Some of the best built, most efficient furnaces available today
A properly installed Carrier furnace can make a huge difference to both your indoor comfort and your utility bills. Carrier furnaces are one of the best brands in the industry, and HVAC companies that sell Carrier products think very highly of them. And with efficiencies as high as 96% these furnaces are among the most efficient on the market.
Update for 2021: I recommend Carrier as a brand – but even more strongly, I recommend you consider purchasing a heat pump, rather than a furnace, because a heat pump will substantially reduce your carbon footprint relative to even the most energy efficient Carrier furnace or furnace of any brand. Luckily, Carrier also makes some very good heat pumps. My own experience switching from a 23-year-old Bryant furnace (Bryant and Carrier are different brands from the same company) to a high efficiency Carrier heat pump has been nothing but positive – installation went well, system operates well, and we’re saving money! Check out my entire section on heat pumps for more information.
The first thing to note with the Carrier line of furnaces is that it pays to shop around and find an HVAC company that knows what they are doing. If you read online customer reviews of the Carrier furnace line you may get the impression that these units are very failure prone. There are two points I want to make about online reviews of Carrier furnaces. First, people tend to write a Carrier furnace review when they are upset about a problem they’ve had either with the furnace, or the company servicing it. The masses of very satisfied Carrier furnace owners who have had years – even decades – of trouble-free operation aren’t going to go to the trouble of writing a review.
The second point is that it becomes quite clear, when you read these Carrier furnace reviews, that in the vast majority of cases the problems stem from either incorrect sizing (of the furnace itself, the ductwork, or the air intake and exhaust system), or faulty or shoddy installation. All of these are things your HVAC installer controls (or fails to control!) and if the contractor is poorly trained or cutting corners, you’ll get a system that is prone to failure.
Actual quality issues with the Carrier furnace
Before I go over specific product lines of Carrier furnace there is one real quality issue I’d like to touch on. In 1989, Carrier introduced a polypropylene-laminated secondary heat exchanger (also known as a condensing heat exchanger) into their high efficiency furnace line. Many customers experienced premature failure of the heat exchanger, and class action lawsuits were filed in Washington state (2005), and Wisconsin and Ontario (both 2006) alleging that these heat exchangers were causing Carrier furnaces to fail well before the expected 20+ year lifetime of the heat exchanger. The industry standard for manufacturing furnace heat exchangers is to use stainless steel, because of its corrosion resistance (the byproducts of natural gas combustion are highly corrosive). By switching to a polypropylene laminated heat exchanger, Carrier was able to avoid the corrosion problems but use a milder, cheaper form of steel. Unfortunately, the polypropylene had a tendency to separate from the steel due to the high temperatures of the combustion gases, which resulted in many heat exchangers suffering extremely high levels of corrosion.
The courts reached a settlement with the manufacturer, for all US and Canadian owners of Carrier furnace models affected by the heat exchanger problem. The settlement provides for an enhanced 20-year heat exchanger warranty (free service, free parts) for customers whose furnaces have not yet failed, and a cash reimbursement of up to $270 US for customers who have already had to pay for repairs to the heat exchanger. It’s important to note the free service, free parts aspect of the settlement – many Carrier furnace owners who learned about the settlements through their HVAC contractor were not informed of the ‘free service’ part of the deal, and were charged a hefty installation fee by the contractor. As for customers who already paid for the replacement themselves, the $270 cash reimbursement is based on a sliding scale (furnaces under 13 years old get the full amount, while furnaces older than that get less the older they are), and the cash reimbursement probably doesn’t come close to covering the $800-1200 cost that many homeowners report being forced to pay.
The settlement, by the way, applies to four different brands of furnace made by United Technologies Corporation, the owner of the Carrier brand: Carrier, Bryant (the furnace I own), Payne, and Day & Night.
Of course if you had the foresight to buy an annual service and maintenance contract for your Carrier furnace (as I did for my Bryant), and you renew it every year, the only issue you’ll have to worry about as far as this heat exchanger problem goes, is the actual failure itself, not the cost of replacing it.
