Heating the Shop

Stacy, you've pretty much got it. I'll have my woodstove going most evenings and get a good fire going before heading in for the night. So the fire should keep it warm most of the night and the heater can just maintain. I think I'll get a couple of the heaters to try it out for now.
The 3 windows have covers to go over them on the inside so that should help. Thanks for all the input guys!
 
Don't plug electric-resistance heaters into the same power source or circuit. You have two phase legs in your garage, you can at most plug in two heaters without decreasing your heat output and driving up your electrical draw at the same time.

They are not additive.
parallel-resistors-w.gif
 
You are applying the formula wrong for the situation. The formula needed is I=E/R . Your formula will calculate the total resistance of the three heaters on the wiring, which is only part of the equation. The output of each heater does not change.
The voltage (E) is fixed.
The resistance of R1-2-3 is fixed. The reciprocal resistance ( 1/Rsum) is lower, as you pointed out, but still fixed.
Thus the current ( amperage) goes up when you add another heater to the circuit.
The two fixed quantities do not change.

Think of it this way - In many homes, all the lights on one floor are the same circuit. If the theory you posted was true, all the lights would get dimmer every time you turned another room light on.


The shop wiring will deliver as much current as is needed for the heaters up to the limit of the breaker. The current draw is additive, and thus you need to consider how large the wiring and circuit breaker size is before plugging in several heaters in the same circuit. Each heater will still draw 1500 watts individually, and deliver 5000BTU of heat. There is no loss or gain. The same rule applies to running motors on 120 or 240VAC. The total power consumed is the same, you save nothing. The gain is that you draw half the current per line, so you can run higher powered motors on a 240 circuit than a 120 one ....using the same wires.

It would be best to plug the heaters into different breaker circuits both for keeping the breakers/wires cool and not overloaded, as well as a fail safe in case one heater kicks out a breaker. The other(s) will still be on.

Had to grab a note pad:
Each heater is 1500W which at 120V means the resistance is 9.6 ohms.
three in parallel combine to create a resistance of 3.2 ohms. Thus one heater on a circuit draws 12.5 amps, two draw 25.0 amps ( the max for a 30 amp circuit), and three would pop the breaker.
 
Last edited:
bladsmth said:
You are applying the formula wrong for the situation. The formula needed is I=E/R . Your formula will calculate the total resistance of the three heaters on the wiring, which is only part of the equation. The output of each heater does not change.
The voltage (E) is fixed.
The resistance of R1-2-3 is fixed. The reciprocal resistance ( 1/Rsum) is lower, as you pointed out, but still fixed.
Thus the current ( amperage) goes up when you add another heater to the circuit.
The two fixed quantities do not change.

Think of it this way - In many homes, all the lights on one floor are the same circuit. If the theory you posted was true, all the lights would get dimmer every time you turned another room light on.


The shop wiring will deliver as much current as is needed for the heaters up to the limit of the breaker. The current draw is additive, and thus you need to consider how large the wiring and circuit breaker size is before plugging in several heaters in the same circuit. Each heater will still draw 1500 watts individually, and deliver 5000BTU of heat. There is no loss or gain. The same rule applies to running motors on 120 or 240VAC. The total power consumed is the same, you save nothing. The gain is that you draw half the current per line, so you can run higher powered motors on a 240 circuit than a 120 one ....using the same wires.

It would be best to plug the heaters into different breaker circuits both for keeping the breakers/wires cool and not overloaded, as well as a fail safe in case one heater kicks out a breaker. The other(s) will still be on.

Had to grab a note pad:
Each heater is 1500W which at 120V means the resistance is .104 ohms.
three in parallel combine to create a resistance of .035 ohms. Thus one heater on a circuit draws 12.5 amps, two draw 25.0 amps ( the max for a 30 amp circuit), and three would pop the breaker.
Click to expand...

That's way too low resistance, .104 ohms would blow the breaker as it is basically a direct short. Resistance is voltage / amps.

I actually calculated 0.1 ohms out to 144000 watts and 1200 amps!
 
Last edited:
bladsmth said:
You are applying the formula wrong for the situation.
Click to expand...

I wasn't formulating anything. Just pointing out that if he plugs them into the same circuit he will pay more, and get less heat.

The resistance of the circuit is only a guess. there are many different heating elements, and metals used in them which result in varying resistances between heaters.
 
Good catch, I think I hit divide on the wrong number. R=E/I so 9.6ohms= 120V/12.5A . I changed it.

In any case the output is still 1500 watts per heater. He will pay twice as much in electricity for two heaters and get twice as much BTU output.
 
Just curious, but what in the shop can't handle below freezing temperatures? It might be cheaper to just heat that stuff, instead of the whole shop. Finishes, glues, etc could be kept in an insulated cabinet, or old fridge body, heated by a light bulb or small heater coil
 
Mahoney said:
Just curious, but what in the shop can't handle below freezing temperatures? It might be cheaper to just heat that stuff, instead of the whole shop. Finishes, glues, etc could be kept in an insulated cabinet, or old fridge body, heated by a light bulb or small heater coil
Click to expand...

Me

Especially when every metal item you touch sucks the heat out of your hand so it shrivels and seizes into a twisted claw

straight out of Edgar Allan Poe's imagination.
 
