Air Conditioning: What’s it about?

It’s all about “AIR!”

First, your home’s air conditioning system must be sized correctly to provide the proper CFM of air and BTUs of cooling to each room of your home.

What is CFM?
CFM (Cubic Feet per Minute) is a measure of volume of airflow rate. Visualize a basketball. A basketball is approximately 1 cubic foot in volume.

How many CFM’s does your system require?
For example, a typical 3 ton system (36,000 BTUs) requires a minimum of 1,050 CFM to a maximum of 1,200 CFM to perform to manufacturer’s specifications.

What are BTUs?
(British thermal unit) – 1 BTU is equal to the heat produced by burning a single wooden match or can be defined as the amount of heat required to raise the temperature of 1 pound of water by 1°F.

Once you have the proper airflow, you can cool it, heat it, dehumidify it and clean it, to provide you and your family with total personal comfort.

Bedroom airflow issues
How to know if it is a lack of supply air or lack of return air:

FIRST: Does the room cool fine during the day with the entrance door open?

SECOND: Is your problem only when the door is closed for privacy issues?

THIRD: If the room cools satisfactorily and only has issues when the door is closed, add a properly sized return air grill with duct work ran back to the air handler plenum.

FOURTH: If cooling is not adequate with door open, increase airflow supply, enlarge supply duct or add additional supply register with accompanying duct work coming from supply air plenum, plus add a return grill with accompanying duct work ran back to return plenum for good performance.

NOTE: The new building code requires all major rooms to have properly sized return air grills to allow free flow of return air back to air handler.

It’s NOT the Heat – It’s the Humidity! How do you control it?

True home comfort is when your air conditioning system provides your home with acceptable humidity control and comfortable temperature, all while performing quietly.

What is acceptable humidity control? – When your home’s humidity is under 50% with the ultimate goal to be in the 42% to 45% range.

How to Control Your Humidity: 

1st) An accurate load calculation (a computer program that calculates your home’s exact cooling and heating BTUH requirements) MUST be performed. Please! No rule of thumb, guessing or just replacing with the size you presently have. This will lead to a poor performing system and unacceptable humidity control.

FACT: Today’s single speed air conditioning systems under perform older systems in humidity control by upwards of 30%. This is the result of Federal Government Department of Energy intrusion in the engineering of air conditioning systems, mandating higher efficiency with no consideration for those who live in a subtropical environment. For engineering information to show the results of this intrusion on your Southwest Florida Home, click here.

Note: An air conditioning system can only remove humidity when it is running, therefore an over sized unit will not  remove moisture sufficiently, due to short run times.

FACT: Every time your system comes on it takes up to ten minutes of run time before it will start to do any significant dehumidification in your home. Therefore the first ten minutes is mainly  producing only what is termed “sensible cooling” which lowers the homes temperature and satisfies your thermostat. Your system may shut off before any significant dehumidification is obtained, and if your system is over sized this just magnifies the dehumidification problem.   

2nd) The best product on today’s market for True Home Comfort is a full Variable Speed System. This product is designed to vary the speed of both the indoor unit and the outdoor unit to provide you with the humidity level and the temperature you desire. Upon start up both the outdoor unit’s compressor and the indoor unit’s fan varies in speed to maximize the humidity removal from your home.

FACT:  An outdoor unit running at a higher speed and the indoor unit running at a lower speed will allow the indoor coil to get to a much lower temperature, enabling an increased amount of dehumidification to occur.

What is YOUR comfortable temperature setting? – Comfortable temperature varies with most people, therefore move your thermostat setting as high as possible to keep your home comfy. The higher you can set your thermostat, the less power consumption. Therefore, lower electric costs. To see the relation between your home’s humidity and temperature, click here for your personal comfort.

What is quiet running performance?:  – No noise should be heard from your indoor unit. Most noise from your indoor unit is usually caused from a poorly designed and installed duct system, causing extreme strain on your indoor blower motor. Besides the objectionable noise, premature failure of your indoor blower motor is assured. The next area of objectionable noise is from the air distribution system; this could be in both supply and also return grills. Undersized grills or lack of the number needed to provide quiet operation. Duct systems that are undersized will also cause unwanted noise levels.