A cracked heat exchanger is a very common problem in furnaces. Again, incorrect sizing plays a major role in heat exchanger failure, as I’ll explain later, so the high number of Carrier furnace heat exchanger failures may well be due to the combination of oversized furnace installation and the polypropylene heat exchanger design.
But do bear in mind that a cracked heat exchanger is both inconvenient and potentially life-threatening. A cracked heat exchanger can result in gases escaping the combustion chamber and spreading into the home, and since carbon monoxide is one of the byproducts of combustion, there is a risk of carbon monoxide poisoning. You should always ensure you have a working carbon monoxide detector in each of your home’s bedrooms – regardless of the furnace you own. In fact in more and more jurisdictions a CO detector is mandatory whenever you build a new home, renovate an existing home, or rent out a home or apartment.
High and mid efficiency Carrier furnace models
The current line of Carrier furnace models spans the mid- to high-efficiency end of the market. Note that a ‘mid-efficiency’ furnace means one that is at least 80% efficient, because many older furnaces currently in operation can be only 50% or 60% efficient. However, in the US today, all new furnaces offered for sale must be at least 80% efficient, so if you’re thinking of buying an 80% efficient Carrier furnace you are really buying the least efficient type of furnace currently available. My recommendation is to get at least a 90% efficient furnace, and preferably 95% or 96%.
Carrier makes four lines of furnaces: The Infinity line, the Performance line, the Comfort line, and the Base line. All four lines offer models starting at the bottom end of the range – 80% AFUE (annual fuel utilization efficiency), ranging up to 92% (Base), 95% (Comfort and Performance), and 96.6% (Infinity). The Infinity line comes with specialized control features described below; most other features such as a variable speed fan (improves energy efficiency and reduces noise), media filter cabinet, humidifier compatibility, and noise reduction technology, are available in different forms in different models based largely on efficiency, with the more efficient models offering more of these advanced features.
Carrier Infinity ICS furnace
The top of the line Carrier furnace is the Infinity ICS. This furnace offers 95% AFUE, and is reportedly the quietest furnace on the market. Models range from 60,000 BTU to 120,000 BTU. Each Infinity ICS Carrier furnace has two heat exchangers. The primary heat exchanger extracts 80% of the heat (which is what most mid-efficiency furnaces deliver overall). The secondary heat exchanger extracts an additionaly 12-16%, meaning that only 4% to 8% of the heat from the natural gas or propane combustion goes out the exhaust vent.
I have a section further down on Carrier furnace noise levels – see below.
What sets the Infinity ICS line apart from other Carrier furnace models is its comfort control technology. These furnaces support or come standard with three features that are available only on Infinity ICS, and a fourth that is available on a small number of other Carrier models. The first feature is Infinity Control, which is like a top-of-the-line programmable thermostat. It not only lets you set temperatures for different time periods on each day of the week (so you can have a toasty warm house when you’re active within the house, but lower temperatures for sleeping or while you’re away at work), but can let you control fan speed and humidity, while it also monitors and keeps you informed of air quality issues, filter condition, and other maintenance reminders.
The Infinity ICS can even detect, based on air pressure within the furnace ductwork, when the furnace filter has become too clogged and needs replacement. Since clogged filters are a common cause of reduced efficiency (and over time increase the wear and tear on furnace components) this feature is definitely helpful if you tend to forget to change your filter, or live in a very dust-prone or dander-prone house.
Some models of Infinity Control also support remote phone or Internet access so you can go on holiday and set the furnace low, then turn the heat up from afar before you head home.
The second feature is Comfort Heat technology, which consistently keeps your home within 3/10 of a degree of the thermostat setting. This not only maintains a constant level of comfort but means you benefit from the higher efficiency and lower noise level of the furnace running on its lower setting. Most furnaces have up to a 3 degree range between the low temperature that causes the furnace to kick in, and the high temperature that tells the furnace to shut off (this is based on the thermostat used). The Infinity Comfort system continuously monitors room temperature and furnace operation to vary heat output and fan speed so that there are fewer on-and-off cycles and a more steady, lower-speed operation (furnaces tend to be more efficient at lower operating levels).
Carrier furnace Comfort Heat technology is available both on the Infinity ICS line and on the Performance 93, Performance 80, and Boost 90 furnaces. (Note that the model numbers closely match the AFUE of each furnace, so the Performance 80 is actually one of the least efficient furnaces on the market.)
