Buying a gas furnace in 2017 can be complex without an understanding of what’s available. That’s the purpose of our 2017 furnace buyers guide – to assist you in choosing a gas furnace that hits the right targets for you whether budget, indoor climate control and/or ecofriendly efficiency.
You might also be interested in our:
- Top Rated Gas Furnaces 2017 Guide looks at the best-quality, most reliable furnaces with examples from all the efficiency classes
- Most Efficient Gas Furnaces 2017 Guide that covers just that – furnaces that use the least amount of energy to heat your home
Gas Furnace Efficiency Options
Here are your gas furnace efficiency choices and tips for deciding which is right for you.
One more note (we know, get on with it, right?):
- AFUE is Annualized Fuel Utilization Efficiency. It’s like gas mileage for furnaces – how much heat the furnace creates per the gas consumed. Furnaces are listed in terms of AFUE in this form: 95% AFUE. That means the unit makes use of 95% of the gas burned. The other 5% is lost along with the combustion gases. We’re going to drop the use of AFUE in this guide.
80% Efficient Gas Furnaces
A full 20% of the heat created goes up the chimney, and many find that very annoying. Every brand makes 80% efficient models, usually in their base and better series. The main reason for this efficiency level is that these furnaces have a single heat exchanger and are cheap to make. Reasons to consider an 80% furnace include:
- Winters are mild-to-warm where you live and heating bills are low, so spending $1,000 more to save $5-$10 per month on heating isn’t cost-effective.
- You’ll sell your home soon, so you won’t get your money out of an efficient gas furnace (though in cold climates, an 80% furnace might deter some buyers)
- The furnace will be used part time as in a guest apartment, vacation home or workshop not heavily used
90%-95% Gas Furnaces
These furnaces achieve impressive efficiencies with the use of a secondary heat exchanger that draws additional heat from combustion gases before they are exhausted. Most are Energy Star rated, and the installation of one might qualify for credits and rebates from your energy company. Find out here. Consumers that choose a 90% to 95% furnace often list one or more of these reasons relative to an 80% furnace:
- Lower energy costs and possible rebates, a financial decision
- They’re staying put long-term, so will recoup the higher purchase cost
- An efficient furnace is a selling point when not staying in the home long-term
- Lower energy use, an environmental decision
95%-plus Gas Furnaces
All the leading furnace brands make furnaces in this range with the most efficient being the Heil QuietComfort Deluxe 98, Lennox SLP98V and Carrier Infinity 98 Greenspeed, all at least 98% efficient. They achieve superior efficiency with a variable-capacity gas valve (see the Performance section) secondary heat exchanger and condensing technology that draws additional heat out of the moisture created as a byproduct of combustion. Top-efficiency furnaces qualify for rebates and credits too.
The common reasons given for buying a 95%-plus gas furnace are the same as for buying a 90% to 95% furnaces. These furnaces are costlier, but the energy use and cost savings are more substantial too.
Gas Furnace Performance Options
How comfortable do you want your heat to be in terms of balance, humidity and noise? Here are your three basic choices for performance, and they have an impact on efficiency too.
The gas valve on these furnaces open fully, and the burner fires at 100% capacity. The one advantage is that single-stage furnaces are inexpensive compared with furnaces of the same efficiency and better performance. Most single-stage furnaces are 80% models, but as technology has increased, efficiency have risen. The Trane XT95 (95%), American Standard Silver 95 (95%), Bryant 925S (96%) are Energy Star rated, cost-cutting furnaces.