Humidity Control Settings

For YOUR Florida Home:

You live in a sub-tropical paradise, which means your home’s humidity level must be controlled for your personal comfort.

The first step is very critical. Your air conditioning system must be sized to a very close tolerance in order to control the homes humidity, keeping you personally comfortable, protecting your health and your furnishings, and lowering your power bills.

You probably have heard advertising or had companies promoting “whole home dehumidifiers”. These are needed usually because the air conditioning system was never sized properly for your home. An over-sized system has no ability to control your humidity personal comfort.

  While away on Vacation:

The tried and true method to control your homes humidity while you are away for extended amount of time is by a programmable thermostat, programmed to run for only two hours per day. (Schedule to call daily for cooling at 70 degrees from 5AM to 7AM–all other schedules set to 90 degrees, 2 hours of run time is all you need.)

This schedule maintains good control of your relative humidity and is a recommendation from the local power companies.

Florida Power and Light recommends this humidity control method and schedule:

Cost to operate $:

Since you have set the air conditioning system to only operate for 2 hours per day your monthly energy cost can be calculated.

Example of cost: A base 13 seer 3 ton system requires approximately 3 KW of power at standard design conditions. Therefore, 3 KW times your power company’s cost per KW of 10 cents approximately equates to- (3KW x 10¢ x 2 hrs. per day = 60 cents per day). Therefore, your cost to control your homes humidity while you are away will be approximately $18.00 dollars per month.


    Example: Program a call for cooling at 5 am daily with a temperature request of 75 degrees at 7 am set temperature back to 90 degrees. All other programmable settings to be set for 90 degrees. The home only needs two hours of run time per day.

Tested home at these settings- maintains a relative humidity between 45% to 55% and a temperature range between 75 degrees to 83 degrees.

Old technology (dehumidistat): The goal was to keep your relative humidity (RH) at approximately 65% RH.

New technology (programmable thermostat): Set at the above time frame, testing, proves better relative humidity (RH) control with an average of 52% RH and a monthly power bill that is constant. Come back to a fresher, drier home.

If this was MY home, I’d choose 50% RH.

How to Properly “Charge” your AC System

The following is a quick overview of procedures needed to properly charge your air conditioning system:

Refrigerant charging might be the least understood practice in the air conditioning industry next to the number one problem–airflow!

Tools needed to do the proper job:

  • Magnahelic Differential Pressure Gauge (to verify the correct airflow)
  • Refrigerant gauges (that have been calibrated)
  • Accurate thermostat probes (that have been calibrated)
  • Superheat charging charts
  • Temperature split charts

The following procedures are a MUST:

  • All coils, filters and blower wheel must be clean
  • Airflow must be known within manufacturer’s specifications
  • Outdoor temperature must be above 60 degrees and indoor above 70 degrees
  • Indoor wet bulb temperature must be known
  • Once the charge has been adjusted, waiting 15 minutes to verify accuracy of adjustments


Mold and Your Air Conditioning System

A well trained air conditioning contractor is your indoor air quality (IAQ) specialist when addressing cooling, basic filtration and ventilation for your home. But when it comes to air particle testing, taking mold samples, biological identification, mold remediation or health issues, you should look to a specialist for help. These tests are outside the licensing and expertise of a typical air conditioning contractor.

At what point can mold become a threat? Mold has been called “Mother Nature’s reclaiming process.” Mold spores are literally everywhere. A typical healthy house is host to tens of thousands of mold spores. The problem begins when mold spores find an environment where they can reproduce exponentially. Mold needs moisture to grow. Control the moisture and you can control mold growth. Good housekeeping keeps it in check, the problem is often easily cleaned up.

In rare cases mold can be caused by your air conditioning system due to lack of maintenance, clogged or leaking drain lines etc. These air conditioning related causes can usually be corrected by a qualified air conditioning contractor.

Beware of scare tactics from a service person when he/she tells you how ‘mold infested’ your system is. This is referred to by air conditioning contractors as “black gold.” (Money-makers!)