dir

    The volume of the work area is Length times Width times Height. Add the two volumes together, and you have the total volume. You'd save a load of heat if you could install some sort of ceiling to isolate the attic area.
    Pallet Pete likes this.
  4. Pallet Pete

    Pallet Pete Guest

    At $12 for 20 pounds of propane electric is cheaper alright ! Propane is $144 a day vs $15.6 a day for electric 5000 watt. Thanks BB that is a seller.

    Now for the cubic ft.

    I did it at 12 ft height because the front was 14 and the back 10. My logic is that if I where to flatten it the back would rise two feet and the front lower two. Does that even make sense lol. I came up with 6511 cubic ft.
    Pete
  5. heat seeker

    heat seeker Minister of Fire

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    Makes sense, I didn't allow for the different heights. Assuming that the roofline is straight, you got it right.
    Pallet Pete likes this.
  6. Pallet Pete

    Pallet Pete Guest

    Thanks it is straight. You guys are great !

    Pete
  7. Pallet Pete

    Pallet Pete Guest

    Does anyone have experience with this style of heaters and how well they work ?

    Pete
  8. Grisu

    Grisu Minister of Fire

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    Be careful not to underestimate your heating load with the electric heater. 1 gallon of propane = 91,000 BTU * 20 = ~1.8 mill BTU. If the heater is 75% efficient you have a heating load of 1.35 mill BTU in 4 to 8 hrs. 1 kWh has 3,400 BTU, the max per hour you will get are therefore 3,400 * 5 = 17,000 BTU or in 4 hrs 68,000 BTU. Unless your propane heater is awfully inefficient (or I made a stupid mistake with my numbers) the system you are thinking of will not be able to get the garage space heated.

    To calculate what is really cheaper for heating:
    1 pound propane = $0.60 = 22,000 BTU; cost per 1000 BTU: 2.72 cent
    1 kWh electricity = $0.13 = 3,400 BTU; cost per 1000 BTU: 3.82 cent

    Only when the propane heater is less than 70% efficient you will save money but it will take a while to recoup the cost for such a rather large electric heater that gives you at least 250,000 BTU per hour (75,000 watt system) when it is really cold outside. Have you thought about insulating instead? Maybe just a dropped ceiling with some insulation above would help.

    P.S. You could also test if a 5000 watt heater would be sufficient assuming your circuit can handle it. Borrow from friends/family 3 space heaters in the winter. Those usually use 1500 watt on high. Let them all run continuously for a while in your garage and see if they get it up to temp. If it is not even close your 5000 watt heater will be too small.
    woodgeek and jharkin like this.
  9. Joful

    Joful Minister of Fire

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    (22.8 x 23.8 x 10) + 1/2 x (22.8 x 23.8 x 5) = 5426 + 1357 = 6783 cu.ft.

    I had an electric heater in my last shop, heating only 2261 cu.ft. of extremely well-insulated space (minus one overhead door). I don't remember the numbers now, but it was painfully expensive to keep it going all winter, particularly when I was shooting paint, and had to keep temps close to 70F. I'd usually keep it closer to 55F, though.
  10. Pallet Pete

    Pallet Pete Guest

    Yes I did think about insulating the ceiling but I use the rafters for storage so that's not really feasible to do right now. Thanks for all the good info I will certainly research more.

    Pete
  11. Pallet Pete

    Pallet Pete Guest

    Joful I am not using heat all the time but instead on the weekends and possibly weeknights for a couple hours at a time. That's why propane is so painful for me lol 4 hours 20lbs ! I think I would be willing to pay the same price but with the convenience of not filling a tank every time I use the garage. ( not that I want too )

    Pete
  12. stee6043

    stee6043 Minister of Fire

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    Do you have natural gas? I think you're going to find that properly heating your garage with electric is going to come with a fair bit of upfront cost.

    The heater you linked above is 240V. Do you have 240V wired to your garage already? If not, how far will you have to run a new line? I assume you're going to need a 30amp 240v circuit for this rig. Copper is expensive these days. Ground fault 240v breakers are even more redicilous (if required).

    You can't beat electric in terms of efficiency. But for the amount of use you're talking about I think you're going to be hard pressed to beat gas/propane in bang-for-the-buck. Maybe you could get a bigger propane bottle if you don't have natural gas available? My two cents only.
  13. Pallet Pete

    Pallet Pete Guest

    I rewired my garage over the summer with 60amp service in the garage so that shouldn't be an issue. And yes its pricey but worth it because I weld frequently. Propane is expensive a bigger tank would still be just as much as 20 pound tanks but a fill at once. Our natural gas would cost a fortune to run to the garage otherwise I would do that. They quoted us at $3200 to run it out to the garage. O well sounds like I might have to give up the idea !

