Will a non-dedicated circuit affect the effeciency of an air conditioner window unit?

Question

I have purchased a new 30,000 btu a/c window unit. And yes, this is the proper size for the room. I understand that it should be on a dedicated circuit but I havent gotten around to getting one installed. At this point the unit is plugged in but shares the circuit with some plugs that are not in use. At any rate, when the a/c is running (fan only or cool) our meter spins out of control and our bill went up about $200 the first month of having it installed. Is this a/c faulty or is it the circuit. By the way, my neighbor who has an old unit pays about $65 max during the summer.
Thanks for the input in advance!

30,000-35,000...whatever, it was a round about figure....everyone else knew what I meant.

Answer 1

If you do the math at 24 amps at 120 volts you have 2880 watts. Lets say it is 3000 watts. That is 3 KWH per hour or 72 KWH per day. 30 days is 2160 KWH per month. If you are paying $0.10 per KWH it will cost $216.00 per month of operation if it is running full time.
In terms of being on a dedicated breaker, I am surprised that the unit is running on a 120 volt line. Usually the high capacity AC units require 220 volts. However if you are using a 120 volt feed, then you had better have a dedicated circuit installed with a heavier wire gauge than would normally be used for wall plugs. The AC unit will have the voltage and current requirements printed on the unit. Install a dedicated circuit with a wire gauge suitable for the operating current.

Rule of thumb
15 amps #14 copper wire
20 amps # 12 copper wire
30 Amps # 10 copper wire.

Answer 2

USA I cool three rooms, total 600 square feet, 8 foot ceilings, with one 12K BTU window unit. 30K BTU will cool a huge room. But, if that is the size you need, so be it. Check the SEER rating, which is energy efficiency. The new codes require a minimum of 10, and most mfrs offer 13 or better. The higher the SEER, the lower it will cost to cool the room.

A cooling unit that size should be on a dedicated circuit. If you are operating the unit on an existing circuit that does not have adequately sized wire, you are seriously running the risk of a fire. Pray that the fuse or circuit breaker trips before the fire starts. A licensed electrician can install the proper wiring for you.

As far as your electric bill is concerned, you pay for how many watts per hour that you use. The more watts per hour used, the more you pay. The more hours per day your cooling unit runs, the more you will pay. How many hours per day does the unit operate?30K BTU is a large unit, and uses a lot of electricity. I would use it as sparingly as possible. I don't know what temperature you are trying to keep the room at, but the lower the temperature, the longer the unit has to run. Instead of trying to get the temp down to 72 degrees, go for 78 degrees. When not home, shut the unit off, and pull the shades to keep the sun out of the room. Also, in order to minimize the cooling requirement, insulate the room walls and ceilings to as high an R Value as you can get ( R 30 in the walls R 49 in the ceiling ), and install doors and windows with energy efficient glazing that will reduce the solar heat gain.

Answer 3

A 30,000 Btuh seems way big for a single room. It is clearly running for a very long time during the month and one has to ask if the room is well insulated (or is it a garage with none.) You should be able to judge the usage very accurately by taking readings over a specific few minutes with and without the AC on. The usage of the AC when it is on should match the rating on the plate.
An unshared outlet simply means the unit is not at risk for something else being plugged in on the circuit.
According to one site, a 30,000 unit pulls 2800 watts, which is 23.3 amps at 120 volts or 12 amps at 240 (higher with low voltage). Shared outlets on a 240 volt line seems unusual. If you are pulling 23.3 amps and haven't upgraded from the usual 12 ga. 20 amp wiring, you may have serious voltage losses in the wiring and if you upped the circuit breaker to 30 amp without changing the wiring, you have a serious fire and over heating risk. Also the AC may burn out and will run longer using more power and producing less cool.

Answer 4

If your circuit is dropping that much voltage, then your air conditioner would hardly run, and you'd probably have a fire and/or a tripped breaker/blown fuse by now. I highly doubt you have that great of losses in your line.

Your friend is full of crap and just trying to tick you off, if he is telling you that a 30k BTU unit is going to only draw $65 worth of power in a month. He either lives underground or has R10,000 insulation and never opens his doors or windows.

It is ideal to have an appliance that draws that high of power on its own circuit, but the fact that you DON'T is not the reason your bill is so high. Electricity is expensive nowadays and your unit is a power hog.

Answer 5

your answer is correct in that in the older circuit, there is a lot of inherent internal resistance in the existing wiring, you should have a separate dedicated line just for that unit. the second thing is that 30k btu is huge for a window unit, how big is that room? is the room isolated from the rest of the bldg, or are you cooling the whole house with one small unit??? insulation is important too, the more there is between the room and the outside world is directly relate-able to your electric bill and ultimately your finances. who do you want to have the money in question, you or the utility company? the key is plan, insulate, isolate as much as possible.

Answer 6

A dedicated circuit will take into account the power needs for the unit. You have a circuit that is probally controlled by a 15 or 20 amp breaker. If you're pulling that through a 12-14 ga. wire, it will use more Electricity. Dedicate a circuit using a 10 ga wire and a 20 amp breaker...I believe this will solve the problem, or simply turn the unit to a higher temp so it doesn't run constantly.

Answer 7

OK, here's a brainstorm, may work for you. Take some waxed cardboard or insulation board and make rectangular duct that is shaped to direct the hot air out the window. Use Duct tape on the corners and make sure that the a/c is set up so that the water drains out the window sill. The A/C won't present any chemical hazard because you are just exchanging air. Hope that this helps to keep you cool....

Answer 8

It's because you bought a new 30,000 btu unit. They will suck the power (and money) from ya! Try dropping down to a 20,000 unit.

Answer 9

My esteemed electrical friends...
You pay your power bill by WATTS!!! it doesn't matter if its 120volts, 220volts, 277v. or 480V...U pay by watts..running a dedicated line only prevents an overload condition. Your gonna pay x amount of $$$ whether its 120 or 480..do all the math you want, but thats the final answer...

Answer 10

That is a big window unit, something is wrong. It should have it's own line though.