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Things to Consider When Buying A New Furnace

podcast, audioHeating equipment is one of a homeowner’s major expenses.  The efficiency of your furnace can make a big difference in your energy bills. A new furnace will save money on your heating bills, be safer, and greener (better for the environment).  Our best advice is to plan ahead!  Don’t wait until the dead of winter and your heat has gone out to start thinking about replacements. In fact, you’re likely to get the best pricing on a furnace in the spring or fall.

Average Lifespan of a Furnace is 15 Years

aging HVACDon’t know how old your furnace or heat pump is?  Open the cabinet and look for dates.  Write down the model number and search the Internet to find an approximate date of manufacture. If your furnace has a standing pilot light instead of electronic ignition, or its AFUE (Annualized Fuel Utilization Efficiency) rating is less than 80%, this is a sign that it is obsolete and wasting energy. If your heat pump has a HSPF (Heating Season Performance Factor) of less than 7.7, you should consider replacement. If you already know your existing furnace won’t make it through another winter, or you’re facing major repair bills on a furnace at least 15 years old, you should buy a new one now.

Types of Systems

split system, HVAC furnaceGenerally, you’d want a central heating solution, unless you are forced into a local heating solution due to not having any ductwork.  For a local solution, a mini-split system is ideal because it does not require ductwork and is extremely efficient (see our previous posts on mini-splits here: 1, 2, 3).  For central heating, you can go with a split or packaged system.  Split systems are most common, and have a condensing unit and coil that sits on top of your furnace.  They have an indoor component and an outdoor component, hence the term “split.”  Packaged units mean it’s all in one unit and that unit can sit outside.

What Fuel Type Is Best?

gas furnaceNatural gas is the least expensive way to heat. Oil or propane furnaces are an option only if your home does not have gas lines.  Electric furnaces (heat pumps) are more efficient than natural gas, but producing heat from electricity is more expensive. A heat pump can also act as an air-conditioner in the summer, so can be used year-round.  If you have a natural gas furnace, you’ll still need another option for air-conditioning. Some systems are dual-fuel systems, which use a heat pump (electricity) to heat and cool your home, and a gas furnace which serves as the back-up heat source and helps deliver the heated air produced by the heat pump.

Size: How Large a System Should You Buy?

Don’t just blindly get the same size that was originally in the house, as additional space may have been added over the years. In order to size a system appropriately, a load calculation must be done, taking into consideration the square footage of the home, ceiling height, shade around the home, insulation, types of building materials, and the numbers and types of windows and doors. If you get a system that is too big or too small, it won’t work well (it won’t provide good temperature and humidity control), will not be efficient (you won’t see the fuel cost savings you’d expect from a new system), and will break down sooner.

Efficiency is the Key

AFUE, Energy Guide, EfficiencyAlways go with the most efficient furnace you can afford, the one with the highest AFUE number (Annual Fuel Utilization Efficiency rating).  This is the number on the yellow “Energy Guide” label on the unit.  Just remember, the higher the AFUE, the lower your monthly heating costs.  Energy Star, efficiency

Look for the ENERGY STAR® label and certification on the unit to be assured it will meet government efficiency standards. Other criteria to look for include:

  • A variable speed blower motor.  This will save energy and reduce noise.  A fixed-speed blower blows hot air into the house full force for a few minutes, then shuts off – often resulting in pockets of warmer and cooler areas.  A variable speed blower blows faster when it’s colder outside, and then slower for longer periods, providing quieter and more even, comfortable heat.
  • A sealed combustion chamber: this not only makes the system quieter and more efficient, but safer, too, as it avoids the possibility of introducing combustion gases into your home.
  • A second heat exchanger with condensing flue gases and/or 2-stage gas valves.

Installation: What to Expect

Installation takes about a day, but can take several days if your ductwork also needs to be replaced. Never compromise on installation quality.  A poor installation may mean the unit won’t perform at its potential and could cost you more to run. Be sure your new system is installed by a certified licensed HVAC contractor with a proven track record of successfully installing similar systems to yours.

A Good Time to Consider Options

ThermostatAny time you’re considering a major replacement, may also be a good time to consider other options.  For example, installing a multi-zone system will allow you to control multiple areas of your home independently with separate thermostats without buying separate systems. Getting an electronic programmable thermostat will give you more precise control of temperature and could lower your energy bills by up to 30%.

Should you replace your heating and cooling systems at the same time?