From a comfort perspective I’m personally not that excited about this Comfort Heat feature of the Carrier furnace, as I’ve never noticed that a 3 degree difference in temperatures over the course of my furnace heating cycle made that much difference to my comfort. But it does help the Infinity ICS deliver quieter performance at a higher operating efficiency, and with less wear and tear on componentry, since every time a furnace blasts on or shuts down there are sudden swings in temperature of the heat exchangers and combustion chamber, and sudden start-up of the fan motor, and the more such swings there are, the shorter the expected life of the components. (In fact I wonder if the heat exchanger failures people experienced that resulted in class action lawsuits were not entirely Carrier’s fault – if some Carrier furnaces were over-sized for the space they heated, as furnaces often are, it could result in more frequent cycling of the furnaces which would wear their heat exchangers out more quickly.)
The Infinity ICS Carrier furnace also offers the Ideal Humidity System which is just a somewhat fancier form of humidity control than you’ll get with a standard furnace humidifier. It controls humidity both when the furnace is running and when the furnace is ‘resting’ (not producing heat) but the fan is still blowing. But this seems like a feature in search of a purpose, since most people who have furnace humidifiers are plenty comfortable without it: unless your house leaks air like a sieve, most of the moisture introduced by the furnace humidifier during the heating cycle is going to stay inside the building envelope until the next heating cycle twenty minutes or two hours later (depending on outdoor temperatures).
The fourth special feature of the Infinity ICS Carrier furnace is its advanced diagnostics that allow it to download information to a laptop or PDA to make it easier to do problem determination on the unit. Most other Carrier furnace models come with a simpler diagnostic system consisting of a flashing light (with long and short flashes that combine to form a diagnostic code). This feature will help a Carrier furnace technician more quickly diagnose problems with your furnace (hopefully you won’t have any) but I am not convinced this is much of a value to the consumer.
But the Infinity ICS has one thing above all going for it: efficiency. Not only does it offer 95% Annual Fuel Utilization Efficiency – meaning that 95% of the heat from the natural gas or propane it burnswarms your house instead of going out the exhaust pipe – but it uses less electricity than almost any other furnace on the market. Gas furnaces use electricity primarily to run the blower motor. The Infinity ICS does likewise but uses a small fraction of what most other furnaces use – a typical furnace might use 500-625 watts of power while the fan is active, while the Infinity ICS uses only 100 watts while in operation.
What does this difference mean? In a cold December your furnace might run for 2/3 of the time, or 16 hours a day; that means you’d be using 1.6 kwh of power per day with the Infinity ICS, compared to 8-10 kwh/day for a standard furnace. That’s roughly an extra $1-2 a day in electricity costs, which might become $100-200 a heatingseason.
Carrier furnace noise levels
It’s interesting to note the wide range that the Carrier furnace models have in terms of noise level. Noise can be measured in decibels; a decibel level of 30 corresponds to a person whispering; a decibel level of 40 is that of a refrigerator; while a level of 60 is the volume of a conversation. Carrier furnace noise levels fall between the range of 40 and 60, with the Infinity ICS furnace at the bottom – a nearly silent 42 decibels. You might think the Infinity line would be the quietest of the model lines, but in fact the ratings are intermixed between model lines, with the Inifinity line being typically quieter, the Comfort line being typically noiser, and the Performance line somewhere in the middle. The following graph shows select Carrier furnace noise levels in decibels:
It seems like quite a range, but bear in mind that even the loudest model shown, the Comfort 92, is still quieter than a refrigerator. I’ve heard some furnaces that clunk and churn away very loudly (including the old oil furnace we replaced in 1998 with a super-quiet Bryant 355MAV Plus90i). The noise level of a refrigerator would be a welcome change if you’re used to an old clunker like that!
I’ve described the Infinity ICS in detail; this really is one of the very best furnaces on the market. In fact, according to one HVAC dealer, the Infinity line in general is hands down the best product on the market.
Tying an Infinity furnace to an Infinity heat pump
The Infinity ICS (and the Infinity 96) can be interconnected with an Infinity heat pump. This provides:
- Cooling and dehumidification from the heat pump in hot weather
- Heating and dehumidification from the heat pump in cool to mild weather
- Heating from the furnace in cold weather.
