38

Is A Two Stage Furnace Worth It?

A common question when someone needs to replace their furnace is whether to choose a single stage or two stage furnace.

Most people pay very little attention to their furnace. The first time we even hear the option of two stage heating is from a contractor’s salesman. Often these salesman wax poetic about how much better a two stage furnace is over a single stage furnace.

But before you choose, I’d like to give you my real world experience with these furnaces. You’ll find it quite different from what salesmen are telling you.

More...

What Is A Two Stage Furnace?

Two stage heating describes a furnace with two levels of heating output. First stage (low fire) will run between 70-80% of the rated capacity of the furnace. When a furnace initially turns on it will start in this low fire mode.

The furnace will go to second stage (high fire) based on one of two conditions. 1) The time the furnace has been operating or 2) if the thermostat senses it needs to raise the temperature more than two degrees.

For example, when a furnace rated at 80,000 BTU’s first turns on it will operate at 60,000 BTU’s (75% of 80,000). After running for 10 minutes the furnace will determine it is not keeping up with the need and switch to high fire to meet demand.

The difference between single stage and two stage furnace is the single stage furnace has only one heating output. If it's rated at 80,000 BTU's, it will only operate at that capacity.

Beware Of The Two Stage Furnace Hype

Certain heating contractors will rave about the claimed benefits of the two stage furnace. "It will save you money in utilities, be quieter and keep your home more comfortable" they'll claim.

At first, the two stage furnace might look attractive. After all, who doesn’t want those things. But does a two stage furnace really offer those benefits over a single stage furnace?

Is A Two Stage Furnace More Efficient?

A two stage furnace is NOT more efficient than a single stage furnace. It will not save you any money on your utility bills compared to a single stage furnace.

Furnace manufacturers do not claim there is an efficiency gain with two stage furnaces. That idea often comes from unethical contractors trying to sell more equipment.

Efficiency is determined by heat exchanger design. Single stage and two stage furnaces of the same efficiency style use the exact same heat exchanger.

In other words, a 95% efficient furnace is 95% efficient whether its running in low or high fire. No savings.

Is A Two Stage Furnace Quieter?

Yes. But so is any new furnace compared to the old clunkers we've had in our homes for the past 30 years.

In addition, most of the noise that we complain about comes from the amount of air that is circulating through the duct work. Whether your furnace is two stage or a single stage, the required amount of air needed for the furnace to operate properly will be the same.

Does A Two Stage Furnace Keep You More Comfortable?

Who doesn’t want a more comfortable home? The two stage furnace claims it creates this by helping prevent temperature swings. How? By running at 70-80% of it’s rated capacity in first stage, the furnace will run longer thus reducing temperature swings.

The idea seems plausible but the field tested numbers do not support this claim. Here’s an example:

Let’s use an 80,000 BTU furnace as an example. If the airflow is set properly this furnace would raise the temperature of the air circulating through it about 50°. (Ex: 70° air coming into the furnace, 120° out to the supply ductwork)

At 75% capacity the furnace would be burning 60,000 BTU’s. Although heat output is changing, if the airflow is set properly the temperature of the air at 75% capacity would be only 7°-10° lower.

It would be difficult for anyone to notice that small of a change. It also ends up having little effect on the run-time of the furnace or temperature swings.

Single Stage Versus Two Stage Furnace

A single stage furnace has two major advantages over a two stage furnace. They are less prone to breakdown and cost less to repair.

The parts are also tend to be more universal. A heating contractor working on your furnace in twenty years will be more likely to find needed parts. This also helps to get your furnace up and running quickly in the event you do need a repair.

Are there any two stage furnace benefits? After digging past all the marketing it’s easy to see that a two stage furnace does not have any benefits over a single stage furnace.

Now you’re asking “If the two stage furnace doesn't save me money or make my home more comfortable why should I spend the extra money?” The answer is you shouldn’t.

Keep this in mind when deciding between a single stage or two stage furnace: A new single stage furnace installed by a good heating contractor will keep you comfortable just as well as a two stage furnace.

