Choosing the correct size air conditioning unit is a frustrating and confusing proposition for many homeowners. Getting an air conditioning unit that is too big or too small can reduce your comfort, increase operating costs, decrease efficiency, and even lessen the lifespan of your unit. Even when you get price quotes from multiple companies, you will likely get recommendations and rationales for various size units. The following guidelines will give you important insight into the process of sizing air conditioning units. Your HVAC company will use a formula called the Manual J Residential Load Calculation to determine the optimal size for your air conditioning unit. This involves a rather complicated calculation using a number of variables, including: Your home’s construction materials. The number of windows. The size of the rooms. Your home’s insulation levels. Or, click here to request a air conditioning replacement quote online. Fortunately, you can get a close approximation using a much simpler formula.

You can get an estimate of the required tonnage of your air conditioner by dividing the square footage of your home by 600. Do not include the square footage of your basement or garage in the calculation. The following is an example: Square Footage of Home/Size of AC Unit 1,500 sq. ft./2.5 tons (1,500/600) 1,800 sq. ft./3.0 tons (1,800/600) 2,100 sq. ft./3.5 tons (2,100/600) 2,400 sq. ft./4.0 tons (2,400/600)outside ac unit is not working Greater than 2,400 sq. ft./5.0 tonshow much does a new air conditioner unit cost 2012 It is important to keep in mind that new, energy efficient homes may require a smaller unit depending on the home’s particular style, construction, and orientation.how much electricity do ac units use

Your heating and air company will do the long-form load calculation to fine tune the size of your air conditioning unit; however, your rough estimate should be within about one-half ton of the actual size. You should be wary if your heating and air company recommends a unit that is more than one-half ton smaller than your calculation. If this happens, you should advise the contractor to make sure there is sufficient air return for the extra cooling capacity. You should also ask for a written money-back guarantee in case you are not satisfied. Another way to determine the appropriate size air conditioner is to look at your existing unit. The unit’s capacity is coded into the model number of the unit. For example, if your air conditioner’s model number is CKL18-1, it is a 1.5-ton unit. The number 18 indicates that the unit is 18,000 BTUs. There are 12,000 BTUs in one ton; therefore, your unit is 1.5 tons. The following is a handy conversion guide: Number of BTUs/Number of Tons

It is important to ensure that you are looking at your air conditioner’s model number and not the serial number. Many homeowners make the mistake of getting an air conditioner that is too big for their home thinking that it will cool quicker or be more efficient. In fact, getting a unit that is too large will cause the system to short cycle. This means that the compressor will not run long enough to dehumidify your home. The unit will cycle on and off more often, which will reduce the life of your system and increase operating costs. Types of Central Air Conditioning Units When selecting a central air unit, you have the choice of installing the entire unit outside of the home or installing the compressor and condenser outdoors and the blower or evaporator indoors on the furnace. The split configuration is the most economical. This allows the furnace blower to deliver the cooled air throughout the house through your existing air duct system. Choosing a Window Air Conditioner

If you opt for a window air conditioner over a central heat and air unit, the first step in selecting the right size unit is to determine the square footage of the area that you want to cool. To do this, you multiply the width of the room by the length. For example, a 10-foot by 10-foot room would be 100 square feet. You can then use the following guide to determine the appropriate BTU rating for your unit: 150 to 350 sq. ft./5,000 to 8,000 BTUs 351 to 550 sq. ft./8,000 to 12,000 BTUs 551 to 1,050 sq. ft./12,000 to 18,500 BTUs 1,051 to 1,600 sq. ft./18,500 to 25,000 BTUs Certain conditions may decrease or increase your particular cooling needs. For example, a heavily shaded room may require less cooling. You may need a larger unit if it is to be located in the kitchen, if the room gets a lot of direct sun, or if the room is normally occupied by multiple people. Contact us today if you are in need of a reliable heating and air technician in the Denver area.

Our professionals look forward to helping you with all of your heating and cooling needs. Or, click here to request a air conditioning replacement quote online.A question I pose to the attendees of each mini split class I conduct is: Can you oversize an inverter ductless mini split system? Before you start writing your reply to what I’m sure you think is an obvious answer, let me save you the effort — yes — the answer is yes, of course you can! Gerry Wagner’s testing lab for Comfort-Aire mini split products.   Now, with that out of the way, let me address why I pose the question at all if it’s so obvious. We need to start with the anatomy of an inverter system. An inverter compressor can run at 3,600 RPM like every other compressor in HVACR equipment, but the difference is that it doesn’t have to. Let me digress a moment… I'm a “wet-head” by birth. Being from the New Jersey and New York area, hydronics is the first HVACR subject you learn about, and then air comes later.