Heat pumps are an efficient way of heating at temperature ranges of around 40F and up, but become increasingly inefficient as temperatures drop below 40F. By combining a Carrier furnace and Carrier heat pump you get an air conditioner, and the most efficient heating source for both cool and super-cold weather! The Infinity control system takes care of the switchover between heat pump and furnace as outdoor temperatures fluctuate between the range where heat pump is more efficient, and those where a furnace is needed.
Update for 2021: While it is still true that heat pumps decrease in efficiency as outdoor temperatures drop, heat pumps, including the Carrier Infinity heat pump, have become much more efficient at lower temperatures since I wrote this article over a decade ago. Heat pumps are now more efficient than electrical resistance heaters (think, baseboard or portable electric heater) at temperatures as low as 1F / -17C. So rather than interconnecting a furnace with a heat pump, the newer approach is, just buy a heat pump! That’s what I did in 2020 – see my Carrier Infinity Heat Pump article for more information.
Other Infinity line models
What do the other Infinity line Carrier furnaces offer?
All Infinity furnaces come standard with a media filter cabinet – a space for a large air filter that does a far better job of filtering out dust and dander than a typical furnace filter. I have a similar cabinet in my Bryant Plus90i – an AprilAire media filter cabinet. While most furnace filters need to be changed once a month, my AprilAire filter only gets changed once a year, and sometimes it lasts two years before the technician from my HVAC service decides it needs replacing.
The Infinity 96 offers from 92.7% up to 96.6% AFUE – the higher-end figure being even better from a fuel efficiency perspective than the Infinity ICS, but it may not offer the same savings on electricity consumption. Like all models in the Infinity line the Infinity 96 supports the Infinity controls mentioned above. For a smaller home you may not have a choice of the Infinity ICS, which comes in models rated for 60,000 to 120,000 BTU; the Infinity 96 has a 40,000 BTU model. Remember, bigger is not necessarily better: if you install a higher-BTU model than your home actually needs, based on its size, insulation levels, and local climate, you can prematurely ruin your furnace due to the frequent cycling of the furnace, which will produce so much heat at once that it will shut down barely after starting.
One minor difference between the Infinity ICS and Infinity ICS is the gas valve. The Infinity ICS features a modulating gas valve, which means it can continually adjust the flow rate of gas based on demand, giving it multiple heating capacities – heavy on extra cold days, light on mild days, and somewhere in between when it’s cold but not freezing. The Infinity 96 has a two stage gas valve, which provides similar features but in only two ranges – high and low.
The Infinity 80 offers similar features to the ICS and 96, but of course has a significantly lower overall efficiency, higher noise levels, and is not ENERGY STAR qualifying, meaning any rebates you might get for installing an ENERGY STAR furnace are not available for this Carrier furnace. Also, instead of a lifetime warranty on the primary heat exchanger, the Infinity 80 offers a 20-year warranty.
Performance line of Carrier furnaces
The Performance line of Carrier furnace is quite similar to the Infinity line with the exception that the Performance line furnaces are not compatible with Infinity controls. They are compatible with an Edge Thermidistat which controls both temperature and humidity, and provides some of the features of the Infinity control but not all. The Edge Thermidistat provides ventiliation and fan speed control, as well as 7-day programmability (some models), but lacks remote system access, air quality control, and support for different temperatures in different zones of your house. Performance furnaces also lack the Ideal Humidity system and advanced diagnostics of the Infinity series, but as I mentioned earlier I don’t think either of these are terribly valuable features.
The Performance 95 and 96 furnaces do not come standard with a media filter cabinet, unlike the Infinity furnaces (the Performance 93 and Performance 80 do – go figure), but you can add one as an optional component.
Based on the added features of an Infinity 96 or Infinity ICS over a Performance 96 or Performance 95 (which both, oddly enough, are listed as 95% AFUE), I feel the Infinity line is a better first choice, but these extra features tend to raise Carrier furnace prices so if you don’t need the few extra features the Infinity line offers, the more efficient models of Performance Carrier furnace are well worth considering.
