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What's The Right Size of Air Conditioner for Your Home?

At Fire & Ice we use a Manual J Load Calculation to determine the exact size of the system that is best for your home.

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August 13th, 2020

What’s the right size of an air conditioner or heat pump for your home? What size furnace do I need? How do you determine which size is best for you? In this video we’ll discuss load calculations and why they’re important when it comes to choosing a new HVAC system.

Hi, I’m Luke with Fire & Ice. Over the years, we’ve met with thousands of Central Ohio homeowners to help solve their HVAC needs. Sometimes during a sales estimate we're asked, “Why can’t we use the same size of my current system?” or “Why do you need to measure my windows and doors? I thought you were here for my air conditioner.”

The simplest answer is we take the extra step to find the best solution for our customers. To do this we perform what’s called a Manual J Load calculation and we do this on every one of our estimates. In this video we’ll discuss what a manual J load calculation is, why it’s needed, and how it’s used to find the right size of equipment for your home.

What is a manual j load calculation?

A manual J load calculation that calculates the amount of heat your home gains and loses per hour naturally in a given season.  The calculation determines what size HVAC equipment is needed when heating or cooling a home. Both the Air Conditioning Contractors of America and the US Department of Energy recommend a manual J load calculation be performed for every HVAC job.

Why do you need a calculation?

Now you may be asking, why is it important? My current system was working fine, why not use the same size? The problem is we don't know if your previous system was even sized correctly. In fact, we've found many homes don't have the right size HVAC system installed after we perform a load calculation during sales estimates. Improper sizing can lead to many problems such as: insufficient heating or cooling, negative performance of your HVAC equipment, premature breakdowns, and wasted energy. A manual J load calculation is the best way to determine the proper size HVAC equipment that will meet the needs of your home.

What’s the process?

A manual J Load calculation produces two numbers: the total amount of BTU’s per hour gained and the number of BTU’s of heat loss per hour. BTU’s stands for British Thermal Units and is a unit of measure for heat. It's the amount of heat needed to raise the temperature of one pound of water one degree Fahrenheit. And that ends today’s science lesson. I promise we won’t get any more technical than that.

Both heating and cooling calculations in a Manual J factor in the square footage of all exterior windows, doors, walls, ceiling height and more. The cooling component looks into how much heat comes into the home and is retained per hour while the heating side looks at how much heat is lost in an hour.

On the cooling side, one of the most important factors are the number of windows and their orientation to the sun. A lot of heat can come into the home through the windows when they're in the direct path of the sun. Homes with many windows facing east or west can be considerably warmer than a similar style home facing a different way.

For the heating side the type of glass and construction of the windows and doors are considered, as well as how many panes of glass your windows have.

Other factors include the presence of a basement or crawl space, the amount of insulation in the walls and ceiling, number of stories, the number of inhabitants in the home, and more.

What does the calculation mean?

Now that the calculation is complete, what do we do with those numbers? At that point we can determine what size equipment is needed. For cooling, we know for every 12,000 BTU's of heat gain per hour 1 ton of air conditioning is needed. For heating, the number of BTUs of heat loss will determine the amount of BTU’s a furnace will need to supply to sufficiently heat your home.

What are the ranges in size for your home?

Now that we know how many BTU’s of heat gained or lost in the home naturally, it's time to put it all together. When it comes to cooling your home, every 12,000 BTUs of heat gained requires 1 ton of air conditioning. In the HVAC industry cooling equipment range in size ranging from 1.5 ton up to 5. Sizes for most models go up in half-ton increments up to 4 and then from 4 to 5.

On the heating side, furnaces are sized based on the amount of BTU’s they can supply per hour. Typical residential gas furnaces range between 44,000 BTU per hour to up to 120,000 BTU’s.

The efficiency of a furnace plays a part as well. A standard efficiency furnace will need a higher output compared to a high efficiency furnace due to less efficiency. A home of 55,000 BTU heat loss will need a 60,000 BTU high efficiency furnace but an 80,000 BTU standard efficiency unit due to the loss of efficiency.

What are the next steps?

Now that you know what’s required in order to get the right size HVAC equipment for your home, be sure to ask your HVAC professional if a manual J load calculation will be performed at your next estimate. If you’re in the Columbus, Ohio area and are looking to invest in a new HVAC system click the schedule estimate button at the top of the screen to schedule a free estimate. We’d love to help solve your HVAC needs and find the best solution for your home. Thank you for watching and we look forward to making your day better.

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