Two space heaters is not going to heat that shop when the woodstove goes out for any length of time when temperatures go into the -20s or -30s. They may hold the shop briefly overnight if the woodstove is lit first thing in the morning. However, there are going to be situations when the shop isn't going to be used over a period of days, and portable electric heaters are not going to cut it. I'm not a fan of electric heat due to its cost, but those 220 volt construction heaters mounted on the cieling would be a better choice and far safer.

Concider the distance your shop is from the main feeder from the house and what gauge is the main feed line. You may have voltage drop issues when running electric heat, as it takes a great current to run them, and if the wiring is undersized they could be running warm or worse pose a fire hazzard. Space heaters are a good as temporary measure, but concider propane or oil heat for winters in Mn, which is not much different from my location just to the north of there.
 
2 oil filled heaters keep my shop just fine in that kind of weather.
 
Ah...now I see

Whether or not you will be able to keep the shop warm with an electric heater or two will depend on how well insulated and air sealed it is.

Do you have any thermal mass near the wood stove, i.e. bricks or stone slab on the wall behind it, etc...? Thermal mass will release heat slowly through the night and help to keep the shop warm.

Over the long term more insulation will be less expensive than more heat. Does the insulated shop share a common slab floor with the uninsulated portion? If so, that's going to be a challenge.
 
Mahoney said:
Ah...now I see

Whether or not you will be able to keep the shop warm with an electric heater or two will depend on how well insulated and air sealed it is.

Do you have any thermal mass near the wood stove, i.e. bricks or stone slab on the wall behind it, etc...? Thermal mass will release heat slowly through the night and help to keep the shop warm.

Over the long term more insulation will be less expensive than more heat. Does the insulated shop share a common slab floor with the uninsulated portion? If so, that's going to be a challenge.
Click to expand...

Insulation is money burnt once.
 
Grinders, anvils, vises-anything with metal and mass take a very long time to heat to room temperature.
And, heating/cooling to extremes creates condensation. Condensation equals rust. I have found that keeping the shop at a minimum 60 degrees in the winter works well, and it doesn't take too long to raise the temp to a comfortable 70 degrees plus. Insulation is a very good thing-both in winter and summer.
 
Insulation is your friend. I live in a custom built house with heated garage and shop. I used to use the shop to breed reptiles, but I am cleaning that out to make it into my mechanics garage and knife shop. I have 5000sqft to heat here in the Canadian winter. We have extended periods to -20c to -40c. My house is very well insulated, with R80 in the attic. I have spray in insulation in all exterior walls, and many of the exterior walls are 8"thick. My basement is R50 Styrofoam insulated, and all widows are triple glazed. During the coldest months, my heating bill is $300.00 to $375.00. My geothermal heat pump broke down a couple winters ago over the Christmas break, and the house stayed warm for 4 days before the service team got out and fixed the problem. The airflow in the house is 1/3 what a current spec built house for this area is. I have to have mechanical ventilation because of this.
 
Mr. M said:
So, my lovely bride and I bought a small piece of land and a shop with a house also on the property :D
I am trying to decide the best way to keep the insulated section of the shop just above freezing. The shop is 26'x72' and the insulated section is 18'x26' that I want to keep warm.
I have a woodstove in there that I use when I'm out there so it doesn't need to be able to get it real warm, just 38 degrees or so.
I don't have gas on the property but if a gas heater will be the best I can look into that.
What suggestions do you guys have?
Click to expand...

they make camping propane heaters. you get a propane 20 pound tank like you can buy at ace hardware and then you need to find the head that fits on top of the tank and you have a heater. I bought the small one o it was only a 15,000 BTU heater. now they make bigger heads that have a much higher BTU rating.
 
Willie71 said:
Insulation is your friend. I live in a custom built house with heated garage and shop. I used to use the shop to breed reptiles, but I am cleaning that out to make it into my mechanics garage and knife shop. I have 5000sqft to heat here in the Canadian winter. We have extended periods to -20c to -40c. My house is very well insulated, with R80 in the attic. I have spray in insulation in all exterior walls, and many of the exterior walls are 8"thick. My basement is R50 Styrofoam insulated, and all widows are triple glazed. During the coldest months, my heating bill is $300.00 to $375.00. My geothermal heat pump broke down a couple winters ago over the Christmas break, and the house stayed warm for 4 days before the service team got out and fixed the problem. The airflow in the house is 1/3 what a current spec built house for this area is. I have to have mechanical ventilation because of this.
Click to expand...

I need to stop complaining about $80.00 power bills
 
I've burned about 4 cords so far, the retrofit has paid off with the new foam board insulation and siding on the house, and have would have been up to 5 or 6 without it. I have burned less than a 1/4 tank of furnace oil due to the cold weather my wood furnace does not get a chance to go out.
 
Coldest winter here in 25 years! Wood stoves in the shop and house have been great. No money spent on heat... :D
 
richard thurman said:
they make camping propane heaters. you get a propane 20 pound tank like you can buy at ace hardware and then you need to find the head that fits on top of the tank and you have a heater. I bought the small one o it was only a 15,000 BTU heater. now they make bigger heads that have a much higher BTU rating.
Click to expand...

MH24T-1.jpg




They do throw lots of heat, but they consume lots of air.

I've co poisoned myself with that - sweaty, pale, naseauted, dim witted.
http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning

Even a cracked window or door may not be enough, but you sure notice the heat lost with opening to the outside.



Get a vented ceiling mounted propane heater.
mr.heater2.jpg


There is a price difference.
 
You must log in or register to reply here.
Back
Top