The proper size HVAC system depends on a number of factors, so bigger is not necessarily better. The bigger the unit, the more energy it consumes, if the unit is undersized then it will need to work much harder and will not produce enough air. It is very important that you have the correct size unit for your application

The size or capacity of your Air Conditioning system is measured in tonnage (which is not weight) and BTUs (British Thermal Units). A British thermal unit is a measurement of the energy it takes to raise one pound of water one degree. Often the power level of an HVAC unit is determined by the BTU. Tonnage essentially refers to how many BTUs it will take to properly service a home. For example, the capacity of a system is measured by ton. One ton is 12,000btu.

How Do I Know What Size System I need?

If you are replacing like for like, the simplest method is to look at your data panel on your existing outside unit. There are very long letters and numbers. There should be a distinctive 2 digit code (usually between #12-60 ) embedded in the string of letters and numbers. That number divided by 12 will yield your tonnage:

18 = 1.5 tons
24 = 2 tons
30 = 2.5 tons
36 = 3 tons
42 = 3.5 tons
48 = 4 tons
60 = 5 tons

Essentially, there are 12,000 btus for every ton of equipment. The code 18= 18,000 btus divided by 12,000 btus (1 ton) equals 1.5 ton. This is helpful when replacing like for like units.

Obviously though, the only way to truly tell for certain what proper size unit you need is to contact your HVAC professional. There is a complicated equation that allows for the total square footage of the building, geographic region, general temperature ranges and allows for a calculation for each window, door, insulation and occupant. A home might require a different tonnage if there have been changes such as:

• Adding a new room or space
• More, or less occupants
• Improving insulation, energy efficient windows, door seals

These scenarios can affect the capacity needed from your HVAC equipment.

Estimated HVAC Capacity

Some examples of what proper size HVAC and air conditioning unit is needed for the following sized homes:

In this case, a 1500 sq’ home requires 80,000 btus to properly cool efficiently and would require a 2 ton unit.

As already mentioned, these are loose examples only and someone would need to take many calculations in order to properly size a system.

In Conclusion

It is very important to have the proper size HVAC system for your home and needs. Air Doctor Heating and Air provides Free Estimates if you are considering a new system and we will make sure it is the proper size system for you.