Inept handyman repair of air conditioners
Can’t a handyman fix my air conditioning system?
the guy that caulks your windows and paints the trim on your garage is not qualified to work on your air conditioning system. If you hire him to work on your air conditioning and he screws it up, very likely, then it’s your fault. You should know better than this.
I’m not knocking handymen here. they are very useful for those odd jobs around the home. In fact we actually have one who is properly licensed and insured and we use him to repair those problems that occur from time to time on jobs that we perform. Occasionally one of the workers will put his foot through a ceiling or will scratch a wall. We are human and things do happen from time to time.
The problem with ducting air conditioning system
Ducting is the other major loss in a new installation. It gets hot in the attic and many service technicians choose to ignore the ducting because of that. It turns out that the majority of ducting in homes here in Southern California is undersized. There is a very good reason for it. The Uniform Mechanical Code only sizes ducting for heating-not cooling.
The UMC states that the size of the ducting need to be 2 squares of free air movement for every 1000 btus of heating. That means that 75,000 btu heater needs a round duct that is equal to or greater than 150 squares of cross sectional surface area. Using pi (area of a circle) we find that a 14 inch duct is 3.14 x 7 x 7 = 153 square inches. More than big enough. Well a 75kbtu furnace can have up to a 4 Ton drive blower (48,000btu of cooling) and cooling btus require 6 square inches of free air per every 1,000 btus of cooling. 48 x 6 = 288 square inches of cross sectional surface area. Using pi again we find that the minimum duct size to operate that 4 Ton unit is 18” ducting. Ducting only comes in even numbered sizes above 10 inch in diameter.
If your ducting is choking down your air system, you are paying for air conditioning that you are not receiving. A Ton of air is between 350 and 450 cubic feet of air per minute. The ideal in this area of the country is close to 400 cubic feet per Ton. Areas with higher humidity use a smaller amount of airflow and areas of desert use closer to the 450 cubic per air figure.
Virtually every study ever perform on heating and cooling btu loss in ducting has concluded that about 35% of all wasted btus in a heating and cooling system come from undersized, broken, restricted or improperly installed ducting. Have your ducting checked out every year and save a bundle on utility bills as well as increasing your comfort ratio.