You are probably asking yourself what size ac do I need in my house if you have called a few companies to give you a quote on a new/replacment unit.  For a few weeks we had a number of a/c companies come out to give us quotes and every a/c company told us we needed something different.  Some of the contractors told us we needed a 3 ton system and others told us a 3.5 ton system.

We had made some improvements to our home with low e impact windows, metal roof, and high insulation in our attic.  Our old unit was about 10 years old and our electric bill had been rising monthly.  So we new we were in need of replacing our old system.  It became a very frustrating process because of all the conflicting information we were receiving from the contractors.

I stopped having estimates and began researching what size a/c system we would need in our home.  How as a homeowner do we know what our home needs.  A unit that is oversized or undersized can cause a lot of issues in the home.  The unit we were trying to replace was no longer running properly in our home. Hence, the higher electric bills.

Oversized units

After researching we started to see that the 3 ton system we had in our home was already oversized and was short cycling.  Basically what that means is the unit is starting and stopping frequently.  This can be caused by thermostat issues, refigerant leaks and the unit being too large for your home.

You want to be careful with the newer units and being oversized in your home because you will not have the humidity control you had with your older unit.  The higher seer more energy efficient units were made with larger coils to cool the home more rapidly.  This is great for cooling the home but it sacrificed the removal of humidity.

You want your unit to be sized properly so you have proper cooling and humidity control.

Undersized units

If your unit is undersized it will have to work harder to cool the environment.  Although, you may not have the humidity issues you would with an oversized unit.  I don’t have a lot of experience in this department.  But, you will lose efficiency with an undersized unit and the system will run longer times.

What about fan speeds

Most newer a/c systems have a way for your contractor to adjust the fan speeds.  Not every contractor does this, we found out the hard way. Not every install is the same and you want to find a competent installer that is properly trained with the equipment you choose.

I will go into this further in another blog post.  Most importantly before choosing a contractor or deciding what size unit your home needs you need to protect yourself and get a third party to complete the calculations to size your unit properly.

Get your home tested and properly calculated

You may be thinking what another expense?  Yes, these tests and calculations are necessary to ensure your system will run with best efficiency, humidity, and temperature control.  After quite a lot of research we learned that it is important to do a manual j on your home prior to having your unit replaced.  New homes have manual j’s completed prior to installation of a new ac.

I will explain why you need this protection in my blog post about what happened to us when we had our unit intstalled after having a manual j.


I have to say that I would never rely on an air conditioning contractor to properly calculate my home.  Why?  A/C contractors should specialize in the installation and/or servicing of a/c and heating.  Their specialty is not sizing air conditioning or proper duct work design.

You can read our story here and please learn from our experience and I am happy that I educated myself as much as I could prior to having our old unit replaced.