Q&A: Know When to Upgrade Your Furnace

An HVAC expert talks about the signs of an inefficient or aging furnace.

Do you have an older furnace in your home? Do you know how energy efficient it is? It could be costing you more money over time than you'd spend on a new, high-efficiency furnace.

Laura Paprocki, MGE Residential Services Manager

Laura Paprocki, MGE Residential Services Manager

MGE Residential Services Manager Laura Paprocki is talking furnace efficiency—and when it's time to consider upgrading—with HVAC Design Engineer Keith Ouimette of Cardinal Heating and Air Conditioning.  

Laura: Are there any obvious indicators that you have a lower-efficiency furnace?
Keith: The biggest thing that lets you know if it's a mid-efficiency or high-efficiency furnace is whether it's vented into the chimney. That means it's a mid-efficiency furnace with an original efficiency rating of about 80%. A high-efficiency furnace—rated between 92% and 98%—is vented out to the side of the house through PVC pipes.
Laura: Why do you call 80% "mid-efficiency?" Isn't that really low? Do you still see older furnaces built to run at 65-70% efficiency?
Keith: It is low. "Mid-efficiency" is what the HVAC industry calls furnaces that are 78-83% efficient. Even though today, there's not really anything lower than 80%, it's a title that has stuck.

Laura: How can homeowners find out the exact efficiency of their furnace?
Keith: The only way to truly know is to have an HVAC technician perform a combustion analysis on your system.
Laura: Is that included in a typical yearly tune-up and cleaning of your furnace? Or should one ask specifically for this test?
Keith: We regularly include this testing in our process because it's the easiest way to see if there is a failure in the heat exchanger—the part of your furnace that actually heats the air. But even if that isn't an issue, a combustion analysis will give an exact reading of the furnace's efficiency. It's always good to confirm that the company doing your tune-up also will include this efficiency reading.

Laura: Are there any visible signs your furnace has safety or performance issues?
Keith: Safety issues are not always visible, so it's very important to have your furnace inspected by a trained professional. Performance issues are a little easier to notice. If your furnace is running longer or shorter than normal, if it's not able to maintain temperature—these are a few things that are noticeable if you are paying attention.

Laura: When does it make sense to stop replacing parts and buy a new furnace?
Keith: We have a general rule that if you have an older furnace and the cost of a repair is 25% or more compared to the cost of a new furnace, you should seriously consider replacing it.

Laura: What is the cost difference to operate a mid-efficiency furnace versus a new, high-efficiency furnace?
Keith: In going from an 80%-efficient furnace to one that's 95% efficient—which is what we typically install—the average cost savings on natural gas would be about $200 per year. So, it's a pretty significant value.

Laura: If a homeowner decides it's time to buy a new furnace, where does he or she start?
Keith: They can look at EnergyStar.gov to find out which models are the most efficient. But they should check with a local contractor to find out which furnaces are actually sold in this area. They can also look into Focus on Energy incentives available for homeowners who upgrade their heating systems to see if they qualify.

Laura: There are some standard types of furnaces people should be aware of though, right?
Keith: Yes. Generally, the models sold now are either two-stage or modulating furnaces. Two-stage furnaces have two different firing rates—50% or 100%. That percentage relates to how much heat is being released. With a modulating furnace, you have multiple firing rates between 20% and 100%. That allows for a more constant flow of heat and a greater level of comfort throughout your home.

Laura: Keith, I just have one final question—and it's something I get asked a lot on MGE's Home Energy Line. People looking to replace an older furnace often wonder if they need a new one with the same number of BTUs, especially if they've upgraded their insulation over time. What do you usually advise?
Keith: We often find that heating systems put in houses 20-plus years ago are oversized. The focus used to be mainly on the amount of heat a furnace could produce. By performing a block load calculation on the home, we often find that we can downsize the furnace to a smaller size that's more efficient and costs less to operate while providing the same level of comfort.

We hope you found these tips helpful! If you have questions about the performance of your furnace, seek out a qualified professional for an assessment—or to upgrade—to make sure you get the most out of your unit and can use energy wisely!

For more energy-saving tips, be sure to visit energy2030together.com/ourenergyuse.

published: Jan-24-2019