Importance of right size HVAC systems

Importance of right size HVAC systems

There is no doubt that some people might think that the bigger the heating or cooling system, the more comfortable they and their family would feel. Eventually, bigger HVAC units are a lot more powerful, and are most likely to be capable of providing the best possible heating and cooling, are you also the one who thinks that way? Well, there are also some of the people who would buy systems that are very small according to the size of their homes, with the belief that they would be able to save them money on energy because of the smaller capacity and apparently lesser power would be used.

Well, thinking like that is also right, because if you are already enjoying getting higher energy bills, shortened HVAC system life, having to repair your system or buy a new one more often, also if you have a less comfortable home because of all these temperature or humidity issues.

As far as HVAC systems are concerned, always remember that bigger is not always better, also going small would not do you any sort of good either. In this whole world, the only right way to go is to have the proper and rightly sized HVAC system in order to reduce your utility bill, expand the life of your HVAC system, as well as to make everyone comfortable all the time. Basically, the right sizing must include the proper understanding of the thermal envelope and doing all advanced calculations. You can never accomplish the optimal right size system by simply applying the HVAC industry’s Manual.

The problem with oversized HVAC systems

Where the size is concerned for all the power that all these oversized HVAC systems acquire, they never cool or heat any given space according to the expectations that they should. This is only because of the reason that they heat and cool very quickly, so as a result, the compressor and often these ventilation fans shut off. This repeated on and off action is called “short cycling.”

A short cycling HVAC system is most likely to lead to poor air circulation, which in return would lead to some sort of musty, congested, and more humid air in your entire house. With the passing of time, all these short cycling results in contaminant buildup and even possibly mold growth in your house. In fact, in worst cases, your oversized unit causes all these problems, it would always use more energy if it compared to the runs longer to achieve its optimum on and off-cycle, and eventually, it shortens the life of your system.

Along with that, the larger HVAC systems might cost you more than the smaller ones. So, any oversized system is likely to cost you more to buy, be more expensive to repair, and need to be replaced as soon as possible.

The bottom line is an oversized HVAC system is bad news for you any way you look at it.

The problem with undersized HVAC systems

In case you think of installing an undersized HVAC system is as same as bringing a compact car to a monster truck arena. Your heating or cooling unit would be very small for your entire home. There are high chances that it would leave your home too warm or too cold if the system is not large enough.

Along with that, even if it can heat or cool your home properly, it will always have to work so much harder than it is usually designed to, and it will also take very long to heat your home when cold or cool your home when hot. Worse, working overtime, outside of your system’s ideal cycle length, can damage an undersized HVAC system and lead to avoidable repairs and replacement.

How to size an HVAC system for the home?

While you are looking to install a new HVAC system in your home, it is very important for you to make sure that it is sized correctly. In case it is very small, it might not be able to regulate the temperature of your entire home. On the other hand, any HVAC system that is oversized will never work as efficiently, and it may also wear out faster, and possibly it will develop dehumidification problems. The whole process which is concerned in deciding the right size air conditioner and furnace for your home is a very complex process, but it is also possible to do a general estimate on your own.

Approximate Calculations

To verify the approximate size of your HVAC system, you can use the following calculations:

  • First, determine square footage: you must find out the floor space in your home. You will have to be able to find the number that must be written down somewhere, but in some cases, you might have to measure it all by yourself. In order to measure a room on your own, you can use a tape measure in order to determine the length as well as the width. You will then have to multiply those measurements together for the square footage in that room. You will have to repeat this process for each room and hallway, then add them all together.
  • Secondly, you will have to determine the base BTU: The unit that is used to measure the energy used for heating and cooling is the British Thermal Unit or BTU. The estimated amount of energy used to cool a square foot of your home is approximately 25 BTUs, so multiply the number of square feet in your home by 25 to get the base BTU measurement.
  • Thirdly, account for high ceilings: In case your home’s ceiling is over 8 feet, you can multiply the base BTU amount by 1.25, or even by 25%.

For a 1500 square foot home with normal ceilings, the result would be about 37,500 BTUs. Once you have the base BTUs figured for your home’s size, you can then figure out the size of AC and heating units you need. For the air conditioner, divide the number by 12,000 to determine the tonnage required. For the furnace, divide the BTU by the unit’s efficiency as a decimal.

In the case of a 1500 sq. ft. home, the air conditioner would need to be 37,500 ÷ 12,000, which comes out to about 3 tons. For the furnace, an 80% efficiency unit would need a BTU output of about 37,500 × 0.8, which is about 47,000 BTU.

How to size commercial HVAC systems?

A commercial HVAC system would provide space heating and cooling. The entire system is found in larger spaces like companies, large factories, restaurants, etc. Commercial HVAC size is rated in tons, and the available sizes increase by increments of 1/2 tons. The typical commercial A/C for small buildings differs from 2 to 30 tons for all these big buildings. 

Here are some simple steps for the ways to calculate the commercial HVAC size that you will need:

  • Estimate the square footage for the area that you would like to cool down any building or room group. You must notice that the equation below is focused on 8-foot ceilings, so a wider ceiling area would need even a wider system. 
  • You must use a volume of 500 to divide the square footage. 
  • You can then multiply Step 2 and 12,000. 
  • For every person who is working in the building all day, attach 380 Btu. 
  • In case the number vary, do take an average.
  • Add 1,000 Btu for each window within the space.
  • Add 1200 Btu each for each kitchen
  • In the end, to establish the size of the HVAC system, divide the amount of Btu you need by 12,000

How to calculate HVAC system size?

You will have to find out how many BTUs are actually necessary. The BTU measurement basically describes the size of the entire unit or units in tons. A BTU, or British Thermal Unit, is the total amount of heat that is needed to heat 1 pound of water one degree Fahrenheit. Though BTUs are significant, most larger air conditioning units are rated in tons. Since 12,000 BTUs equal 1 ton, an air conditioning unit rated at 3 tons can produce 36,000 BTUs.

Step 1:

You will have to calculate the square footage of the area to be cooled. You will then figure out if the office space will be divided into zones that are cooled by separate air conditioning units. Remember to keep these measurements separate.

Step 2:

After that multiply the square footage obtained for each area by 25.

Step 3:

Then you will have to add 400 for each person who works in that particular area.

Step 4:

Lastly, for each window, add 1,000.

Step 5:

The number gained from steps 1 to 4 represents the minimum BTUs that the air conditioning unit should provide.

  • These calculations are for rooms with an 8-foot ceiling. However, higher ceilings require a greater number of BTUs.

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