All About Furnaces: Efficiency, Cost, Repairs, & More

Written by Andy Stauffer

December 18

forced air system furnace
At Stauffer & Sons Construction, when we build new homes, 90% of the time, we use a forced air heating system (i.e. a furnace). This guest post is by Toby Conquest, "The Furnace Guy," who is the HVAC contractor we use for a majority of the homes we build. We hope you find the information he shares helpful, and as always, feel free to contact us with any questions.

Q: First things first: you call yourself “The Furnace Guy.” Why do you prefer furnaces over other home heating systems?

A: I actually do just about everything: in addition to forced air (furnaces), I install in-floor radiant heat, baseboard heaters, and even radiators (which can use either steam or water). However, I prefer forced air heating systems over others because if I can get my hands on the air inside your house, I can control the indoor air quality. With a system that moves air through the home, there’s so much you can do with it: filter it, humidify it, kill germs with ultraviolet light, and more.

Q: Can you explain furnace “efficiency ratings”? How important is a rating when buying a heating system?

A: An efficiency rating, (technically called “Annual Fuel-Utilization-Efficiency,” or “AFUE Rating”) measures how efficient a furnace is in its fuel consumption. In the most basic terms, that means if you have an 80% efficient furnace, for every dollar of fuel you put into it, $0.80 is used to heat your home, and $0.20 goes through the vent right out of your roof. Legally, in Colorado, the minimum I can install is an 80% efficient furnace. It goes up from there, but obviously, as the efficiency rating increases, so does the cost.

Ratings are important and efficiency is important, but ultimately you have to decide what’s most important to you. Heating and cooling systems come in a wide range of prices, and I tell people that if you’re in the market for a car, you can buy a Geo Metro, or an Aston Martin, or anything in between. The same is true for furnaces, the furnace you should get depends on your needs, budget, etc.

Some people think I’m always going to try to sell them the most expensive system on the market. But that’s not true: I remind people that your home heating system will only be as efficient as your windows and ceiling. You can have the most efficient furnace out there, but if you have leaky windows or a poorly insulated attic, you’re just wasting money since all that heat is escaping. People often think that in order to lower their gas bill, they need to buy a more expensive furnace, but in real life, the amount of heat that will leak through the ceiling and windows is the same no matter what your furnace’s rating is.

Q: On that note, what type of furnace provides the best “bang for your buck”?

A: It depends on whether you’re installing a furnace in a new home, or replacing an old furnace in an existing home.

When you’re starting from the ground up with a new home, it’s much easier to prepare the house for a higher efficiency furnace at the beginning. For a new home, I recommend a 92% efficient furnace at a minimum, but I prefer to go to at least 95% because then you can get a two-stage gas valve with a DC drive motor which offers incredible efficiency (more on two-stage valves and DC motors later).

When replacing an old furnace, you’re limited by many things, such as the amount of space you have in the mechanical room, the existing duct work, and more. Having said that, I tell people the best bang for your buck when replacing an old furnace is an 80% two-stage furnace with a variable speed DC motor.

Q: How much does a furnace cost, generally speaking?

A: That’s hard to say because it obviously depends on a lot of factors. In a new home, the total cost will be based on the square footage of the home, and the duct work you install. Most of the forced air systems I do for Stauffer & Sons Construction are in the $10,000-20,000k range.

For a change out (replacing an old furnace), the cost depends on a different set of factors such as: code issues or upgrades you might need, whether you’re replacing “like with like” or upgrading to a better system, etc. Generally, though, if it’s a simple replacement with a furnace similar to the old one, it can be as low as $2,000-$5,000. But if you’re going from a very old furnace to a new, highly efficient one, it could cost much more, maybe $10,000 or $12,000. That’s mainly because once you pass the 90% threshold, you can’t use a metal vent anymore, since the flue fills with condensation, so you need a PVC vent. This requires some serious retrofitting with drywall, roofing, and framing work before you can install it.

Q: How are furnaces powered?

A: There are a few different ways to power a furnace:

Natural Gas: natural gas is the most common, and in Colorado Springs, many neighborhoods are already set up for this. You just plug right into the gas lines in the house.

Liquid Propane (LP): propane works just like natural gas, but is slightly more efficient because it runs hotter per CF (cubic foot). One drawback to propane is that it’s more expensive, and you need a storage tank to hold it.

Electricity: an electric furnace is technically called an “air handler.” It looks very similar to a furnace but instead of having a gas fuel train, it has electric heating strips above the blower.

Q: How often do furnaces need to be serviced, and what happens during a service?

A: What we do when performing a “service and clean” on a furnace is replace the filter and do a safety check. A safety check can include testing for carbon monoxide, looking for gas leaks, checking for any issues with electrical connections, or finding lost efficiency.

