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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have 3.5 ton AC 2014 sq ft two story house in

Customer Question

I have 3.5 ton AC for my 2014 sq ft two story house in Houston. Some companies said I have to have 5 ton AC or it will be over loaded. Some companies said I have to stick with 3.5 ton AC or the existing duct will not take any larger AC. I am confused.
I look online and find 4 ton AC is fine. My questions are: (1) What ton should I choose. (2) If I use 3.5 ton AC, will it wear out my AC (3) They said 3/4 duct and 7/8 duct. How I find out what is mine? (4)If I have 3/4, can I use 4 ton AC. (5)If I choose
4 ton AC and use existing 3/4 duct, will the coil get frozen due to low flow? (6) My goodman AC last 16 yr. But they said current goodman AC is compressing motor that last only 5 year, trane uses other technoloy and last longer. Is it right? Thank you very
Submitted: 2 years ago.
Category: HVAC
Expert:  airheatman replied 2 years ago.
1.To begin with, the only way to be sure unit is sizes properly is to do a load calculation on the home.THis is known as a Manual J Load Calculation.It is a program where you enter all of the building construction factors such as square footage of home, construction type such as wood frame or brick,how much attic insulation, wall insulation. whether on a slab or up off the ground on peers. the square footage of glass windows and type of windows facing each direction, whether there are covered porches shading windows,number of occupants(figuring 2 per bedroom),number of fireplaces if any, number and type of exterior doors,ceiling types,geographic location and other such factors.For example a 1500 square foot well insulated home with double pane windows on a slab with 8 foot ceilings and very few windows facing east and west (receiving direct sunlight) with 2 bedrooms in North Carolina with an average high summer temperature of might 85 require only a 2 ton unit to properly cool the home where as the same1500 square home in South Alabama with an average high of 95 degrees.with 9 foot ceilings or if not well insulated and had a lot of glass windows facing west or east may require as much as 3 tons to properly cool the home.2.Once load calculation is done, you do not want to go more than 1/2 ton above and definitely not below that size.3.Not sure what they mean by 3/4 and 7/8 ducts, Can you provide more details?4.If they are referring to refrigerant pipe size, you will need 7/8 on any of systems listed5.Small refrigerant lines will result in improper cooling6.All manufactures have improved technolgy. Goodman is currently one of the leaders in technology.Both Goodman and Trane have excellent warranties of at least 10 years7.Do not allow yourself to ne mislead by Trane sales pitch.
Customer: replied 2 years ago.
Thank you very much for your answer. I want to clarify that the copper pipe line for my current 3.5 ton AC is 3/4" dia. Can I live with 3/4" if I choose 4 ton AC? The copper line is within the brick wall. It was put in when the house was built. Is it possible to replace it? Thanks.
Expert:  airheatman replied 2 years ago.
The 3/4 is really too small for even the 3.5 ton with the new equipment,Manufacurers recommend minimum of 7/8 . If possible can you perhaps run new tubing up wall and cover with a vinyl cover designed for this?
Expert:  airheatman replied 2 years ago.