Determining the Best Size HVAC System for Your Home

February 2, 2022
HVAC Sizing in Roseville, MI

It’s important to get the right size HVAC system for your home in southeast Michigan. Having the wrong size will cost you dearly and will leave you uncomfortable throughout the year. As you evaluate your HVAC system options, consider why size is so critical and how to properly calculate your need.

HVAC 101

Before looking at how to calculate the size of the system you’ll need, it’s essential to understand how HVAC systems work. Whether you’re talking about heating or air conditioning, the same principles apply.

Heating and cooling start with heat transfer, either moving heat into or out of your home. To make your home cooler, your HVAC system conditions the air moving through the system, which then circulates into your home. This process changes your home’s air temperature until it’s at your comfort level. The furnace works in the opposite direction, warming the air and pushing it around your home. Without the right amount of heat transfer or the right amount of air circulation, your home will never achieve the right temperature.

The Importance of Proper Size

Whether you’re talking about an oversized or undersized system, both equally prevent even and efficient heating. An undersized system typically means there isn’t enough heat transfer taking place. When this happens, your system runs excessively long heating and cooling cycles.

At the other extreme is an oversized system, a problem that may seem like it should be beneficial since it would offer more heat transfer than needed. However, when you have an excessively oversized system, it heats and cools too quickly. The result is the system running cycles that are too short, leading to less air movement and more frequent cycles.

Both undersized and oversized systems increase your overall operating costs, leading to higher utility bills than when your system runs appropriate cycle lengths. They both also add strain to the system, increasing the frequency of repairs and shortening your system’s service life.

HVAC Size Measurements

When talking about HVAC size, most people are referring to the amount of heat that the system can transfer. As for furnaces, it’s the amount of heat it produces whereas air conditioners and heat pumps refer to heat absorption and transfer.

The British thermal unit is the common unit of measurement for HVAC systems, also referred to as BTU. A single BTU is the amount of heat required to raise one pound of water by one degree Fahrenheit. You may also see systems sized in tons, where one ton simply equals 12,000 BTUs.

Since your system relies on its ability to circulate air, the other size consideration is the volume of air it’ll circulate. Cubic feet per minute or CFM is the common measurement for air circulation volume in HVAC systems.

Most furnaces have a circulating fan built into the unit rather than relying on a separate air handler. In these cases, the manufacturer ensures that the volume of air that the fan will circulate matches the heating capacity of the system.

Some systems rely on a separate air handler, such as a heat pump. In this case, it’s critical to ensure that your system can circulate enough air to properly heat and cool your space.

It’s not only the specs of the system that matter, either. Your home must have the proper ductwork installed to handle the volume of air the system will move. If there isn’t enough cold air return in the system, it’ll strangle the system, preventing effective heating and cooling in addition to damaging the system.

When a professional works to size your system, they are accounting for the needs of your home, which we’ll discuss below. However, they’re also considering your current infrastructure and its effectiveness for the current needs of your home.

Starting With Home Size

Your home’s size is the foundational measurement for determining the best size HVAC system for the home. When we think about the size of your home, we don’t actually mean the livable space that’s commonly reported in real estate listings. Rather, it accounts for all the space the system serves.

One method for calculating your home’s serviceable square footage is to measure the exterior of your home and to multiply the length by the width. This works well for most homes, which are either square or rectangular. Multiply this figure by the number of floors that your HVAC system services.

You’ll want to account for any area the system doesn’t serve, including areas like attached garages. Calculate the square footage of those rooms, and subtract that amount from the total.

However, if you have a split-level or irregularly shaped home, this method may not work as well. In these cases, simply go room by room and calculate the square footage; then, add it together. Be sure to include areas that aren’t necessarily rooms, such as hallways, closets, pantries, and entryways.

Double check your attic, basement, and garage to ensure there aren’t vents ducted to those areas. If there are, include them in your calculation even if you don’t commonly heat or cool those areas.

Considering Regional Climate

Once you have the area your system serves, you’ll need to convert it into the initial BTU size you’ll need. The climate for your area determines the conversion rate you’ll use. Southeast Michigan is in Climate Zone 5, which requires between 50 and 60 BTUs per square foot served.

Multiply your square foot calculation by this conversion rate, and you’ll have the starting point for your capacity requirements. There are additional considerations that’ll adjust your system size up and down, so you’re not quite done yet.

Adjusting for Heat Sources

The number of people who occupy your home is also a key factor in sizing your system and not just because it keeps them safe. Each person produces heat, so you have to account for that increase in temperature when considering HVAC size, especially with air conditioning.

In addition to the people who reside at your home, it’s important to consider how you use your home. For instance, if you frequently have groups of people over for extended periods, you’ll want to factor in that increased temperature as well.

The goal is to consider the additional heat sources outside the HVAC system itself. This should also include heat-generating appliances like your stove, refrigerator, and freezer.

Evaluating Your Home

Finally, your home itself has variables that will affect what you need. Your home’s construction is actually critical for evaluating those needs. Construction variables include:

  • Size, quantity, and type of windows
  • Amount and type of insulation
  • Ceiling heights
  • Ductwork type and insulation

Additionally, exterior factors may influence your size. For instance, whether your home is mainly shaded or in full sun all day will change your needs based on radiant warming. Your landscaping may also alter the temperature, especially if you have a lot of concrete or stone around your home instead of green vegetation.

Residents and businesses around Roseville have turned to [comapny_name] for expert heating and cooling solutions since 1948. Our multi-certified team offer heating and air conditioning installation, maintenance, and repair in addition to indoor air quality and water heater services. Call to schedule your consultation with one of our expert HVAC installers today.

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