Why Do I Need a Manual J Load Calc?

So you’re planning on getting a new HVAC system! But you’ve heard that most new homes nowadays have an HVAC system that is way oversized. And although there is an old saying “Bigger is Better!” you know that’s not always true. So, what about your HVAC system? Does size really matter? Yes it does!! 

If you get an oversized cooling system it can result in:

  • Muggy air inside because the system does not run long enough to dehumidify
  • A shorter system lifespan due to frequent turning on and off, called “short-cycling”
  • An installation cost that is more expensive than necessary

So, what can you do? How do you decide what size system is just right for your house?

Well, unfortunately, most HVAC contractors rely on general rules of thumb to determine what size of cooling systems to install. True HVAC load calculations require time and attention to detail and most contractors don’t bother. Instead, they generally calculate a system need of one ton for every 500 to 600 square feet of floor area. But just like no two thumbs are alike, neither are any two houses exactly the same. Even a house with the same floorplan as another but rotated 90 degrees could have a difference in its cooling load of 25% or more.

However, here is where "Manual J Calc" can help. The Air Conditioning Contractors of America (ACCA) developed a protocol called “Manual J” as a way to correctly determine the size of a cooling and heating system. Using these load calculations will correctly determine the actual cooling needs of your unique home.

In the old days these calculations were done by engineers with pen, paper and a slide rule, which is why contractors came up with their own rules of thumb. However, now there are computer programs which can do the calculations even right at your home. First all relevant data must be collected: the home’s orientation, insulation levels, window types, areas of all the surfaces that gain or lose heat, and more. The Manual J HVAC load calculation will then calculate the cooling and heating needs of your home in terms of Btu per hour for each room and the house as a whole.

Nowadays, newly constructed homes are calculated on average to need 1 ton of cooling for each 800 square feet of floor space (not the contractor’s typical rule of thumb of 500 to 600 square feet per ton). And some high performance homes can get as 1,500 to 2,000 square feet per ton. So a contractor using 500 square feet per ton will be installing a system that is way oversized – two to four times larger than it should be – resulting in a humid house, shorter system lifespan and unnecessary expense. Even the ENERGY STAR new homes program requires no more than 15% oversizing of cooling systems to qualify. There is absolutely no reason to install a system that is 200-400% larger than it needs to be!

The professionals here at GAMA Air are trained to use the Manual J protocol. We want your new system to be precisely what you need right here in Beverly Hills, Culver City, Mar Vista, Miracle Mile, Hollywood, West Hollywood, Los Angeles, West Los Angeles, Santa Monica, Marina Del Rey, Pacific Palisades, Brentwood, Bel Air, Westwood, Downtown Los Angeles, Vernon, Huntington Park, Sherman Oaks, Encino or the surrounding area, not what Joe Blow over in our neighbor state needs. We can not only suggest equipment adequate for your home but also give you a room-by-room load calculation, and even design a duct system for maximum efficiency of your new system.

If you would like more information on how we can help you with your up-coming project to replace your heating and cooling system, please give GAMA Air a call at (310) 651-6936 or use our online form to request a free visit with no obligation.

If you wish more information, simply click here: Ask An Expert.

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