Is it true that even though a central heat & air unit may run 24/7, it's NOT using MORE electricity?

Question

My central heat & air unit is a little too small for my house (my landlord finally admitted it, but doesn't feel that its enough of a difference to have it changed it). This causes it to never get to the exact temperature needed & stay long enough for the unit to cut off. I'm concerned that my electric bill is going to be sky high. My landlord assures me that because it's a smaller unit, it is actually going to use much less power. That even though it never shuts off, that doesn't mean it will run my power bill up. Is he right or is he just saying that to get me to shut up (for now)?

Answer 1

Yes, if everything is working correctly and both systems are operating at the same efficiency, then he's right. In fact, you should use LESS electricity than if you had a larger system running intermittently.

This is because less power is required to operate a small system than is required for a large one, and because a certain amount of energy is wasted each time the system starts and shut down. The wasted energy is mainly due to the need to build up high pressure in the condensor of the system when it starts up and the unused cooling in the evaporator when the system shuts down.

However, if your system is running all the time, it could wear out sooner. In addition, this could be as sign that it is working inefficiently due to a problem and needs repaired.

From US DOE:
Proper sizing and installation are key elements in determining air conditioner efficiency. Too large a unit will not adequately remove humidity. Too small a unit will not be able to attain a comfortable temperature on the hottest days. Improper unit location, lack of insulation, and improper duct installation can greatly diminish efficiency.
http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12350

Answer 2

One thing you might want to consider is this:

When a A/C unit start up, the first 15 minutes or so of the run-time is VERY in-effecient. Most units take about 30 minutes to enter into a mode that unit is designed to achieve.

The reason behind this, is that it is working to pull the moisture out of the air, rather than cooling the air. Water droplets form on the evaporator coil, reducing the contact surface area between air and the coil. Therefore, if the unit is way TOO BIG and cycling every few minutes, it will never reach the most effecient mode of operations.

In fact, A/C industry suggests a too small of a unit is better than too large of a unit. Too large of a unit uses more power to run and never reaches the most effecient mode.

What I am concerned, in your situation is not the fact it is running 24/7 but how effecient it is running. One of the things you can do is to measure the temperature of the air going into the intake and measure the temperature of the air coming out of the register. Then calculate the difference.

This difference of tempearture is called DELTA-T in the industry. The standard is 20 degrees.

If it does not reach this tempearture, ie. value is too small, that means either the unit is ineffecient or air volume (fan) is too high. If it reaches above 20 degrees, then the fan is too slow, filter is clogged, or the inside is clogged with dust.

Keep in mind, a/c unit does require regular maintenance.

I will tell you though, when outside temperature reaches 97F or higher, mine never shuts off, and that is what it is designed to do. In my area, the design temp for summer is 95F. That means, the whole system is designed to run 100% of the time when the outside reaches 95F and inside is set to 78F (I think). I set my t-stat to 81F inside.

What you can do is to compare your power bill with that of your neibhbors. If yours is way off and you are setting the thermostat at a reasonable level, you may have a reason to be concerned.

Good luck.

Answer 3

Of course it's going to run up yor bill, but that doesn't mean it would cost anything more than if you had a larger unit. A larger unit will cycle on and off more often, but it would cost more to run while it was on.

He is right, but he is wrong. If he bought you a properly sized high efficiency unit, then you would save on your electric bill, but he is not concerned about your electric bill. He only cares about the rent. He is not going to spend money so you can save money.

Answer 4

He is wrong. If the unit is constantly cycling it is going to cost a lot to operate it. It will use less power than a bigger unit that cycles constantly but a unit should not keep cycling. In the heat of the summer I turn my unit to . The fan running uses 110v which is cheaper than having your 220v condenser cycle all the time. My electric bill went down 10-15% when I left the fan on.

Answer 5

You are right! He's just pulling your leg! The smaller the unit, the more it has to run and therefore the more energy/electricity it will use! If the proper size unit is used then the thermostat control keeps it from running all the time, it will only kick on when needed, therefore, using less energy/electricity! I don't know what to tell you as far as making him change it, you could always threaten to move. I'm not sure if you can accomplish anything from calling your local fair housing for tenants or something to that effect. I would sure try though, tell him that if he's not going to change it or pay 1/2 your electric bill, then you are going to notify your local fair housing board.

Answer 6

Your landlord is F.O.S. If the unit was not undersized it would cycle on and off more frequently and not run all the time. The longer it runs - the higher your electric bill. His lies will not pay your excessive electric bill! Tell him to fix it or you'll move out, and you will expect to be somewhat reimbursed for your excessive electric bill..............

Answer 7

i know when i run my central air 24/7 i get a bill around 300.00 and suting it off and turning it on does use alot more. i would check into that if i were you before you get a huge bill.