A/C System Sizing

Using the Square Footage ‘Guess’

The problem with using floor area to ‘guess’ air conditioning and heating load capacity is EVERYTHING. Using square footage to guess air conditioning load capacity doesn’t take into account any of the relevant factors like: Attic insulation … Size and location of windows … Single pane vs. double pane windows … Ceiling heights … Floor and wall insulation and construction.

Using this method doesn’t take into account what temperature YOU want to keep the house or any unique circumstances. It usually leads to oversized air conditioning and heating systems that are more expensive to install and much more expensive to operate.

seer table

This chart shows just how expensive this ‘short cut’ can be in the San Marcos, Kyle, Buda, and New Braunfels area. A ½ ton air conditioning sizing mistake on a 3 ton 13 SEER system will cost $121.00 a year. A one ton air conditioning system sizing mistake would add an additional $2,420.00 in utility costs over 10 years.

Replacing Your Air Conditioning and Heating System With The Same Size System

Since 70% of current air conditioning systems are already oversized, this is a real good way of duplicating an existing mistake. Guessing air conditioning Btu capacity off the tag on the outside unit only estimates system nominal cooling capacity. When selecting HVAC equipment, it’s critical that the actual manufacturer’s specifications are taken into consideration.

The few minutes a contractor shaves off the price of a new air conditioning system by ‘guessing’ can be added to the additional saving shaved off other installation short cuts to get you a lower up front price. But you’ll end up paying much, much more over the long haul.

a house

A Whole House or Room by Room Heat Load Calculation

This is by far the most accurate method of sizing your HVAC system. With the right equipment it takes about an hour and with the right contractor it shouldn’t cost anything. Running a heat load calculation on your home takes into account the size of the rooms, number and type of windows and the direction they face, insulation in the attic and walls, type of foundation, location of doors and supply vents, and more.

Running a Heat Load is Only the Beginning

Today’s higher efficiency heating and cooling systems run with warmer evaporators. This means they’re not as efficient at removing moisture from the air. This makes correct equipment sizing more critical than ever to maintain indoor comfort levels.

If you oversize higher efficiency air conditioning system, the house may reach the set air temperature too quickly. Interior wall, furnishings, and ceilings will still be putting off a lot of heat causing the system to cycle on and off too quickly. This wastes a LOT of electricity and doesn’t allow the system to operate long enough to reach ‘steady state operation’ where most humidity removal takes place.

ACCA guidelines require a Manuel J load calculation to calculate load and Manuel S guidelines to select the right heating and cooling equipment configuration to match the needs of both the building and the occupants.

If you live in the San Marcos, Kyle, Buda, or New Braunfels area, give us a call and ask to schedule a heating and air conditioning system replacement analysis. I will come and perform a full room-by-room heat load calculation and show you equipment from several different manufactures. It’s easy, no pressure and the best part: it’s FREE. CALL (512) 392-0022