    Pete
  14. Highbeam

    Highbeam Minister of Fire

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    That 5000 watt heater uses 5kwh per hour so at 13 cents each the electric will be 65 cents per hour and if you run it all day it will cost you 15.6 bucks. You are only getting like 15700 btus from that per hour though.

    Propane in that burner is only 80% efficient so you are getting 64000 btus per hour or 4 times as much output.

    So the electric cost to get the equivalent heat would be 62.4$ per day.

    Your propane cost is okay at 2.4 per gallon. Something is fishy. Burning 20#s of propane in 4 hours with an 80,000 btu burner is a bit odd. 20# gets you 440000 btus. In four hours you would have to be eating it at a rate of 110000 btus per hour. That's not 80,000.

    You know what might be happening. It's not funny really, but maybe a little. Perhaps you are freezing the little BBQ size tank of propane so the output stops. This happens when you overdraw a small propane tank. Then you think it is empty but really it isn't and you go and exchange the tank for a new one.

    You shouldn't be feeding an 80,000 btu burner with a BBQ tank, it is too small.
    Joful, fbelec and Pallet Pete like this.
  15. semipro

    semipro Minister of Fire

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    Pete, it may be worth running the numbers on using a ductless mini-split heat pump.
    While the up front cost will be much higher, the break-even point may not be as long as you think.
    While it won't necessarily heat the garage quickly you may be able to warm up the place beforehand using a remote control or scheduled operation.
    Pallet Pete likes this.
  16. ScotO

    ScotO Guest

    Hey, what the heck?!?:eek: Put a little woodstove out there, Pete!! just scrounge a little extra wood (or get some pine off of our buddy Dennis up there near you). That pine gets the room warm in no time, just go out a half hour before you plan on being out there and build you a fire.....VOILLA!!

    This IS a woodburning forum, remember? ;lol:p
    Joful likes this.
  17. Highbeam

    Highbeam Minister of Fire

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    Trouble is that the code and most insurance companies forbid a stove in a garage or an outbuilding. Stupid rule and often ignored but in our modern society you have to be careful.
  18. ScotO

    ScotO Guest

    yeah, I know....same goes with my insurance co. in regards to a stove in the garage......they won't allow it.

    But I DO have one in my workshop/barn out in the backyard, and I love that stove. It's nice to be able to go out there and work in good dry heat.....
  19. Highbeam

    Highbeam Minister of Fire

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    I am jealous. My 30x60 shop may not have a solid fuel burner as it is an "outbuilding" according to state farm. I woudl love to use some wood out there.
  20. ScotO

    ScotO Guest

    I don't think I'd even want a shop if I wasn't allowed a woodstove in it......
  21. Pallet Pete

    Pallet Pete Guest

    I wish ! I went through the gates of hell and back already trying to get them to allow an add on furnace in the garage 24" off the floor. It ended up that no insurance company anywhere that I called would allow it or the county for that matter. It is a nightmare to get approval for.

    My other thought is a pellet stove with an outside air kit 15" off the ground. The county will approve that as long as the insurance does. The insurance won't approve it without written consent from the county and the county won't approve it without written consent from the insurance company. What a mess !

    Pete
  22. Pallet Pete

    Pallet Pete Guest

    Maybe I should be looking at coal ? Pot belly stoves are cheap !

    Pete
  23. Highbeam

    Highbeam Minister of Fire

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    For us, the prohibition was "solid fuel heater". So no coal either. I could put in a gas fireplace though.

    Really, those hanging reznor type heaters really kick out the heat but without NG they cost some bucks to run.

    Electric heat is very cheap and easy to install. Yes, it will take a 30 amp circuit but with 60 amps available you have plenty. Remember, your welder isn't a huge demand item. 60 amps is fine for most shops. No open flame, no ducting, no emissions, you already have an endless supply of fuel, etc. Electric has some benefits.
  24. fbelec

    fbelec Minister of Fire

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    also remember that 15 and cents dollar a day is the electric heater running full blast and never shutting down. if it has a thermostat on it and is cycling on and off to maintain a temp it will be cheaper to run
  25. jharkin

    jharkin Minister of Fire

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    Interesting. I had thought the woodstove prohibition was only for garages on the thinking that there may be stoves gasoline or other volatile chemicals in a garage that could get ignited. I certainly see a lot of barns and even large shed workshops around here with stovepipes.

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