Soil Heat Cables did work well for us this winter. We harvested our lettuce and spinach several times during the winter without heating the GH. We placed the heat cables 4"s under the soil in a 30" x 8' area - then covered the area with polycarbonate sides and lid - creating a heated grow box. Much less expensive than heating the entire GH! I have moved most of our Geranium starts to the GH grow box now to make room for our tomato starts under the indoor grow lights and the Geraniums are loving it. Here is a photo taken in December when inside GH temperatures reached as low as -2 degrees: The soil heat cable is on a thermostat set @ 55 degrees. Even though we will continue to use the GH grow box in years to come during the cold winter months - we are installing a GH heater this year to maintain the temperature in the GH to approximately 50 degrees starting in the late March - April time frame to get an early start in our GH. The daytime temperatures on sunny days is already up to 100 degrees when not vented. The cost to heat the entire GH to 50 degrees at this time of year will be very inexpensive - especially when compared to the winter months! We are installing a propane GH heater with blowers as soon as the weather permits and I can get the concrete walks and heater platform poured. This post was edited by Hudson...WY on Tue, Mar 5, 13 at 10:05

Okay, so I supplied you with the numbers and the assumptions that got to those numbers. It's possible that some of the assumptions (like the cold water temp) is wrong... but what we designed for was 3 gpm (slightly more than a shower) and 50 degree temp rise. The heater to do that has a max draw of 100 amps. That's all math. You may only load a circuit to 80% of its rated capacity. That's code. Now, if you are able to run this heater on a 200 amp service depends on the rest of your power usage. You have 60 amps left to work with. It's borderline. Patricia Colwell Consulting is not correct. An electric tank heater and an electric tankless heater are both almost 100% efficient at heating water. An electric tank heater has standby losses of about 3% in normal usage. The issue is that any tankless heater must heat water very quickly. That requires a lot of energy over a short amount of time. For that reason, both gas and electric tankless require very large inputs. For example, my gas tankless heater is 200k btu/h which is twice as much gas input as my furnace. There is no magic here at all. You can do the math yourself - 1 BTU = the energy to raise 1 pound of water 1 degree F. Water is 8.34 pounds per gallon - so it takes 8.34 BTU to raise a gallon 1 degree F or 1251 BTU per minute to raise 3 gal of water 50 degrees in one minute or 75,060 BTU/hour. There's 3412 kw per BTU/hr so that's about 22 kw (the heater was a 24 kw model- so slightly higher). dadoes is correct - this heater isn't going to be running at 100 amps all the time. However, you do have to design it for the times that it will run at maximum capacity (when someone is taking a shower and the inlet water temp is 50 degrees)

Following just to see what the answer is! When it comes to electrical problems, the answer will vary. This is a forum board in which everyone throws out a guess like change the breaker it's weak or defective in some way. Could you be right, yeah. But often times the guess is wrong. You have to understand electrical flows are like water & air in that they take the path of least resistance. (water when it's confined to a pipe -- if the pipe is plugged where is the path of least resistance?) If you have resistance in a live wire and that live wire touches ground somewhere you have a short to ground, however because there is resistance in that wire it's not a direct short. So the resistance in that wire becomes a load. That is how electrical fires start --- that won't necessarily trip a breaker. Using the same example -- but changing it up a bit that live wire 120v lets say -- touches another live wire of 120v say this other live wire is the other leg that feeds the panel, just a brush will trip that breaker main more often than not. Typically it will blow things apart pretty violently, so it's unlikely to repeatedly do it and you certainly do not want to be no where near it if this were to occur. Think about loosing fingers and possibly your eye sight and maybe even your life. If two live wires of the same leg were to touch -- nothing would happen. Realize this is 120v hot --- touching the same leg 120v hot. If you put a meter to each of these legs the meter would read what? ( your hands are not volt meters) It's not uncommon for rodents to get in and chew things, they shouldn't. Usually high end power as in 120v & 240v enclosures are typically well sealed from that possibility. BUT, until you inspect it -all you can do is guess. Guessing and electricity is dangerous. That is why there are 'licensed' electricians. Class dismissed.

Your more cost efficient way is stick to gas. If the electrical wiring isn't up to the job your cost jumps way up. My advice is to update the gas wall heaters if you wish since your worried about cost and if you're paying the heating bill stick with gas.