Why The Push For Two Stage?

Contractors often put in two stage furnaces because they’re either lazy or not very good.

Rather than taking the time to do a proper calculation to determine the correct size furnace for your home, they install an oversized furnace.

They figure the low fire mode on the two stage furnace will make up for their poor workmanship. It doesn’t and creates a host of other problems.

Manufacturers on the other hand push features that have benefit only for themselves. They’ve tried for years to improve profits by having higher equipment turnover.

They need furnaces to fail after 10-20 years not 20-30. They have succeeded by adding expensive and repair prone features all while telling you its for your benefit.

Two stage furnaces are designed to fail earlier. They won't fall apart sooner than a single stage furnace. But repairs on a two stage furnace in the 10-20 year mark will cost considerably more.

Replace the furnace or pay for high mark up parts. Either way manufacturers and unethical contractors win.

Manufacturers have done the same thing with a feature called variable speed. In fact, a two stage variable speed gas furnace is often sold as their "best" furnace.

You can avoid the manufacturers trap though. Don’t focus on equipment options. Focus on choosing the right contractor. Nothing is more important.

You will be happy with any single stage furnace as long as it's installed by a good contractor. And a good contractor won’t recommend features that you don’t need.

If you want more information on how to find good contractors click here.

Share the Love
Click Here to Leave a Comment Below 38 comments
Rodney Messinger - a couple of years ago

Thanks a lot. Your information was very helpful. After 30 years of the same oil furnace it was time to switch to a natural gas furnace. The decision was between a single or double stage furnace. Reading your article it was a know brainer. Thanks

Reply
    Robert - a couple of years ago

    Glad you enjoyed the information, Rodney!

    Reply
Maggie - a couple of years ago

Glad I read the article

Reply
andy mather - a couple of years ago

Well thank you for this article. We have a 30 year old furnace that has really given us no problems. However, we want air conditioning and so if we are doing one we decided to do both. We have been given three bids one salesman in particular was pushing a class 2 high priced unit about 2k more than the others. He also mentioned dry air and allergies trying to upsell a new humidifier and electronic air cleaner. This article has just made our decision so much easier.

I am a home renovation contractor and until doing our research I was completely lost on this issue. Now we have go choose between Lennox and Trane or go with the cheaper model made by Coleman???? Single stage of course!

thanks andy

Reply
Robert Hammel - a couple of years ago

Thank you for this. I’m just putting a new system in and this was helpful I’ve wondered why many sales people and places online claim a two stage would be more fuel efficient — which seems illogical given the parameters of a fairly “closed system”.

Reply
    Robert - a couple of years ago

    I’m glad you found it helpful. Thank you Robert!

    Reply
Lenore - a couple of years ago

What do you think of the x13 torque motor used in furnaces?

Tks.

Reply
Tino - a couple of years ago

Thank you , great article. I was wondering what size furnace I would need, mine is a 35 year old ICS 90,000 btu @ 80 % efficiency in a 2000 sq ft 1981 house with newer windows in Toronto, Ontario. It really doesn’t use a lot of gas but I believe it is near it’s end of life. I have had quotes for 80,000 and 60,000 btu @ 97%. The contractor who quoted me the 60,000 btu was sure thats all what my house needs. Neither did a load cal.

Thank you in advance.

Reply
    Robert - a couple of years ago

    Hi Tino – I wish I was able to tell you what size furnace you need but there are just too many factors that require a physical evaluation to make that determination. What I can tell you is this; the most important aspect with regard to the size of the equipment is a performance guarantee in writing from the contractor. As an example: “Your furnace will keep your home at 70° when the outdoor temperature is at 0° or we will replace it for free.” Go with the contractor that stands behind their work in writing.

    Reply
      Tino - a couple of years ago

      Thank you I will ask for that in writing.

      Reply
mike - a couple of years ago

Thank you for clearing this up. The info was very useful and makes a lot of cents :0

Reply
    Robert - a couple of years ago

    Happy that I could help Mike.

