Thinking about installing a new air conditioning and heating system in your home? First things first, this is not a DIY project, leave this for the professionals to do. Improper installation from someone that has not had proper HVAC training and certification can lead to cracked drain pans, failed compressors, poor air flow, not getting the full capacity out of you unit, and much more. Plus in most States a permit is required to install a new heating and air conditioning systems if it’s the split system type.
Picking out a New Split System Air Conditioning
Don’t go cheap. Some of my favorite brands are Rheem, Carrier and Lennox. My personal opinion is to keep it simple. The more controls and features you have, the more that can go wrong. It’s a personal choice though, if you want a super-efficient air conditioning system that has small computers built into the Thermostats, then be warned there are more than likely going to be problems. And good luck getting someone to actually fix the problem.
Another tip for the home-owner, don’t purchase a R-22 unit shipped with dry nitrogen. R-22 is going to be history soon, and the prices for the refrigerant aren’t getting any cheaper as costs for r-22 recently doubled. Get a r-410a system and you should be in good shape for the next 10 years or so.
Pre-HVAC Installation Checks
Is the line set efficient for the size of the unit? According to manufacturing specs line sets must be properly sized from the beginning. If a line set is too long, or has too many elbows and 90’s in it, you are just increasing the pressure drop of the refrigerant. Same applies is the line set is undersized from the beginning. For instance if you are putting in a 4 ton unit and have 150 foot of 5/16th for the hot gas/liquid line, you are never going to get that unit to put out 4 tons of cooling, no matter how much you think you have the charge right or airflow right.
Another good reason to switch to 410a system from R-22, is that 410A is much more forgiving for line sets that are too small and too long. What isn’t acceptable pressure drops for a R-22 system may be acceptable for 410a systems. To determine this you will need a pipe fitting book to get the right specifications.
Do I Have to Change Line Sets when Installing a 410a System?
Not necessarily. The only time that this would be necessary, is if you had a line set that ran under ground, and determined that it was leaking with a isolation leak test. Or if the line set was undersized and the specifications fail the acceptable pressure drop. Other than that the line set would have to be blown out with dry nitrogen and properly evacuated when the new system is installed.
If you are replacing your air conditioning system because of a compressor burnout, then if you can you may want to replace the line set as well. Just because a compressor burns out and contaminates the line set, doesn’t mean it can’t be cleaned and reused, it’s just that it’s a little harder to clean even with the help of acid away and a suction line drier. Like I said if this is the case, and if you can, replace the line set in this scenario.
Get a Heat Load Calculation Done on Your Home
The person that is quoting the job to replace the air conditioning system should be doing a heat load calculation to see how big of a unit(s) you are going to need to cool your home. Heat load calculations include many factors such as total square footage of the home, ceiling height, window types, which direction the windows face and how big they are, attic insulation type, along with several other factors.
If your system is undersized you are going to be running the unit more than it needs to be running, and it may not be able to keep up with the heat transfer from the outside heat on a hot day.
If your system is oversized you are going to cool the home down too quickly and may not properly remove the humidity the home.
For residential applications a heat load calculation is usually referenced by Manual J.
Do I Need New Duct Work for My New Air Conditioning System?
This all depends on the shape that the old duct work is in, whether it has multiple leaks, and whether or not you have enough return and supply duct for the unit. For instance a 20” supply duct is good for approximately 1600cfm, given that there the distance and angles are within specs. Residential Duct sizing should be done using Manual D.
Overlooking the duct work can cause you big problems. If your duct work is undersized problems like mold may form at the supply trunks and also inside of the air handler, no matter how many UV lights you have installed in the system! Undersized duct work can also create so much static pressure that it sucks the water off of the evaporator coil into the duct work, causing much more problems such as water leaks and bacterial growth within the air conditioning system.
As you can see there is a lot more that goes into residential HVAC installation than just swapping out the same ton unit with a newer one. When getting a new air conditioning installed do your homework on the contractor and reviews that they have had, and if you are an installer or estimator, you should make sure that you know Manual J and D for residential applications.