The frequency depends on the number of hours it’s been used, but the rule of thumb is to get your furnace serviced once a year. One of the big benefits of getting your furnace serviced is that a furnace tech can look at your system and see if you have any parts that have failed or are about to fail. This is important: if I can prove that a particular part is about to fail, and you are four years and eight months into a five-year warranty, I may be able to replace that part under warranty. When that happens, I’ve just been able to save you the trouble and expense of having to call for a repair when the part does fail, especially if it’s after the warranty expires.

Q: What kinds of parts break on a furnace, and what do repairs cost?

A: The parts that most commonly wear out are as follows:

  • Hot surface igniters. These cost around $100, so it’s not an expensive repair.
  • Inducer motors. This motor powers the smaller blower that pushes carbon monoxide out of the vent. These can cost $200-600 depending on the brand and efficiency so it’s also not an expensive repair.
  • Blower motors. AC motors, as I mentioned, wear out quickly, since they’re not very efficient, and they run very hot. I’ve seen AC motors fail as soon as one year after installation, but I have never seen a DC motor last less than ten years. Cost: $250-750.
  • Thermocouples. You see these on older furnaces, but they’re not very expensive (about $30).

Q: Aside from just buying a high powered furnace, are there some home improvement projects people can do to reduce their heating bills?

A: There are a few things you can do (outside of spending more money on a new system) to help save money and increase the efficiency.

  1. Replace your windows. As I mentioned before, no matter how efficient your heating system is, if you have windows that leak heat out of them, you’re going to waste money. I replaced the windows in my own house: I now have Low-E two-pane vinyl windows. This is money well spent.
  2. Add more insulation to your attic. This is simple and cost-effective. I also did this in my house: I have double blown-in R70 insulation in the attic. This is a very easy and cost-effective DIY project: you can rent a machine at The Home Depot and do it in an afternoon for less than $1,000.

The other thing you can do is build a new custom home. Really. That’s why people hire high-end custom home builders like Stauffer & Sons: Andy Stauffer specializes in making each home completely comfortable and intelligently designed for each client. I really like that; that’s why I don’t do any heating and cooling for tract home builders. I prefer to work with builders that address each individual family’s lifestyle and what works specifically for them because that’s who they’re building the home for. And I think that’s part of why custom builders like working with me: when I get a set of plans for a new home, I look carefully at what is specified for the project, including: how tight the construction is, the type of windows that will be used, whether the walls have only sheeting or a plastic membrane, whether there’s spray foam, what kind of roof there is, how many people will live in the home, whether it’s an EnergyStar or LEED home, etc. Knowing this allows me to know customize the proper heating and cooling system, and decide the number of air exchanges per hour you’ll want, and more.

Q: Aside from the furnace, are there any other parts to a heating system people should be aware of?

A: In Colorado Springs, our relative humidity is very low, usually around 35% in the summer, which makes it quite comfortable. But in the winter, the problem is that when we heat the air in our homes, the process reduces the humidity drastically, all the way down to as low as 5% relative humidity. This extremely dry air can cause nosebleeds, and static electricity can build up in your home. So I recommend adding a humidifier if you can. It’s a separate device that connects to your furnace, and it doesn’t cost a lot.

Q: Are there any new technological advances in heating systems that people should know about?

A: It’s amazing: the heating and cooling industry has changed more in the last five years than it has in the fifty years before that. It’s moving very quickly now. Everybody’s talking about “smart thermostats now,” and while I like them, in my opinion, the two greatest advances we have now are 1) the two-stage gas valve, and 2) the DC drive motor.

I really like two-stage gas valves: most gas valves on the market are either 100% on or 100% off; hence, the name “one-stage” valve. Why is this bad? It’s like getting into your car and pushing your gas pedal to the metal every time you drive, and then turning it off. There’s no middle ground in between. But with a two-stage valve, it can run at half capacity. So for quick math, if you have a 100,000 BTU unit, it can now run in low-fire mode at 50,000 BTUs, and the longer you can run in that mode, the more efficient it is.

The DC (direct current) motor is a great advancement because it’s “smart”—it can actually sense resistance. It feels how hard it’s pushing the blower and can ramp itself up and down as it needs to. The standard AC (alternating current) motor runs at higher amps and a much higher temperature. An AC motor runs around 9 amps of electricity while a DC motor only uses around 1 amp. Of course, though, the DC motor is more expensive. But I’m a big fan since it’s so much more efficient and lasts much, much longer.

One thing to be aware of, though, with all these new furnaces we have today: having more bells and whistles means more moving parts. More moving parts means there’s more to break. And since these parts do so much more than they used to, they’re more expensive to replace. For example, instead of having a plain metal case with a blower wheel, these days we have a plastic case that’s made to handle moisture and has a place for condensate to go, etc.

Disclaimer: the views, opinions, and positions expressed on this blog post do not necessarily reflect the views or opinions of Stauffer & Sons Construction and are not intended as legal or professional advice. All information deemed reliable but not guaranteed. For more information, please review our website terms of use.


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