Boost, Comfort and Base Carrier furnaces
It’s not clear to me why Carrier carries five different lines of furnaces – Infinity, Performance, Boost, Comfort and Base – but the Boost series are similar to the Performance series except for the lack of variable speed motor. Efficiencies are 80% to 93% (Boost 80 and Boost 90) with the later being ENERGY STAR rated.
The Comfort series includes the Comfort 95, which has almost the same features as the Performance 95, except for its lack of multipoise design (which allows the furnace to be installed with airflow going up, down, or sideways.
The Base series comes in 92% and 80% efficiency models. Base models come with a single speed fan and are louder than any of the other models described – except for the Comfort 92, which is also rated around 58 decibels.
BTU rating ranges for the Boost, Comfort and Base are:
- Boost 80: 40-154,000 BTU
- Boost 90: 38,000 BTU only
- Base 80: 44-154,000 BTU
- Base 90: 40-138,000 BTU
- Comfort 80: 44-154,000 BTU
- Comfort 92: 60-120,000 BTU
- Comfort 95: 58-96,000 BTU
I sometimes wonder if the range of models is intended to create the illusion of competition within a single brand – instead of shopping around for one of many brands of furnace, if you’ve already accepted Carrier’s great reputation for quality and dependability, you’ll feel you’ve done a good job shopping around their own offerings. (And if that doesn’t work, the manufacturer may be hoping you’ll shop around at Bryant, Payne, or Night and Day!)
Quality problems with Carrier furnace installation
Let me reiterate that Carrier furnaces are among the best in the market according to most professional installers. The trouble is that some Carrier furnace installers or service technicians who do follow-up service aren’t properly trained in properly sizing a furnace for the home it goes into, designing adequate ductwork, or installing it in a way that ensures smooth operation.
The first problem to consider is sizing. Many factors go into sizing the BTU requirements for your furnace:
- The air volume of your home – usually computed just by looking at square footage, although looking at cubic footage makes more sense, since a house with 10 foot ceilings will take more energy to heat than one with seven foot ceilings!
- The state of insulation in your walls and ceiling – the poorer the insulation, the higher BTU rating you’ll need
- The state of draftproofing in your home – the more air gaps in cracked window panes, loose window putty, poor seals on doors and windows, cracks in walls, brick in need of pointing, and so on, the higher BTU rating you’ll need
- Local surroundings such as trees, other buildings, and weather factors such as typical wind speeds
- Local climate
As you can imagine, it can be a fair bit of work to come up with a proper sizing that carefully accounts for all the above factors. If an installer takes a few shortcuts and simply guesses at some of these factors – or all of them – they could be off in their estimate of BTU requirements by 50% or more. Since installers don’t want you calling them a month after the install complaining that your new furnace isn’t providing enough heat, they have a tendency to install a higher BTU furnace than you actually need (since a higher BTU furnace will always produce enough heat to keep you warm). And if you need a building or HVAC permit your local building department may insist on a higher BTU furnace than you actually need, because their simplistic formulas don’t factor in things like how much insulation you’ve added to your house, or perhaps the fact that you like to keep the temperature at a modest 65F in winter (my parents keep their house at 60F!).
But heating with too powerful a furnace has its downsides too:
- Shorter heating cycles – because the furnace puts off so much heat, it heats the place more quickly, causing the thermostat to shut the furnace down sooner.
- Greater temperature swings in some cases – because the thermostat may not shut off the furnace quite soon enough, it can actually get hotter than the thermostat setting.
- Significantly increased wear and tear on the fan motor and the heat exchangers due to repeated motor start and stop actions and sudden changes to heat exchanger temperature.
A second problem is installation errors. Installation can also involve short cuts and errors if your installer doesn’t know what they’re doing: if they design the replacement ductwork incorrectly, or on a new installation don’t install adequately sized cold air return ducts they may impede airflow through the furnace, increasing furnace heat build-up and resulting wear and reducing efficiency.
