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Thread: O/T Heating the shop, gas vs. electric?

  1. #1
    chainfeed is online now Cast Iron
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    Default O/T Heating the shop, gas vs. electric?

    So, I'm about ready to add heat to my small shop at home, its about 18x24, 2x4 walls and 2x6 rafters both with fiberglass insulation. The house has natural gas but there is no line out to the shop which is only about 20 feet from where the gas line enters the house. Anywho, should I fork out the cash to have a line run then buy a gas heater or just get a electric heat (cheaper than the gas units by quite a bit) and hook that up? I'm putting a 100 amp subpanel in the shop so I'll have plenty of juice.

    Thoughts?

  2. #2
    Big B is online now Stainless
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    Expect electric to cost a lot more than gas to heat. Probably worth the time and effort to put the gas line in.

    Big B
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    swarf_rat is online now Titanium
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    This is a pretty simple engineering economics calculation. In my area, 1 therm of gas is about $1, while 1 KWH of electricity is $0.15 at night and $0.28 in the daytime. 1 therm of gas is equivalent to approximately 29 KWH of electricity, but the gas furnace will only be 80% efficiency , so call it 23 KWH. So during the day, electricity about 6.4 times more expensive, at night only 3.4 times more expensive.

    As an aside, it would seem to be marginally profitable to buy gas from the power company, generate electricity with it, and sell it back to them - at least during the day. The day/night differential for electricity makes it not quite profitable to buy electricity during the night, store the energy, and sell it back during the day.

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    BobRenz is offline Stainless
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    Use gas. I had a gas unit heater added to my garage when I built my home, and I've never regretted using gas instead of electric heat.
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  5. #5
    chainfeed is online now Cast Iron
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    Quote Originally Posted by swarf_rat View Post
    This is a pretty simple engineering economics calculation. In my area, 1 therm of gas is about $1, while 1 KWH of electricity is $0.15 at night and $0.28 in the daytime. 1 therm of gas is equivalent to approximately 29 KWH of electricity, but the gas furnace will only be 80% efficiency , so call it 23 KWH. So during the day, electricity about 6.4 times more expensive, at night only 3.4 times more expensive.

    As an aside, it would seem to be marginally profitable to buy gas from the power company, generate electricity with it, and sell it back to them - at least during the day. The day/night differential for electricity makes it not quite profitable to buy electricity during the night, store the energy, and sell it back during the day.
    So the equivalent to the gas will cost about $3.45 for electric at night at least? Now i just need to figure approx. therms to heat the place and figure a payback timeline.

  6. #6
    Anvil Jenkins is offline Hot Rolled
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    As the other poster showed it will depend on the cost of electricity per kwh, I think it runs $.10 with no day/night differential. I used electric, mine is a detached building, and my heated area is smaller.

    You just have to do the math on heating costs and back figure the cost to install the system and figure the payback rate. Natural gas prices have dropped a lot since I put in my electric unit heater. It is about HALF now what it was when I did that :-). 2006 it was $15.29 it is now $7.58.

    Bill

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    Big B is online now Stainless
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    Quote Originally Posted by swarf_rat View Post
    As an aside, it would seem to be marginally profitable to buy gas from the power company, generate electricity with it, and sell it back to them - at least during the day. The day/night differential for electricity makes it not quite profitable to buy electricity during the night, store the energy, and sell it back during the day.
    Swarf,

    I like your idea but the power company will not buy back power at retail. They pay wholesale if they will buy it back at all. The best you can probably do is to offset your usage, therefore getting retail for it. But even that is easier said than done. Things like automatic transfer switches for the safety of the linemen make it cost prohibitive unless you are getting your power for free from the sun, wind or some other renewable source.

    Big B

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    jmullett is offline Plastic
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    Depends if you are going to keep it heated all the time or not. If you only use it occasionally, you might find a good case for IR electric heater(s) pointed where you are working more economical and quicker than trying bring the air temperature up in the whole of the shop with a furnace. Plus, if you do let the air temperature fluctuate above and below the due point you will have condensation/rust issues on your tools. IR heaters don't rally heat the air but rather the objects that absorb the radiation from them.

    I personally had the opportunity to install floor heat in my 80 ft. x 100 ft. when I built it 7 years ago in northwest Ohio and heat the whole thing at 68-70 F with 1200-1500 gallons of propane using a 175,000 BTU tank-less water heater. It was the best decision I ever made.

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    chainfeed is online now Cast Iron
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    i could do radiant as I am about to pour a new floor

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    SteveF is offline Stainless
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    If you want correct comparison numbers you need to plug your local energy costs and system efficiencies into this spreadsheet.

    www.eia.gov/neic/experts/heatcalc.xls

    If you want a rough idea of the building’s energy usage, this spreadsheet will help. Note that this does calculations for Colorado so the T values in column G need to be adjusted for your local climate. In this part of Colorado the design Winter temp is 0 and the desired inside temp is 68, so the heater needs to add 68 minus 0 equals 68 degrees of heat. The ground temp is rated at 43 so 68 minus 43 equals 25 degrees of heat through the surfaces in contact with the ground.

    www.pprbd.org/plancheck/Heatcalcpublic-v2.xls

    So open this PDF and find your city. Let’s say it’s Boston with a design Winter temp of 12.
    The T values in Column G should be 68 minus 12 equals 56 (replace all the values of 68 with 56) and, if you bump up the ground temp to 45 then 68 minus 45 equals 23 (replace all values of 25 with 23). In the likely event you don’t feel a need to keep the shop at a constant 68 degrees you can lower that number as well which further reduces the energy needed.

    http://www.energystar.gov/ia/partner...itions_508.pdf

    Happy calculating!

