When it’s time to install a new HVAC system in your home, a balance must be struck between size, efficiency, and cost. While there’s some flexibility in the level of efficiency you want for your home, and cost is somewhat discretionary, HVAC size is something that’s more static. Discover what’s meant by HVAC size and why it’s important, and then consider a few tips as you evaluate the proper size for your next HVAC system.
What Is HVAC Size, and Why Is It Important?
HVAC size is the amount of heating or cooling capacity the unit has, which is measured in BTUs. BTU stands for British Thermal Unit, and one BTU is equivalent to the amount of heat needed to raise one pound of water by one degree Fahrenheit.
It seems to make sense that a larger unit will heat or cool your home faster, and a smaller unit will simply take longer. From that perspective, it may seem more like a matter of preference than of real consequence.
However, this is far from the reality of how HVAC systems work. The more heating or cooling capacity a unit has, the hotter or cooler it will become at any given time. The size of the unit also determines how much air will move through the system.
If you have a higher capacity unit in a system that isn’t circulating the proper amount of air, it causes problems within the equipment. When you have an oversized system, the unit will short cycle, running in brief but frequent heating and cooling cycles. Conversely, an undersized system will cause the unit to run cycles that are longer than normal. In either case, you’ll consume more energy and add excessive wear to the equipment. This leads to more frequent repairs and a shorter service life.
1. Get Your Home Size Right
The base measurement for sizing an HVAC system is always the size of the space you’re trying to heat or cool. However, many people think that it stops at knowing your home’s area in square feet. This doesn’t tell quite the full story.
First, you need to account for the full serviceable area of your home, which may be different than what’s listed on your real estate paperwork. Rather, you’ll want to consider basements, garages, and attics that may have vents in them, regardless of whether you keep those vents open.
Next, you also need to consider each room’s ceiling height. The normal square-foot allocation per home is based on standard 8-foot ceilings. However, many modern homes have at least one room with a vaulted ceiling. Total air volume is important because it increases how much air the system will have to condition, and it will change the dynamics of heating that particular room.
2. Have Your Ductwork Evaluated
Next, consider the ducts that transfer your conditioned air throughout your home. What you want to look for is older ducts, especially if they are poorly insulated or leaky. In these cases, you’ll need a slightly higher heating and cooling capacity due to energy loss as the air moves through the system.
3. Ensure You Have the Right Insulation
Like your home’s ductwork, its insulation plays an integral part in how your home will transfer heat. Every home will lose some heat through a normal thermal exchange with the air outside. The insulation in your walls, floors, and attic doesn’t conduct heat well, reducing that thermal exchange.
The minimum recommended attic insulation for homes around Glendale is R30. If you’re starting with nothing, this translates into about 10.25 inches of fiberglass batting insulation. R13 is recommended for your floor, which is about 3.5 inches of fiberglass batting installed under your subfloor.
4. Evaluate Your Home’s Construction
There are many other aspects of your home’s construction that will affect the heating and cooling capacity needed. Two of those key factors are your windows and doors. How many you have, their size, and the material they’re made of all play a role. For your windows, there are special films and coatings available that will reduce the amount of heat transfer into your home but may not reduce heat escaping through it. Further, the direction the windows face will also play an integral role in the calculation. In the northern hemisphere, south-facing windows receive the most sun and therefore allow the most heat to come in.
Likewise, your doors are integrally important. Not only should you consider how well a door seals but also what it’s made of and how it conducts heat.
Finally, you’ll consider how well your home is sealed and ventilated. When there is a lot of uncontrolled ventilation, also known as air leaks, you lose a great deal of energy from your HVAC system, requiring it to work harder to keep your residence warm or cool. This will raise the heating and cooling capacity needed from your system and also raise your utility bills.
5. Don’t Forget Your Home’s Orientation
Not only does your window orientation matter, but so does how your home sits on the property. If you have the larger side of your home facing south, it will receive the most sun exposure, allowing more surface area for thermal transfer through that wall, in turn demanding more of your AC. However, if you have a short wall facing south, it presents the least surface area for heat transfer into your home.
6. Consider How Many People Occupy Your Home
Every warm-blooded mammal generates heat, with larger bodies generating more. This plays a critical role in getting to the right HVAC size and is often neglected. Not only do you want to consider the people who normally reside in your home, but also how frequently you have guests. Count any pets as well, especially large ones.
You needn’t consider the occasional guest who may stay for a few hours. However, if you have regular guests, that generally increases the maximum number of occupants in your home for sustained periods, and you should factor it in. This is especially true for anyone running a home business, a yoga studio, for example who has employees or customers coming over. While it may not affect your heating needs much, it will have a significant impact on the AC capacity required.
7. Review Your Heat-Generating Appliances
Now, consider your home’s heat-generating appliances. The obvious ones include your oven, stove, and clothes dryer. However, you’ll also want to consider your dishwasher, refrigerator, and any freezers in areas served by your HVAC system. Be sure to also consider high-powered electronic equipment such as gaming computers or computer servers. These all produce significant heat that pumps into your home, and that will affect the cooling equipment you need.
8. Examine Your Home’s Sun Exposure
Finally, examine your home’s sun exposure beyond which direction the house faces. The primary factor here is the amount of shade your home receives throughout the day. If it’s in nearly complete shade all day, you’ll need less cooling capacity, but may need some additional heating capacity. Conversely, if it’s in more full sun all day long, you’ll need more cooling capacity to keep up when the Arizona summers reach their peak.
For more than 40 years, property owners around Glendale have trusted Christian Brothers Air Conditioning Plumbing Electrical whenever they needed home services. Our team of experts provides everything from heating and air conditioning installation, maintenance, and repair to indoor air quality solutions, duct repair, and a wide range of residential plumbing and electrical services. For more information on sizing HVAC equipment, call to schedule a consultation with one of our NATE-certified installation technicians today.