In general, the answer is yes.  This is because mismatched systems may not deliver the energy efficiency or performance you expect, and could contribute to service problems later on. A central system uses the same ductwork for both heating and cooling so you want to be sure all parts work together.

Is Maintenance Necessary on a Brand New System?

furnace maintenanceYes. But only if you want it to last a long time, not have unexpected breakdowns, maintain its efficiency and perform at peak levels.  Check out our Fall Maintenance Guide (download here) and get a yearly service contract.  That way, you’ll know if there has been a recall or if a part is covered by warranty when it goes go out. Some warranties can be invalidated if you cannot prove the unit has been under a service contract.


Do not make a decision based on upfront pricing alone.  Check to see if there are manufacturer’s rebates or incentives you can take advantage of, or low interest financing, or tax credits.  Having a reputable HVAC contractor is more important than the price.  You’ll want to feel confident the system will be sized appropriately, installed correctly, and that the company will be around to offer on-going maintenance and support. A longer warranty should also be factored in, as it can translate into cost savings in the long run.

Selecting a Contractor

HVAC contractorYou should get multiple bids from reputable, licensed, NATE-certified HVAC installers. Make sure they inspect your home and be wary if they give you an estimate over the phone.  Get the estimate in writing and understand what’s included.  Ask about warranties and service agreements. Remember the best value may not come from the contractor with the lowest price. 

Now’s the time to focus on energy improvements in your home! If you live in the Nashville or surround area, give us a call at: 615-832-8500. Interstate AC Service will help you with all your heating and cooling needs.

Important Tips & Advice



You often don't think about your heating or air-conditioning system until something goes wrong. But there is so much you can do to help keep your system from breaking down. We regularly post information to help you learn what you can do to keep your system running, to save money and energy.  Search our many posts, videos, and podcasts, for valuable information that is never a sales pitch. Subscribe to receive an email when something new is posted, so you won’t miss any important tips.

Choosing a Repair Company

Whether you’re talking about heating or cooling, repairing or replacing a system, you want a company that can advise you reliably based on what is in your best interest, not based on what is convenient or what earns them the most money (commissions). We'll help you choose the best solution to fit your needs. Check out our many posts at HVAC News You Can Use and our podcasts.

Going Green

We're concerned about the environment and know all the latest technologies - such as geothermal systems, LED lights, and smart thermostats - that can reduce energy and put more "green" in your pocket!  We've provided HVAC systems in certified LEED buildings and written many posts on ways to Go Green.

The Sign of Service

We are a repair company performing a full range of commercial and residential heating, air conditioning, energy management and comfort products service, maintenance, and installation. We are a locally-owned company serving Nashville-Davidson County and the surrounding counties including Williamson, Rutherford, Wilson, Sumner, Robertson, and Cheatham.

Who We Are

Our service technicians are fully trained and experienced.  We can tackle the most complicated system to the simplest of systems – from large commercial plants to single-family homes.  Our ownership group of Eddie Hutton, Tony Anderson, Roger Eldridge,  Swaney Powers and Alan Seilbeck have over 125 years combined experience as leaders in the HVAC industry.


We are proud of our dispatchers that respond to your telephone call. When your system is down they make things happen. Our trucks are loaded with most parts needed for a quick repair. You can call day and night 7 days a week. Our normal weekday hours are 7:00AM to 5:00PM. Click on the button below to schedule a service call online. Emails and forms can only be answered weekdays from 7-5.”  

615-832-8500 Online Service Call


Did you know you should service your HVAC on a regular schedule – just like you would your car?  We have specialized maintenance programs to ensure the clean, energy efficient and safe operation of your HVAC systems.  This helps minimize service interruptions/breakdowns and maximize your equipment's lifespan.  All maintenance contract customers are assigned a primary technician that will get to know your facility and equipment and will treat it like his own.  You’ll receive discounts on repairs or new installations, and get priority service when it is cold or hot outside and you need service promptly.  Plus, maintenance contract customers are never charged overtime rates for emergency services after-hours, weekends or holidays. We’ll teach you how to save on maintenance costs by showing you things you can do yourself and when you need a technician. Here are some good posts:  Repair vs. Replace, Things to Try Before Calling for Service, Springtime Tips that Pay Off.


Our team takes on HVAC projects for office, school, retail and industrial facilities. Check out these case studies:

Replacement of a 250-ton Cooling Tower

Ductless HVAC at Brentwood Middle School