Why Does My HVAC System Need to be Sized for My Henderson Home?

an HVAC system that has been sized for a Henderson home

The HVAC system in your Henderson, Nevada home should be properly sized. Too small and it won’t keep you comfortable; too large and it won’t be efficient. A professional HVAC contractor can calculate your home’s unique heating and cooling needs and recommend correctly sized equipment.

Problems with an Undersized System

If your air conditioner or heating system is too small, it won’t be able to keep your home comfortable when you need it most. You’re at risk of freezing on the coldest days of the year, and sweltering on the hottest. Because it’s important to keep your family comfortable all year round — no matter what the weather — you need to make sure your home’s HVAC system isn’t undersized.

Be aware that if you’ve added another floor to your house, built an addition, or enlarged your living space, you may need to have a professional assess your home’s heating and cooling needs. Any major renovations that change the shape and size of your living space will affect your HVAC system’s operation. Have a contractor size your HVAC system to make sure your current unit can keep your home comfortable.

Problems with an Oversized System

Installing a larger-than-necessary heating or cooling unit might seem like a good idea. Logically, it should be powerful enough to keep you comfortable even in extreme temperatures. The problem is that an oversized system ends up costing you more money than a properly-sized system, and it can actually make your home more uncomfortable, not less.

An oversized heating or cooling system tends to short-cycle, which means it starts up and reaches temperature quickly, then shuts off. The unit will have difficulty keeping your home at a constant, comfortable temperature. A short-cycling system also circulates air through your home inconsistently, creating cold or hot spots.

Since an oversized system doesn’t operate steadily (the way it’s supposed to) it never achieves peak efficiency. Even if a unit is rated for high efficiency, if it’s oversized you’ll pay more than necessary on your energy bills.

The larger your HVAC system, the larger the initial cost. Buying an oversized furnace, air conditioner, or heat pump is a waste of money. Choose a correctly-sized system and you’ll pay for exactly what your home needs, not more.

How to Size Your Home’s HVAC System

There are several methods a contractor uses to determine the correct size furnace, air conditioner, or heat pump for your home. To correctly size your HVAC equipment, a contractor should use the Air Conditioner Contractors of America (ACCA) Manual J calculations.

The most basic way to estimate heating and cooling needs is by using square footage. This method is easy to use, but it doesn’t take into account specifics of your home like climate information, insulation, drafts, or added heat from the sun. You’re likely to get an oversized HVAC unit using square footage to estimate heating and cooling needs.

If you’re replacing an existing heating or cooling system in your home, it may be tempting to simply replace it with an identical unit. The problem with using your current unit to size your new one is that, unless your current unit is the proper size, you’ll end up with either an oversized or undersized unit. Especially if you’ve completed some energy efficiency upgrades in your home, you need to have a contractor size your HVAC system.

The most accurate method for determining the correct size HVAC unit for your home is using ACCA’s Manual J. Contractors typically use software to complete the complex Manual J calculations. These formulas take into account the unique properties of your home including insulation, how much sunlight hits your home, climate information, window types, the number of occupants, and how well-sealed your home is.

Understanding Heat Gain and Heat Loss

One of the reasons it’s important to use Manual J calculations (rather than square footage) to size your HVAC system is because Manual J takes into account heat gain and heat loss.

Heat constantly moves through your house — besides coming from your HVAC system, heat also comes from lights, appliances, and people. Heat can also move through solid surfaces like your walls and roof to add to your home’s heat gain. Heat loss is when the heat in your home escapes to the outside, such as through leaks and drafts.

Depending on the outdoor temperature, your home’s heat loss and heat gain will change throughout the year. In the warm weather your home gains heat, and in the cool weather it loses heat. To properly size an HVAC system, a contractor should measure the movement of heat throughout your house and account for the outdoor temperature.

Each room in your home is different, and will lose and gain heat differently. A contractor needs to determine the heat loss and gain in each room separately to get an accurate picture of your home’s heating and cooling needs. If your home has an open floor plan or multiple floors, it makes for complex calculations.

Understanding Efficiency Ratings

Whether you’re purchasing an HVAC unit for a new home, or replacing your current unit, it’s worthwhile to learn about efficiency ratings. There are three common efficiency ratings you should know about: AFUE, SEER, and HSPF.

  • AFUE: The efficiency of furnaces is rated by annual fuel utilization efficiency, or AFUE. The AFUE rating is a percentage of the amount of fuel used to produce heat. For example, a unit with an AFUE of 80 percent uses 80 percent of its fuel to produce heat, while the other 20 percent goes to waste. When you’re deciding on a heating system for your home, consider efficiency as well as heat output. For example, consider a unit with an AFUE of 85 and a unit with AFUE of 95, both with identical output. The unit with higher efficiency might actually be too big for your home.
  • SEER: An air conditioner’s efficiency is noted by its seasonal effective efficiency ratio, or SEER, which rates the unit’s cooling efficiency. The higher the SEER the more efficient the system. A SEER rating is calculated by comparing a unit’s cooling power to its electrical input, taking into account the changing outdoor temperature over a season. In the United States, new air conditioners have a minimum required SEER of 14. The most efficient units can have a SEER rating as high as 26.
  • HSPF: If you’re installing a heat pump — also called a packaged unit — in your home, you’ll have two efficiency ratings to consider because a heat pump provides both heating and cooling. The SEER rating that applies to air conditioners is also used to rate the cooling power of heat pumps, but the rating for heating efficiency for heat pumps is called the heating season performance factor (HSPF). The HSPF takes into account a unit’s electrical input and compares it to heating power, and accounts for temperature variation during the heating season.

Here in Nevada, the cooling season is longer than the heating season. Because you’ll be cooling your home longer than heating it, you should be particularly interested in a heat pump’s SEER rating. It could happen that you find a heat pump with an ideal cooling capacity that falls short on heating. In that case, you can consider installing supplemental heat to keep your home comfortable during the cool season.

Ensure your HVAC is efficient and properly sized, and you’ll enjoy a comfortable home and energy savings month after month. Have an HVAC contractor complete ACCA Manual J calculations for your home to avoid installing a costly oversized system, or an inadequate undersized system. At Ambient Edge we have over 10 years of experience installing HVAC units in the Henderson, Nevada, area. Call us at 702-479-7464 to have one of our professional technicians recommend an HVAC unit for your home.

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