How To Determine What Size HVAC Unit To Buy in Loveland, CO


When purchasing a new HVAC system for your home in Loveland, it’s important to determine the right size unit to avoid problems with indoor air quality and energy efficiency. 

Oversized cooling systems can be noisy and increase the chances of mold growth while costing too much. In contrast, an undersized system may struggle to maintain your desired temperature, leading to excessive wear and tear.

As a trusted HVAC contractor, we strongly recommend having a Manual J calculation done for your house to determine the appropriate size for your HVAC unit. 

The Manual J calculation is a detailed process that considers all the relevant factors specific to your home to provide accurate information that allows us to recommend the perfect HVAC unit size.

While rules of thumb (like one ton of cooling per 400-500 sq ft of building area) can be helpful, they don’t account for important factors like insulation, local climate, and other unique aspects of your home.

To ensure that your HVAC system is appropriately sized for your home’s specific needs, Loveland HVAC contractors rely on the recommended sizing procedures outlined in Manuals J and S, produced by the Air Conditioning Contractor’s Association of America (ACCA).

This guide will show you how to determine the right HVAC system for your heating and cooling needs. 

Read on.

How to Determine the HVAC System Size Needed

The general steps to HVAC system selection are:

  • Calculating accurate heating and cooling loads.
  • Selecting cooling equipment.
  • Selecting heating equipment.
  • Designing the ducts.

The first step in selecting the right HVAC system size is to determine the accurate heating and cooling loads using the ACCA Manual J procedure. Your local HVAC contractor will perform a load calculation that considers several factors specific to your home, including square footage, ductwork, climate zone, number and style of windows, quality and amount of insulation, natural shade or sunlight, number of people using the space, and heat-generating appliances. 

After determining the load calculation, you’ll have an accurate estimate of the number of British Thermal Units (BTUs) per hour of heating and cooling you need for your home.

For reference, one ton of air conditioning removes 12,000 BTU/h.

Next, select the cooling and heating equipment based on Manual S, which will ensure that the equipment is appropriately sized for your home’s specific needs. The sizing calculations should also consider any efficiency measures incorporated in the home, which can reduce the recommended size of the HVAC system.

It’s important to note that the design of the HVAC system will be an iterative process. Once we’ve completed the duct system configuration and preliminary design, we may need different equipment to achieve the proper airflow to satisfy each room’s heating and cooling loads.

When determining the correct size of your HVAC system, we use precise area measurements and other specific data. Exaggerating temperatures for indoor heating and cooling set points can significantly impact required equipment size, so we judge based on your comfort preferences before altering recommendations.

A programmable thermostat can help you condition your home before you arrive and avoid the temptation to over-size equipment for rapid cool-downs or warm-ups. Additionally, selecting variable-speed air handlers can improve energy efficiency and comfort in hot-humid and hot-dry climates.

Finally, your ducts play a critical role. Air leakage and heat losses from ducts can reduce your conditioning system’s capacity under peak conditions, resulting in reduced efficiency and comfort. Ensure your ducts are properly insulated and sealed to avoid potential issues.

How to Choose the Correct HVAC Size

Choosing the correct HVAC system size requires performing documented sizing calculations using the Manual J procedure and considering all relevant factors like design temperatures and insect screening. 

Your Loveland HVAC contractor should use the most up-to-date procedures when performing the Manual J calculation to ensure your HVAC system is appropriately sized for your home’s specific needs. The latest version of Manual J incorporates large impacts on efficiency, like duct leakage and duct heat gains and losses, which can significantly affect the HVAC system’s performance.

The recommended design temperatures for your location should also be considered when choosing the right size for your HVAC system. Using the annual extreme temperatures can lead to oversizing, so stick with the suggested design temperature after the Manual J calculation.

If you have insect screening, we will also consider that when sizing your system.

How To Determine Which HVAC System To Buy

When selecting an HVAC system to buy, it’s best to work with an experienced HVAC contractor who can give you detailed information on the available heating and cooling products. If your BTU size requirement falls between two sizes, we recommend choosing the closest larger unit.

For example, if the Manual J calculation recommends 18,000 BTU/h for heating, but the HVAC manufacturer only has furnaces that handle 17,000 BTU/h or 22,000  BTU/h, it’s best to choose the 22,000 BTU unit to ensure the system can meet peak load. 

While the 22,000 BTU/h unit is oversized, choosing the smaller unit would result in inadequate cooling, discomfort, and potential problems like mold and poor indoor air quality

A qualified HVAC contract near you can assist you in selecting the right unit size that fits your needs based on factors like your home’s size, climate zone, and insulation, as well as your budget.

Final Thoughts: How Big HVAC Do I Need

Choosing the right size HVAC unit is crucial for optimal indoor air quality, energy efficiency, and comfort in your home. 

When purchasing an HVAC system, rely on precise sizing calculations rather than general rules of thumb. The Manual J calculation considers factors such as square footage, insulation, climate, windows, and more to estimate heating and cooling loads accurately. This ensures you select the right-sized unit tailored to your home’s needs.

Call or message our HVAC specialists in Loveland, CO, to schedule a consultation and perform a Manual J calculation for your home. Our experienced team will guide you in selecting the perfect HVAC unit size, ensuring optimal comfort, energy efficiency, and indoor air quality for your living space.


How do I determine what size HVAC unit to buy?

The most accurate way to determine the correct size of an HVAC unit is to have a Manual J calculation performed for your home. One commonly accepted estimate is that an HVAC unit should provide one ton (12,000 BTU/h) of cooling for each 400-500 square feet of building area. However, this rule of thumb does not account for the local climate or how well a house is sealed and insulated.

Is it better to undersize or oversize HVAC?

Select HVAC equipment large enough to meet the heating and cooling loads during peak periods but small enough to maintain energy efficiency. 

An undersized unit may struggle to reach and maintain a comfortable temperature, especially on the hottest days when the cooling load is at its peak. The system will run continuously but may not have enough capacity to adequately cool the space, resulting in discomfort and potentially high energy consumption.

Conversely, an oversized unit may cool the space quickly but not run long enough to effectively remove humidity. This can lead to high indoor humidity levels, which can cause discomfort, promote mold growth, and compromise indoor air quality.

Work with a qualified HVAC professional who can accurately assess your home’s heating and cooling needs and recommend the best system size. 

What happens if my HVAC is too big for my house?

Oversized cooling systems can indeed have several negative consequences. Firstly, they can be noisy due to the larger capacity and increased airflow. This can lead to discomfort and annoyance for occupants in the home. 

Secondly, oversized systems often fail to provide adequate thermal comfort. They tend to cycle on and off more frequently, which can result in inconsistent temperatures and discomfort.

Moreover, excessive moisture removal is an important function of air conditioning systems. However, oversized systems run for shorter durations, leading to insufficient dehumidification.

What is the rule of thumb for HVAC sizing?

A commonly used rule of thumb for HVAC sizing is to provide one ton (12,000 BTU) of cooling for every 400-500 square feet of building area. But this rule of thumb does not work for most homes because it doesn’t account for insulation, local climate, and other specific characteristics of your home. We recommend having a Manual J calculation performed by an HVAC professional to ensure proper sizing.