    Reply
Patti - last year

Is there any truth to what I’ve heard about a two stage furnace being better for really cold climates? I live in Chicago and need a new furnace but money is really tight and I don’t want to get sucked into features I don’t need.

Reply
    Robert - last year

    Good question Patti. First I would tell you that no one NEEDS two stage equipment. Your current system is most likely single stage and if it’s sized properly kept you comfortable in the winter. Second, a home in a colder climate will not increase the reasons to buy two stage equipment. If anything it would go the other way. Two stage furnaces are marketed to help durning milder weather when you don’t need the full BTU’s of your heating system. You’re more likely to need the full output of your furnace in a colder climate. Hope this helps you save some money!

    Reply
Margaret - last year

Thank you so much for this article. I have been searching in vain for objective information online about the pros and cons of single versus 2 stage gas furnaces, and yours is a lone but compelling voice of reason in the wilderness. It seems clear that the utilities, manufacturers and contractors are well aligned in promoting the “better efficiency” hype for 2 stage furnaces. It’s a real struggle for the homeowner/consumer to sort out fact from fiction, especially since 2 stage furnaces haven’t even been around long enough to assess their true lifetime/out of warranty repair costs. In my area (Pacific Northwest) our utility will not rebate for any efficiency below Energy Star level, even though a minimum 92% efficiency is already mandated by the Canadian government. HVAC quotes are structured so that the single stage is more expensive than the supposedly superior 2 stage! A single stage furnace has served my needs adequately for 30 years, and I’ve no desire to have a furnace and fan running continually in my house all day long no matter how quiet. The “better comfort” claim is purely subjective and depends entirely on the occupants’ personal heating habits and preferences, house size and layout, other heat sources, and so many other factors. If a contractor pushes the “higher efficiency” claim for 2 stage furnaces, show them this ASHRAE study whose results indicate that two-stage technology by itself does not save energy: https://aceee.org/files/proceedings/2006/data/papers/SS06_Panel1_Paper16.pdf

Reply
    Robert - last year

    Hi Margaret,

    Thank you for your kind words. I’m glad you found the information helpful. And thank you for the ASHRAE study link. Hopefully more studies like this will be published that debunk the marketing hype.

    Reply
Glenn Stevens - last year

hi Robert

Good article, I’ve been researching furnaces for a little while now, a load calc of my house indicates I need a furnace with an output of approx. 63k btu’s. An 80k btu 92% furnace has an output of 73,600 btu’s 10k more than I need, and 60k btu 96% furnace has an output of 57,600 btu’s 6k less than i need. (80% AFUE furnaces are not sold here).
So the question is do I go over or under? A 2 stage 80k btu 96% offers a little bit less but more if I need it. In this case a 2 stage seems to be the answer.
What do you think? The 2 stage is only $300 more.

Reply
    Robert - last year

    Hi Glen,

    Glad you enjoyed the article. In answer to your question, I never recommend choosing a furnace sized lower than the calculated heat loss for your home. I also never recommend homeowners doing their own load calculations. They’re more complicated then you’d expect and free online programs that offer this service are terribly inaccurate. Make sure you choose a contractor that can do a proper load calculation for your home. Then the sizing of the equipment is their responsibility.

    Also, watch out for the seemingly low cost of $300 to “upgrade”. Manufacturers want you choosing 2 stage so down the road when it needs to be repaired more often and for a higher cost you’ll be forced to choose new equipment.

    Reply
Eva Richards - 11 months ago

thanks for always informing your clients on our do’s and dont’s
your information is invaluable to us

Reply
Lamont Swain - 8 months ago

I asked most of these questions of the new contractor, and he didn’t give any of these answers. Thank you very much for the information.

Reply
Russell OGDEN - a few months ago

Thank you for this detail, really helpful, i have qoutes for single and two stage options, the comfort claim has been touted but no real benefits other than that.

We are from overseas (UK) and the whole furnace thing is new to me so this has helped lots

I will be going with the single stage for sure.

Reply
    Robert - a few months ago

    Welcome to the States Russell! Glad the article was helpful.

