6000 Btu Air Conditioner

How a pro contractor installs a portable air conditioner that is most efficient

There is a natural tendency for people, especially Americans, to always opt for the biggest and most efficient AC they can possibly afford. The prevalent calculation is, the more efficient the A/C unit, the better it will work. It will cool the room faster, and thus not affect your energy bill.

Not necessarily.

A pro knows what homeowners forget. In this instance, the best air conditioner should be selected for the room it will be placed in.

Under many situations, the btu, or cooling power of the unit is directly proportional to the size of the room. But where homeowners start to go astray. This is true only in perfect, or ideal, conditions. In other words, this assumes good to excellent insulation in the walls, a good newer window that will be sealed and has a good insulation value. Placing an A/C unit in less than ideal conditions makes you change the original estimates given on the sticker.

For example, a 5,000 btu room A/C with a 9.7 EER rating may advertise it will effectively cool approximately 1500 square feet efficiently. This is about a 15x10x10 room. That's assuming 10 foot ceilings.

So you naturally buy the unit for a 15x10 room in your dwelling, and it fits fine in the window, but it doesn't appear to be operating as efficiently as you'd like. Why is that the case? What could be wrong?

Simply put, the insulation or window insulation may not be as good as you thought.

The easiest way to determine whether or not an air conditioner will cool your room is with the heating estimator calculator in the Home Energy Audit Kit. It makes the calculation easy - all you do is give the dimensions of the room and "guestimate" the insulation. This is a critical step that homeowners always miss - but HVAC contractors never do. Insulation is in your walls to minimize the heat transfer. The better the insulation, the less heat is lost.

So, let's go with the assumption that our room is 15x10x10. Furthermore, let's assume that the air conditioner we want is about 85% efficient (so its not a high efficiency energy star model) and the average temperature outside is 85 degrees F. We want it to be a cool and comfortable 76 degrees F in the room. And lets pretend our insulation is just average.

Entering the info into the calculator, we find that at its most efficient state, the air conditioner would have to output 6728 BTU, or about 34% more cooling power than the unit we bought can possibly provide. Therefore, the window unit we have isn't acceptable.

Let's assume we select a 93% efficient model, or an energy star one. Our btu requirement goes down a little to 6260. That's still relatively inefficient for our needs.

As you can see, there are a couple of culprits here. The first is the insulation. Average insulation is reducing overall efficiency by about half in this instance. We know this because if we adjust our insulation rating to "excellent", and keep everything else constant, our BTU need falls to 3130 - so under our conditions, the 5000 btu air conditioner most likely will work fine.

The next problem is the "bad" information on the unit. You should always assume the manufacturer's ratings for room size to be under ideal conditions.

So now you're wondering "Well how can I improve the efficiency of the air conditioner?" Unfortunately, you can't improve the efficiency of the A/C directly, but you can change the temperature of the thermostat. In fact, increasing the temperature of the room to 78 degrees F, and keeping everything else the same gives us a completely different result. Now, we need 5233 btu for an 85% efficient unit, and 4869 btu for a 93% efficient unit. These are completely different than the 6000+ btu we needed before.

Keep in mind you can also circulate the cooled air with a ceiling fan. Drawing shades will help - and keeping the door to the room closed of course.

There are a few lessons to learn from this experiment. First, now you can understand why modifying the thermostat on your air conditioner is not a good idea, unless you adjust up the temperature - the cost for running the unit increases notably. You also can see how vital good insulation is, and why finding the volume of a room before you go to the store is so necessary. HVAC contractors always make these measurements and calculations before going to the warehouse, and then choose the top, most efficient model in a price range that will efficiently cool the room.

David Andersen is a home energy expert and is currently researching energy efficiency techniques. David is a firm believer in homeowner education and energy conservation. He is the owner of a free home energy saving blog, with exclusive valuable information no homeowner can be without ==> http://www.utilitybillbusters.com

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