Installing an HVAC system that is either too small or too large for your home is a massive waste of money. Having an undersized or oversized HVAC system will almost always lead to issues that make it more difficult to keep your house warm in winter and cool in summer. You’ll also have to pay more for heating and cooling than you would if your system was correctly sized. Another concern is that you’ll usually need to have your HVAC system repaired more frequently if it isn’t the correct size. All of these reasons are why it’s essential you have an experienced HVAC contractor determine what size you need when it’s time to replace your heating or cooling system.
Common Issues With Undersized and Oversized HVAC Systems
An undersized system will struggle to provide enough heating or cooling except on fairly mild days. With a properly sized HVAC system, each heating or cooling cycle will normally only last for 15-20 minutes. On the other hand, an undersized system could easily run for at least an hour at a time. In Florida, the high heat and humidity can even result in days when an undersized system runs continuously and only finally shuts off much later in the evening. The increased number of hours the system has to run each day is one of the main reasons why undersized systems almost always have a much shorter lifespan.
One reason your energy bills will be higher with an oversized HVAC system is that a larger system has a higher energy demand. The other reason is that oversized systems usually have issues where they continually short cycle. Short cycling is when the system only runs for a few minutes and then turns on again fairly soon after shutting off. That means the system ends up performing many more cycles per day than it normally should. HVAC systems draw far more power when cycling on. The more times the system cycles on each day, the more energy it uses. All of the motors in an HVAC system are also under much more strain when cycling on. As a result, they suffer more wear and tear, which is why oversized have shorter life expectancies as well.
Factors That Impact HVAC Sizing
The two most important factors when sizing an HVAC system are the square footage of the home and the local climate. Square footage obviously matters since the larger the house is, the more air the HVAC system has to heat and cool. Climate is equally important since a house in Florida obviously has much higher cooling requirements and much lower heating requirements than a house in Michigan or Montana.
The type of HVAC system can also sometimes make a difference in what size it needs to be. This is especially the case with heat pump systems. In Florida, you’ll usually need a larger heat pump than you would in some other parts of the country. That’s because you need to ensure it’s capable of handling the high heat and humidity and can keep your home sufficiently cool. A house in a place with much colder winters would also need a larger heat pump.
Two other important factors are the age of the house and the level of insulation it has. If your house was built before the 1970s or so, your HVAC system will likely need to be at least a bit larger than it would if your house was built in the past few decades. Old houses often aren’t that well-constructed, resulting in their structures being fairly leaky. Air leaks mean the house loses quite a bit of heat during the winter and heats up faster in the summer. That’s why the HVAC system usually needs to be bigger to ensure it can keep up with the extra heat loss and heat gain. Newer houses made with modern building materials are usually built better, meaning they have better insulation and far fewer air leaks. You can often get away with a slightly smaller HVAC system since there’s less work it has to do.
How Professionals Size an HVAC System
To accurately determine how large of an AC, heat pump or furnace a house needs, HVAC technicians use a special process known as a Manual J load calculation. This calculation determines the building’s specific heating and/or cooling load and how many BTUs of heating or cooling the HVAC system has to produce to effectively meet this load.
The first part of the calculation determines the square footage of the house. The technicians only look at the conditioned living areas the HVAC system supplies and not anything like an attached garage or attic. If the entire house has standard-height ceilings, they’ll just use the square footage. If some or all of the room has higher ceilings, they’ll instead look at the cubic footage. The higher the ceilings are, the greater the volume of air there is that needs to be heated/cooled.
The calculation has general recommendations on how many BTUs of heating/cooling you need in different climate zones. The average recommendation is 20 BTUs per square foot. However, 20 BTUs of cooling per square foot will generally never be sufficient in Florida. Instead, you usually need something like 40 to 55 BTUs per square foot to ensure the AC or heat pump cools effectively enough. An older house that’s poorly insulated and/or has a leaky structure will typically be at the higher end of this range, and a newer house will often be at the lower end.
These initial calculations give technicians a baseline number to start with. They’ll then begin adding or subtracting from this number based on a variety of different factors. One important factor when calculating cooling requirements in Florida is the total number of windows the house has. Windows can add to a building’s cooling requirements because of the additional increase in heat the house gets from the sun shining through the windows. The general recommendation is that each window increases the cooling requirements by 500 BTUs. However, it depends on the direction that the windows face, as you get very little heat gain from north-facing and east-facing windows. Whether much of the building receives direct sunlight during the hottest parts of the day also has a big impact on how much additional heat it experiences.
The cooling requirements also increase based on the number of people that live in the house as a result of the heat people’s bodies continually give off. As with windows, the general rule is that each person adds an extra 500 BTUs to the cooling requirements.
Once technicians have determined the specific BTU requirements, they’ll then be able to calculate the required tonnage for the AC or heat pump. One ton is approximately 12,000 BTUs. ACs and heat pumps are available in half-ton increments from 1 to 5 tons. If the BTU requirements are right on the borderline, it’s always best to round up to the next highest unit. That means if the calculation determines the house’s cooling requirements are close to 36,000 BTUs, technicians will likely recommend a 3.5-ton, 40,000-BTU unit instead of a 3-ton unit. That way, you can be certain the unit will be able to keep up on extremely hot or overly humid days.
When it comes to HVAC installation services in Auburndale, FL and the surrounding areas, Snowbird Heating & Cooling is the company you can trust. We install all types of heating and cooling equipment and will perform the necessary calculations to ensure your new system is the right type and size for your home. We can also assist with all your ductwork needs.
To get help with choosing the right replacement HVAC system, contact Snowbird Heating & Cooling today.