    Reply
Steve - a few months ago

What a wonderfully honest article! I am a Professional Engineer and when I purchase a product I really get into reviewing product brochures, specifications and studies. Which as this article has clearly confirmed is a bunch of Industry “flush” and unrealistic product expectations. In my 30+ years of Engineering I go right to the Contractor for the real deal! The National Grid rebate being $420 for Two Stage versus only $140 for Single stage is what drew me into the Two Stage. Acting as clueless home owner I requested two quotes for High Efficiency furnaces from local HVAC Contractors. Both pushed 2 stage and blew off the single stage even when I asked about them. The I called in and HVAC guy that I have worked with for commercial HVAC inspections. Not a friend, just “good old boy” Contractor with 40 years experience. Good News!! He stated exactly what this article and your comments reflect! He won’t even install a 2 stage unless the owner insists and he makes it very clear of impending potential issues. Thank you so much for your article and comments. I will be having have a single Stage 96% being installed in a week or so.. As soon as I choose a new Hot Water Heater as mine will be Orphaned with the new High Efficiency Furnace… Now all I need is help with choosing a Power Vent or Tankless Water Heater :-) Do you have an article or a good source for honest info on that? Thanks Again!

Reply
    Robert - a few months ago

    Thank you Steve. I’m glad the article helped in your research.

    I don’t have an article about choosing a water heater but I’ll give you my short answer. If it’s an option my first choice would be to keep a standard water heater and install a liner in the chimney so it’s properly sized. If that’s not an option I’d recommend a power vent water heater over a tankless. Tankless have many disadvantages. 1) The savings and lifespan are GROSSLY overstated. 2) it requires annual maintenance (which can be costly) and 3) it WILL be more troublesome. There are other factors in your home that need to be considered so find a good contractor that you can trust. Hope this helps.

    Reply
Denise - a few months ago

Thank you for this article. I now have to replace my 20yr old gas furnace. My personal friend who is also a HVAC Contractor, altho what I would call a “green horn’, being in the business for only 5 yrs., and I am an old schooler. He strongly recommended against a 2 stage(fancy schmancy-his words), given his experience including his own home furnace. In researching gas furnace companies it seems I can’t get past the joys of 2 stage hype-which caused me to doubt my lovely green horn friend. You have confirmed his advice & provided me more schooling. Again, THANK YOU!!

Reply
Donald - a few months ago

I actually think 2-stage would solve some problems here. We have a house on one level, super-long runs, poorly insulated. In the coldest days it is demanding huge BTUs. Shoulder season it is OK and therefore sensitive to “blasting heat” syndrome. I think longer run times would balance out air distribution much better, keep the air in those crawlspace runs from getting cold before the next run, and yet manage the blasting heat issue well. Just- the oddities of our system.

Reply
Karen Markin - a few months ago

ksmarkin@gmail.com
I’ve had 4 contractors only one recommended a single stage furnace. We have an addition that never gets warm or cool enough. He said we need the stronger blower to get the heat into that room. Does this sound right to you? Do you recommend one single stage over another (Carrier, Bryant, American Standard).
Thanks for your help – great article!!!

Reply
Robin Faught - a couple of months ago

I just purchased a 2 stage furnace from One Hour Heating and Cooling. So far I hate it and want it out. They are coming again tomorrow, because I don’t understand the concept of this thing going on and off every 6/7 minutes. All I see is dollar signs for the electric bill. I just replaced my 40 year old furnace that was working, but thought it was costing me to much in gas, but now I’m thinking I jumped the gun and shouldn’t have done it. The guy that came out once already told me that it’s not going to cost me me in electrity that it’s like turning on a light. Well old school me hears my parents yelling at me to quick switching that light switch on and off or opening and closing the refridgerator. I hope they can replace this.