    Steve

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    jmullett is offline Plastic
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    If you plan to use it full time, well worth it, and you can tackle it yourself making the cost a wash compared to a furnace. I recommend the 2" pink board rigid polystyrene on top of your vapor barrier and around the slab as well. Six inch wire mesh fencing makes a nice thing to zip tie your 1/2" radiant pex tubing to. You can always add rebar on top of the mesh and gives a nice stop to pull the mesh up to during the pour. Whatever heat you decide on don't skimp on the vapor barrier otherwise moisture will wick up and rust your stuff.

    Nothing is as nice as laying on a warm slab while wrenching underneath your truck. Floor heat does not have a fast warm up/response time, but has an excellent recovery time, like when an overhead door is opened. It is not something you can put on a timer and turn down at night and up in the morning. You pick your temperature and stick with it. It will also stay warm for days inside if the power goes out or propane tank runs dry.

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    rdhem2 is offline Aluminum
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    Great bunch of answers. I agree with all. Only down side with radiant heat is if not installed correctly it will fry your head while your feet freeze. Once it heats the area it is fine. As they said it is not something you switch off and on.

    The in-floor systems are wonderful. Just keep track of where it is should you ever anchor anything to the floor. It is a little tough to patch up.

    Forgot, 1st choice NGas, #2 Propane, #3 electric. Initial cost is nothing compared to years of day by day operation.

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    if you decide on gas, I have only scholastic numbers to work on. natural gas has 1000 btus per cu ft. Propane has 2500 btu's pre cu ft. if the price is right, drop a propane tank in there. cheers stay warm this winter. . . I know I wont be.

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    swarf_rat is online now Titanium
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    Quote Originally Posted by Big B View Post
    Swarf,

    I like your idea but the power company will not buy back power at retail. They pay wholesale if they will buy it back at all. The best you can probably do is to offset your usage, therefore getting retail for it. But even that is easier said than done. Things like automatic transfer switches for the safety of the linemen make it cost prohibitive unless you are getting your power for free from the sun, wind or some other renewable source.

    Big B
    A little off the Off Topic, but here in California, the power company - by law - has to buy what I generate, at market prices. The meter runs backwards at whatever the time-of-day price is. At the end of the year if I am positive they send me a check. But right now I have only a 4.5 KW solar array, and I end up paying every year. Solar cells have dropped so much in price I am thinking of doubling the size of the array.

    The power company made me put in a large manual transfer switch at great cost, which they never use. Grid tied inverters that are UL approved automatically shut down when the line goes down.

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    barky is offline Aluminum
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    Around here they have to buy it back at retail up to 20 KW. After that it drops to something like .03 per KW. A friend of mine has several small hydro units around the county and does quite well $$

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    Sea Farmer is offline Titanium
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    Pricing varies across Mass of course, but on the Cape gas is so much cheaper that you can do the math in your head just by looking at the bills. And when the wind farm comes online electricity will be even more expensive, to account for some of the subsidies.

    That being said, I do use an electric heater for a few minutes each am while my wood stove gets going. But never more than 15 minutes or so--and I can see the difference in the bills when I do.

    But if you're talking about 24-hour heat, to keep things from rusting, I'd go with gas.
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    SteveF is offline Stainless
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    Quote Originally Posted by alonzo83 View Post
    if you decide on gas, I have only scholastic numbers to work on. natural gas has 1000 btus per cu ft. Propane has 2500 btu's pre cu ft. if the price is right, drop a propane tank in there. cheers stay warm this winter. . . I know I wont be.
    The amount of heat (BTUs) per unit is irrelevant. What matters is how much does a BTU cost.

    If you look at the spreadsheet I linked, the cost per BTU with propane is about three times as much as the cost with natural gas.

    Regarding a couple of comments about radiant floor heating systems. Yes, they are nice. Yes, they keep a nice stable temp. However, you still have to heat the slab enough to generate the heat needed to keep the building temp up. If his building loses 20K BTUs of heat per hour at a certain outside temp, you still have to generate 20K of BTUs and it doesn't matter if you are heating the floor or heating the air.

    BTW, I have a radiant floor heating system in my 28' x 40' shop which hasn't been hooked up. Due to the 5" in the walls and 7" on the roof deck of closed cell spray foam and the 2" of XPS foam under the slab, the building doesn't go below mid-50s on the coldest days (note, this is NC, not MN) with two 1500 watt baseboard heaters that cost me about $80 per winter to run. If someone is concerned about the potential heating cost, insulate the heck out of the building (preferable with something other than fiberglass) first.

    Steve

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    scadvice's Avatar
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    Here you go...US STOVE CO Window Pellet Stove By Us Stove Co - Tools - Hand Tools - Chisels ...Let us know how it works! Just kidding.

    If your pouring a new floor I'd go with a heated floor natural gas one too...

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    Ajc123 is offline Aluminum
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    Just to throw something else in the mix Home - Kroll Heaters Australia they use waste oil,not sure on costs though,but here they market it as cheaper than natural gas

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    barky is offline Aluminum
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    If you can get enough woodland critters to burrow under your slab you wont have to heat it at all.

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