When I started in the boiler biz back in the 1970s, we made a lot of different boilers: 50,000 Btuh, 75,000 Btuh, 100,000 Btuh, 125,000 Btuh, 150,000 Btuh, and on and on. Today boiler companies, for the most part, make one boiler, a modulating boiler that can down fire to as low as 50,000 Btuh and modulate up all the way to 150,000 Btuh. If you install this boiler in a home with a heat loss of 100,000 Btuh it doesn't short-cycle because it will never produce anything over 100,000 Btuh. Because it measures indoor and outdoor ambient air temperature and fires the boiler accordingly. Now you can take that old, oversized non-modulating 150,000 Btuh boiler, in a home with a heat loss of 75,000 Btuh, and stop it from short cycling by adding indoor/outdoor reset to the control system. Instead of heating the water up to 180°F even when the outdoor temp is 50°F and you just need to take the chill off, the control will fire the boiler only up to the temperature required to meet the heat loss of the home based on the outdoor air temperature.

There would be some mechanical changes required, specifically a bypass from the boiler supply to the return to make sure a minimum return temp came back to the boiler to prevent thermal shock. New condensing boilers don't require a bypass as the lower the return temperature the more efficient they run. So why am I giving you the Hydronics 101 lesson? Well, because the same principle applies to an inverter compressor. Wagner conducts a course sponsored by Comfort-Aire and Heat Controller Inc.   The inverter compressor does not start at 3,600 RPM and then ramp down as the system finds the set point programmed by the homeowner. It starts at the lowest RPM and ramps up. If the actual room temp and the setpoint are only a few degrees apart, then the compressor will never come anywhere near full capacity. Like the modulating boiler, the inverter system senses both indoor and outdoor temperatures and applies power to the compressor accordingly, (the compressor is the burner, if you will).  

The test lab I can prove it very easily. My test lab here in New York is a 10-ft. x 20-ft. prefabricated garage where Itest mini split products on a consistent basis with multi zone and single zone inverter systems, both cooling and heating. . . This building contains radiant floor heating, (slab on the first floor, joists on the second), with a Pulse condensing boiler and a small duct high velocity air conditioning throughout. [Wagner’s home is also heated via radiant flooring, a thermal solar system for domestic hot water, and an oil fired boiler is used as the heat source, plus, small duct high velocity for air conditioning.] A recent equipment test had me install a single 12,000 Btuh inverter ductless system in the lab. Rather than short cycle as you would expect, what happens is the system rarely shuts off. The compressor will initially, (over a three minute period, if needed), ramp up to full capacity and get the room to the programmed set point and then you will see the compressor ramp down to a minimum running RPM.

If the fan is on auto, it will do the same. The compressor may shut down completely and the controls programmed into the equipment will keep the compressor off for a minimum of three minutes and then it takes another three minutes for the compressor to come back up to full capacity. A minimum cycle (if it existed) could be no shorter than three minutes. Inside the lab two 9K evaporators are tested. You can further increase the run cycles by placing the evaporator fan in the manual mode and operating it at the lowest speed. What always has to be considered when dealing with inverter ductless mini splits is the range of operation that the system will provide. Unlike a conventional system that only knows two performance points, on and off, the inverter offers a range of performance. A 9,000 Btuh inverter evaporator will give you an operating performance range of approximately 2,000 Btuh to 11,000 Btuh of cooling. A 12,000 Btuh inverter evaporator will give you an operating performance range of approximately 3,000 Btuh to 13,000 Btuh of cooling.

An 18,000 Btuh inverter evaporator will give you an operating performance range of approximately 7,000 Btuh to 23,000 Btuh of cooling. Two ways to oversize Let’s look at an example. If you install a 9,000 Btuh inverter evaporator in a room that has a heat gain of 5,000 Btuh, will it ever produce 9,000 Btuh? It will ramp up to 5,000 Btuh and satisfy the set point programmed by the homeowner and then maintain that set point thereafter. So, with this in mind, back to my original question: can you oversize an inverter ductless mini split system? Well, I believe there are two ways to oversize utilizing an inverter mini split. The first is the obvious capacity oversize. Let’s use the same example of a room with a 5,000 Btuh heat gain. If you install an 18,000 Btuh inverter evaporator in that room, are you oversized? The low end of the performance range of an 18,000 Btuh inverter evaporator is 7,000 Btuh — more than the total heat gain of the room. Where I see installers make a less obvious mistake in sizing inverter mini splits is with this scenario.  

Again, the room with the 5,000 Btuh heat gain, but now we have an installer who decides to install a 12,000 Btuh evaporator in the room saying to himself, “It’s an inverter, it won’t ever go up to 12,000 Btuh because the room only needs 5,000 Btuh … so what’s the harm?” Under normal conditions the unit will never go beyond 5,000 Btuh, but the harm is that his competitor who makes the more accurate choice of a 9,000 Btuh evaporator for the same room will get the job based on equipment cost alone!  Keep in mind, that the appropriate 9,000 Btuh evaporator will still allow an additional 6,000 Btuh of capacity beyond the room’s calculated heat gain of 5,000 Btuh should your customer decide to have a keg party in the room on the 4thof July and invite all his or her sweaty friends! I’m a believer in inverter mini splits for so many reasons, in so many applications, but we still need to use our skills to make sure we are choosing the right equipment for each application. Gerry Wagner is an instructor for ESPCO Inc. Gerry has 32 years in the HVACR industry and conducts classes throughout the U.S. and Canada on related subjects.