Reply
Jaylene Johnson - a couple of months ago

Hi there…really appreciate this article. We are dealing with a contractor who has an excellent reputation for integrity and customer service (and maintenance plan). He explained that the 2 stage furnace (versus the one stage) has a type of fan than can keep the air circulation going in the house for less cost (and that keeping a fan going is recommended for air quality?)…The choice is between a Goodman stage 1 furnace, or the lowest level stage 2 with the particular fan. I’d like to

I appreciated reading that the single stage might be sufficient for comfort in our home. We’ll be replacing a 25 year old Carrier unit, so I am thinking anything will be better than what we have currently. We are in a poorly insulated 1 1/2 story, sub zero temps 5-6 months a year, and 70s slider windows. Baseboard heat on second level, plus one vent from furnace.

Is air quality from a fan that runs frequently/constantly going to make it worth the extra $800 plus dollars?

Hope to hear from you soon.

Reply
    Robert - a couple of months ago

    Hi Jaylene – I’d recommend two things. 1) Take a look at this article here on why you would want to avoid a furnace with a DC motor (also called a variable speed motor). 2) Get a few more proposals and focus on finding the best contractor. They’ll help you choose the best furnace for your home.

    Reply
Jaylene Johnson - a couple of months ago

Further to my last email…the 2 stage goodman model (GMEC962 – 40,000 BTU) has a DC motor and is energy star rated…I’m not sure why this would be better than the 1 stage model (SS96 – not energy star rated and not DC motor) Claim is that we would save more in hydro bills than with single stage, and that the air quality would be better.

Again, 1 1/2 story home, replacing 25 year Carrier model. Baseboard on second level (only one vent upstairs)

Thanks!

Reply
dan - last month

So, So confusing. I just got an estimate for a 2 stage and single stage Trane furnace The 2 stage was highly recommended
by the contractor. I do trust these guys as they have been around for many years. Here’s the scoop, it’s an 80,000 BTU and
80% efficiency. My house is around 13 hundred square feet not including the unfinished basement. The house was built in the fifties and isn’t well insulated. It’s very drafty in the living area where we spend most of our time. The upstairs has two rooms with one vent in each room and no cold air returns. Would a 2 stage help keep a drafty room more comfortable, and
would the lower speed not heat the upstairs well.As it is now, we need a space heater to supplement the upstairs room. I have an 18 year old Armstrong single stage now and it’s still kicking ass with zero repairs so far. It’s getting up in age and was a little concerned with the 25 below temps last week in Chicago. The only reason I’m considering a 2 stage is once my furnace shuts off it’s chilly in ten minutes because of the draft. The 2 stage is around 600.00 more than the single stage.
Also, does 80,000 BTU’s sound about right for the info I gave? I would also get an AC unit with the new furnace. I’d like to
keep going with the Armstrong but am concerned with an expensive repair. The price I got was 6,100 for the 2 stage with a 2 ton 13 ser AC unit. Of course, minus 600.00 for a single stage.

Reply
STANLEY CAMSON - last month

Hey guys. Your website is very helpful. I have gotten a quote on a two stage. After reading your information I decided to go with a single stage. But I was surprised that there was only a 295.00 dollar difference. That does not seem right. What is your opinion

Reply
    Robert - last month

    Hi Stanley. Glad you found our information helpful. It’s true that there won’t be a huge difference in cost up front between single and two stage furnaces. The savings will add up down the road in the longer life of single stage equipment and lower costs to repair.

    Reply
Dan - 3 weeks ago

After rereading the threads, I went with a 60.000 BTU single stage. I’m very happy I did because a 2 stage would have been a waste of money. I’m glad I found this site and many thanks for all the great info. If I can still get the 10 year parts and labor for the sale price of 389.00, I might do it. The company has been around for 80 + years and isn’t going anywhere.

Reply
Elizabeth - last week

John, after a sleepless night, we’ve decided on a single stage furnace.
EVERYTHING I’ve read on-line suggests that 2-stage is the way to go, but the man installing our furnace stands behind his recommendation of a single-stage furnace, so we’re staying the course.
I’m concerned about cool spots, and about noise, but your article has convinced me that the 2-stage is not worth the additional investment.
Thank you!

Reply

Leave a Reply: