Having the right-sized HVAC system for your house is absolutely essential. Both undersized and oversized HVAC systems can create many issues. It will typically lead to your heating and cooling bills being far higher and your home never staying as comfortable. Below, we’ll take a look at the different factors that determine what size HVAC system a house needs and also the process that HVAC technicians use when sizing a cooling or heating system.

Calculating Square Footage

The first step in determining what size HVAC system your home needs is to calculate the total square footage of the conditioned space. The conditioned space refers to the living area, or whichever rooms and areas are connected to the HVAC system. This includes the living room, kitchen, bedrooms, and bathrooms, but not the attic, garage, or crawlspace since these areas are generally never conditioned.

If you’re unsure of what the total square footage of all your home’s living areas is, then this will need to be calculated before moving on to determine what size HVAC system is needed. This is done by measuring the length and width of each room, and then multiplying the two together to determine the room’s square footage. You can then add up the square footage of each room to calculate the total square footage.

The heating or cooling output of all HVAC units is measured in BTUs (British Thermal Units). Once you know the total square footage, you can then move on to determining how many BTUs your HVAC system would need to produce per square foot. However, it’s important to understand that the recommendations for BTUs per square foot are based on a house with standard eight-foot ceilings. If your home has high ceilings in some rooms, this will also need to be taken into account. The higher the ceilings are, the greater the air volume is, and the more BTUs will be required to heat or cool the space effectively.

Determining How Many BTUs Are Needed Per Square Foot

Exactly how many BTUs an HVAC system needs to produce to heat or cool a home depends on where you live. This should be fairly obvious, as people living in northern climates will need much more heating due to the cold winters. At the same time, people living in warmer climates like Arizona won’t need as powerful of a heating system but will need many more BTUs of cooling since the summers tend to be very hot.

The US Department of Energy splits the country up into seven different climate zones, and there are specific BTU recommendations for heating and cooling in each zone. Gilbert and the Phoenix area are in climate zone 2. In this zone, the general recommendation is that you need somewhere between 35 and 40 BTUs of heating per square foot. With air conditioning, the recommendation is somewhere between 45 and 50 BTUs of cooling per square foot.

It’s important to note that these are just general recommendations and may not apply to every home. This is because there are numerous other factors that can directly influence how many BTUs an HVAC system needs to produce to heat or cool a house efficiently and effectively. For instance, the BTU requirements are typically lower for newer homes than they are for older buildings, as newer houses tend to be much better insulated and have a tighter sealed exterior structure. Older homes are typically not that well sealed, which means they have more gaps in the structure where heat and cold can seep inside and also where the hot and cold air from the HVAC system can leak out.

The level of insulation and how well-sealed the structure is are just two of the many factors that can influence how many BTUs are needed to heat and cool effectively. This is why it’s always essential that you have a certified HVAC technician calculate what size HVAC system your residence needs. When sizing an HVAC system, technicians use a special formula that doesn’t just look at square footage and climate zone but instead adjusts for all the other important factors. In this way, you can be assured that your new air conditioner, heat pump, or any other unit is exactly the right size for your home and will be able to cool or heat effectively without using more energy than necessary.

The Importance of Having a Manual J Calculation Performed

Most HVAC technicians use something known as a Manual J calculation when sizing any heating or cooling system. This process is also known as a load calculation, and it takes into account all the various factors that can influence how much heating or cooling is needed. The process starts off by measuring the total square footage of all the conditioned areas in a home.

After measuring the square footage, the technician will then evaluate the house’s level of insulation and various other factors that can influence heat loss or heat gain. This includes how well-sealed the exterior envelope is and how much direct sunlight or shade the building receives throughout the day. A property that receives lots of direct sunlight will usually need a larger cooling system and a slightly smaller heating system since it will get lots of daytime heat gain from the sun.

The number and size of all exterior doors and windows in residence is also an important factor since windows and doors are some of the biggest sources of heat gain and heat loss. The general rule is that you need to factor in an additional 1,000 BTUs for every exterior door and window in the home. That being said, the location of the windows is also important. Houses with lots of north- and west-facing windows will typically need a larger cooling system since these windows will let in lots of light and heat during the hottest parts of the day.

How many people live in the building also needs to be taken into account. The technician will even take into consideration appliances like ovens, water heaters, dishwashers, washing machines, and dryers that produce heat. You typically need to factor in an additional 100 BTUs for every person in a household. The technician also needs to calculate how much heat is produced by all of your appliances. For every 12,000 BTUs of heat produced by appliances, you would normally need to increase the size of the AC unit or heat pump by 1 ton, as 1 AC ton equals 12,000 BTUs.

After performing all of these calculations and taking all of the different factors into account, the technician can then much more accurately determine how many BTUs your HVAC system needs to produce. Performing a Manual J calculation is far more accurate than simply estimating BTU requirements based on square footage and climate zone.

If you don’t have a Manual J calculation performed, there’s a high chance you could end up with a unit that’s either too small or too large for your home. Both oversized and undersized units will use far more energy, have a shorter lifespan, and simply not heat or cool as effectively. That’s why it’s essential that you have a Manual J calculation performed before installing any new HVAC unit.

At A/C Doctors, we install a wide range of HVAC units, including central air conditioners, heat pumps, gas and electric furnaces, and ductless mini-splits. When you choose us, you can be assured that our team will calculate exactly what size of unit you need so that you don’t end up with something that’s too small or too large to work effectively. For more information on our HVAC installation services or to schedule any residential or commercial heating, cooling, or indoor air quality service in the Gilbert area, contact us today.

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