Summer in Tennessee can be brutal.

With an average high of near 90 degrees in July and August and the occasional 100 degree days, most homeowners don’t want their air conditioners working overtime when the high temps hit.

You also don’t want to buy more AC for your home than needed.

One of the downsides of having an oversized unit is that they cool the air too quickly. That means it will cycle on and off too often, which will shorten the life of the unit.

Air conditioners operate most efficiently when they run for a long period.

If the unit doesn’t run long enough, it won’t extract enough moisture from the air.

As Tennesseans know, the more humid the air, the damper it feels. And if the air is humid and cold, it will feel clammy.

So what size HVAC unit does a building or home need?

It depends on the building, residential and commercial buildings have different needs.

Knowing the size of your HVAC unit isn’t just the physical dimension. It’s the BTUs.

A BTU is a British Thermal Unit, which is the traditional measurement used in the United States.

A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

For residential buildings, multiply the square footage of the area that needs to be cooled by 25 BTUs to calculate the cooling needs of your home.

So for a 1,000-square-foot house needs 25,000 BTUs.

But HVAC units are sold by the ton?

One ton can remove 12,000 BTUs in an hour.  So your 1,000-square-foot house needs a 2-ton unit. (1,000 X 25 = 25,000/12,000 = 2.5 tons)

This simple formula creates a pleasant environment inside, no matter the summer heat outside.

Business owners, on the other hand, have a harder task in front of them to ensure their AC unit is the correct size to help control their overhead costs.

Commercial buildings generally have higher ceilings, more traffic and different insulation from residential units.

The formula is to divide the square footage by 500 then multiply this number by 12,000 BTUs.

Now you need to account for all the sources of heat, like windows, doors and people. Add 380 BTUs per person and 1,000 per sun-face window and door. If there is a kitchen, add another 1,200 BTUs.

This will give you a good estimate of how large a unit you need to meet your needs.

By choosing the appropriate cooling capacity, whether it is for a whole house or even a window unit, you will get the best efficiency and lower your operating costs.

When should you replace your HVAC unit?

As temperatures rise in Tennessee during the spring and summer months, you may notice your HVAC unit working extra hard to keep up with a comfortable inside temperature.

While there are many things you can do to make sure everything is working as efficiently as possible, the cold truth may be that it’s time to repair or replace your HVAC unit.

If you’ve replaced the air filter, cleaned the unit and cleared away any debris, unclogged the pipe near the unit and made sure the thermostat is working accurately, you’ve done most of what we recommend.

The following items are signs that it may be time to call a professional.

Your HVAC unit is getting old

When did you buy your HVAC unit?

The average unit can last 15 to 20 years. But depending on how much it’s been used and how well it’s been taken care of, you may need a new one sooner.

Scheduling regular maintenance and frequently changing the filter can extend the life of your unit.

But if it’s older than 10 years and isn’t working as well as it once did, it’s time for an inspection.

You detect unusual sounds and smells

Obviously, you can hear your HVAC unit when it kicks on and while it’s pumping air into your home.

But that should be a relatively quiet sound. If you’re hearing clangs and bangs, something is wrong. This could mean you need a part – or the entire unit – replaced.

If a musty smell accompanies your HVAC unit turning on, this could be a sign there is mildew or mold that should be addressed.

If you smell gas, it could be even more serious. We recommend you leaving the house and calling a heating and air professional immediately.

Low SEER rating

Your unit’s Seasonal Energy Efficiency Ratio rating measures the ratio of cooling output over a season divided by the energy it consumed.

Essentially, it lets you know how efficient your unit is going to be, and therefore how much it will cost you to operate it.

Most air conditioners these days have a SEER rating between 14 (good) to 25 (great).

The higher the number, the more you’re likely to spend on the front in and save in the long run.

As standards improve, newer units are most often going to be more efficient than older ones. If your unit has a low SEER rating, it may be time to upgrade.

Your HVAC unit is too small

When most people buy their homes, they don’t immediately update the HVAC unit.

But over time, they may realize the unit in their home doesn’t suit them.

Some people simply like to be cooler in the summer and warmer in the winter.

If you’re one of these people and your HVAC unit can’t keep up with your desired temperature, you should consider getting a larger unit.

Costly repairs

Whether it’s a car, a kitchen appliance or an HVAC unit, there comes a time when fixing something can eventually cost more than just buying a new one.

We always urge customers to consider our maintenance plan so that we can stay on top of any issues you might have.

If it’s been a while since we’ve seen you and problems have piled up, you may be looking at frequent breakdowns and costly repairs.

In this case, the best course of action may be to buy something new.

What Does a New HVAC system cost?

A new HVAC system could cost more than $10,000 if you replace the central air conditioner, furnace, and ductwork.

But you could save substantially by following a few simple tips.

Estimating the HVAC system cost

Estimating the cost is difficult because of many factors. How large is your home? What is the quality of the equipment? How energy efficient do you want it to be? Is the furnace gas or electric?

These are a few questions that need to be answered beforehand.

And this doesn’t even account for the labor cost of installing the system. If your home is a challenge, there is a chance it will cost more.

In general, a heating, ventilation, and air conditioning system has a few basic component parts: the furnace, which supplies the heat; the air conditioner, which cools the air; the ductwork, which delivers the conditioned air throughout the home; and the thermostat, which is responsible for running the unit.

A straightforward installation for a full unit in a 1,000-square-foot home runs an average of $6,000 to $12,000.

For just central air conditioning expect the cost to range from $3,000 to $5,000.

A new furnace costs between $2,500 and $7,500. Ductwork could run from $1,000 and more.

How to control costs

1. Get an energy audit.

Before you start, you should get a reinstallation evaluation and energy audit. It adds costs at the beginning but can save you in the long run. You can do a small self-audit thanks to TVA.

By having a professional evaluate your home, you can save by installing the exact unit that meets the needs of your home.

It can also identify air leaks, like in the ductwork, and issues that impact the efficiency of your home.

2. Find the perfect contractor.

You might be tempted to go with the lowest bid, but remember you get what you pay for.

According to the EPA, nearly half of all HVAC systems are installed incorrectly. Those flaws can add up to a 30% reduction in efficiency.

Ask your friends for referrals and read online reviews before you decide on three companies to call for estimates.

3. Schedule in the off-season.

HVAC contractors are busiest when temperatures are at the extremes.

So schedule the replacement for spring or fall and avoid summer and winter. This can reduce labor costs because workers aren’t balancing a heavy workload.