Replies

1. 
   Tim_Rice | Jan 10, 2002 05:03pm | #1

   *
   I would get a propane-fired or dual fuel suspended unit heater (about $570) and a 30 gallon portable tank to run it. Set it in a corner out of the way where you could vent it out the wall and have some place to store the tank.

   An electric version (7.5 kW, 240 VAC) would be easier to install and cheaper to buy (about ($460) but more expensive to operate in most of the US.

1. 
   Kerr | Jan 10, 2002 08:43pm | #2

   *And later, when you pour the new slab, put radiant tubes in the floor.Tim's suggestion will work for you in the mean time if you can install some kind of path for the warmed air to reach each of the "somewhat divided into smaller spaces". Convection might work well enough (a hole at the top and bottom of the dividing walls), or you may add a helper fan in the upper hole to get more flow.The thermal mass of the stone walls will probably make it feel more cool in there than your heated air temp indicates. If you can put some insulation over them that'll help (but stone looks so awesome it is hard to bring one's self to cover it all up!). Maybe you can try one winter without it before you decide about that (after all, that's what sweaters are for).

1. 
   Seth_Frankel_ | Jan 11, 2002 07:53pm | #3

   *Thanks for the great advice. I'll probably go all electric and suffer the higher use costs. I've done a little homework and see that a 7.5 kW model puts out about 23,891 BtuH. Since I know next to nothing regarding heating needs for a given space, do you think this is the best size? I also see models at 3kW (10,239 BtuH), 5kW (17,065 BtuH), 10kW (34,130), and 15kW, 51,195 BtuH). I will probably follow Kerr's advice regarding the fans in the wall for circulation. Where might I find rules of thumb for BtuHs per cubic foot needs? Thanks again.

1. 
   David_Thomas | Jan 12, 2002 03:19am | #4

   *A rule-of-thumb for an uninsulated space with fairly leaky air infiltration (ceiling above, that wooden wall, maybe the stone walls) would be 2 to 3 BTU per square foot of floor space per degree F temp difference.So if your are designing for 20F outside, 70F inside, have 484 square feet, then you'll need (484 x 50 x 2) = 48,000 BTU/hour to 72,000 BTU/hour. I'd go on the high side because you need to get all that rock warm. Not an issue if you keep it warm. But as a shop, you'll save a lot if you turn the heat on an hour before you use it and off again when you leave. In that mode, maybe electrical costs are tolerable. Note that you should confirm that you've got the required amperage at 220 volts (72,000 BTU/hour = 21 kw = 95 amps at 220 volts). And those 95 amps are in addition to whatever you are using in the house.Also check the ratings of electric heater carefully. If it is rated at 240 volts (most are), then you'll need to derate them 16% (i.e. multiple the wattage by 0.84) for 220-volt operation. Not a huge deal, but it may bump you up to the next size unit.What about a wall-mount unit that can converted from propane to natural gas? Run off a portable tank or propane-company-provided tank until you get the natural gas extended. You'll probably have to foot the bill for that extension but in a few areas, the gas company will assist you (cause you'll be using more of their product). And they are cheaper per foot than anyone else. -David

1. 
   Arnold_Griffee | Jan 24, 2002 11:24pm | #5

   *I'm currently building a new shop, my first. standard 8' ceiling is much cheaper but it seems that 9' would be benifical. how important is this issue, should I spend the money? [email protected]