The disadvantages of single-stage heating include:
- A burner at full capacity is loud
- By the time the thermostat registers adequate heating, the full-capacity burner has created excess heat that could boost your home’s temperature by a degree or two beyond what you want it to be
The gas valves/burners in these furnaces have two capacities. They burn at 65% capacity (and noise) most of the time, only kicking to high when outside temperatures drop quickly or you turn up the thermostat. While the two-stage heat technology boosts furnace purchase cost by 15% to 25% depending on the model, the advantages are:
- Quieter heating
- Better temperature balance
- Less wasted heat
- Better humidity control than single-stage furnaces
Instead of one or two capacities, the gas valves in these furnaces modulate in increments of 1% or less to produce the precise amount of heat required to keep your home comfortable. The terms modulating and variable-speed are also used for variable-capacity. A few furnaces can run as low as 25%, though most start at about 40% capacity. The downside to these furnaces is their cost – 20% to 35% more than two-stage models, but the cost difference is coming down as their popularity grows and more are being produced. Advantages of variable-capacity heating are:
- The quietest heating
- The best temperature balance
- The least wasted heat
- The best humidity control in summer, and in winter too when equipped with a humidifier
Gas Furnace Capacity
Furnaces start at about 40,000 BTU/hour and can be as large as 155,000 BTU per hour. It’s important that your furnace be just the right size for your home. The disadvantage of a furnace with too little capacity is obvious, but a furnace that is too large will be inefficient because it creates more heat than necessary, and when furnaces come on for short cycles, that can harm them mechanically.
Ask your HVAC company to test to determine the proper size furnace for your home. The testing is typically called a Manual J load calculation. An enormous number of factors are included – your climate, several aspects of your home’s construction, foundation type, roofing material, level of insulation in walls and the ceiling, number and type of windows and doors and other factors. Your home’s air-tightness might also be tested. A load calculation is the only way to accurately size a gas furnace. If any of the factors mentioned have been upgraded – new and better windows or an additional layer of insulation in the attic, for example – then your new furnace should be smaller than the one it replaces.
Now, let’s say it is determined that your home needs a furnace with 100,000 BTU capacity. That number is the BTUs that make it into your home, not that are created. Furnaces have Input (BTUs created) and Output (BTU efficiency ratings). Here are sample furnace sizes you would need at various efficiency levels. Since most furnace models are made in increments of 10,000 to 20,000 BTUs, the size won’t be “perfect.”
- 130,000 BTU input x 80% efficiency = 104,000 BTU output
- 110,000 BTU input x 90% efficiency = 99,000 BTU output
- 105,000 BTU input x 95% efficiency = 99,750 BTU output
- 105,000 BTU input x 97% efficiency = 101,850 BTU output
- 100,000 BTU input x 98% efficiency = 98,000 BTU output
It’s the output that matters. That list shows just how wasteful some furnaces are.
Gas Furnace Buying Tips
Let’s summarize the information in our gas furnace buying guide with a few tips:
- The colder your winters are, the more it makes sense to buy an efficient furnace
- The longer you intend to live where you are, the more you will save with an efficient furnace
- If you’re committed to green heating, then buying the most efficient furnace you can afford (cool-to-cold climates) or choosing a heat pump instead (hot-to-cool climates) or a dual fuel system * with a heat pump and a furnace (cold-to-very cold climates) will give you peace of mind by significantly reducing energy use
- If indoor comfort control isn’t a high priority, then you can save money with a single-stage furnace at the right efficiency level for your climate
- If climate control is important to you, then choose a two-stage 80% furnace (warm climate) or 90%-95% furnace (cool climate) or a variable capacity furnace (cold climate) for the most cost-effective comfort
*A duel fuel system employs a heat pump to do the heating in temperatures above freezing and a gas furnace for temperatures below freezing when a heat pump becomes ineffective/inefficient
Have Your Furnace Installed Properly
Bad installation will rob your gas furnace of efficiency, dependability and ultimately of durability. We doubt you plan to hire “some guy your buddy knows who does it on the side,” but even among HVAC pros, it pays to hire a qualified contractor with certification and experience. Get multiple estimates by making calls and following up on them to learn about each potential installer. Another option is to use our Free Estimates tab to get several written estimates from some of the top HVAC technicians in your area. They are prescreened for experience and to make sure they’re licensed and insured, and they know they are competing for the work. There is no cost or obligation to you, and one simple form gets the estimates rolling.
Has this 2017 gas furnace buying guide assisted you in sorting out the issues to consider? If so, perhaps your friends and followers on social media would appreciate you passing it along to them.