A third problem is maintenance by inexperienced personnel. I learned of this first hand – but fortunately was spared any ill effects from it – when I had my Bryant furnace installed. After a very professional install by an excellent HVAC company, the local gas company technician had to come by to sign off on its safe installation. He looked through the furnace manual to make sure things were installed according to the installation instructions. Then he asked me if he could borrow the manual to make a photocopy of it – so that on future service calls to gas company customers with this furnace model, he would know how to service it! Who would you trust more to service your furnace – the technician from the authorized Carrier dealership who has taken courses on serving their equipment and spends much of his working time servicing Carrier furnace models – or the gas company or independent technician who services everything under the sun?
Carrier does have more technology in their units than other manufacturers, which is how they get such high efficiency and great comfort and ease of use features. But if an installer doesn’t understand the technology, and messes something up in the installation, no amount of service calls will solve that. Up to 85% of failures are caused by faulty installation.
So always buy your Carrier furnace from an authorized Carrier dealer – and check their references first. And the same applies for getting service on an existing furnace, whether you had it installed, or bought a house with a Carrier furnace already installed: get a qualified Carrier technician to do your service.
I also strongly recommend getting the annual maintenance and service contract. For typically under $100 in the first ten years you’ll get a free annual servicing of your furnace as well as free parts and labor on any required repairs. The contract can be renewed after the tenth year for a higher price (since the warranty coverage typically decreases) but it’s still a bargain when you consider the maintenance is included and you are basically guaranteed a well-functioning furnace every heating season.
Don’t forget your own role in furnace maintenance
Remember to get your Carrier furnace serviced at the start of each heating season – both to ensure smooth operation, and to catch any potential problems before they get serious. But also remember that there’s a reason you hire qualified HVAC personnel to do your furnace maintenance – they know what they’re doing.
I read one customer complaint about a Carrier furnace that was installed with an improperly sloped exhaust vent. High-efficiency furnaces don’t pull air from inside the house or vent it up a chimney – instead they use 2″ PVC pipes to draw fresh air in from the outside, and vent exhaust air back outside. The exhaust air carries a fair bit of moisture, because when you burn natural gas with oxygen, the chief byproducts are carbon dioxide and water:
CH4 + 3 x O2 = CO2 + 2 x H20
(I remember that much from high school chemistry!)
If your exhaust pipe has a dip in it, water vapor condensing in the pipe may pool, and if the dip is big enough it may flood the pipe to the point where no air can flow through the pipe. I actually did this myself when my Bryant furnace was first installed: the installer strapped the pipes along the unfinished basement joists, and I didn’t like the fact that the pipe kept getting lower as it moved outward, so I put it up higher, and within an hour my furnace had shut down due to a water-blocked exhaust pipe. (Easily fixed once I knew the cause.)
Venting that is poorly done for areas that have a mercury dip of 0 C or 32 F, or colder will freeze up. Also any water vapor vent must be further away from the air intake vent to the furnace’s air gas chamber by three feet. This is B149 section 8.3.7 CSA gas and propane code, in Canada. Not sure what the code in the USA.
Some installation instructions put the two vents close together – within six inches. In my case the vents, both of them froze up. Also icy cold air through the outside air intake colder than 50 F caused no heat in the home. I am interested in a law firm who will take Lennox to a class action suit in Canada as they still have a too close air intake to a water vapor gas exhaust vent. Good for Carrier that they resolved some of their problems. Lennox seems too big to care.
Great write up!
My choice is:
Infinity 96 59TN6 $4700 installed
Performance 59TP6 $4350 installed
Which would you choose?
The Performance goes down to 40,000 BTU while the Infinity starts at 60,000 BTU. It depends how many BTU you need. My installer (back in 1997) recommended going with the 40,000 BTU for my house with about 1300 sqft of living space and 400 sqft of basement, in Toronto where the weather can often drop to -15C/5F at night, and sometimes as low as -30C/-22F. We’ve never had a problem keeping warm (in a 100-year-old house that has been retrofit with extra insulation, new windows etc.).
They are both “Up to 96.7%” efficient. The only differences I can find in their specs (other than the BTU) are that the Infinity has a higher degree of electrical efficiency, and allows 4 choices of “constant on” operation, which I guess means you can set the fan to run continuously at different speeds (good to keep air circulating).
I would ask the installer about the differences and decide if those differences are really worth the $350. Electricity prices seem to keep going up even as oil prices plummet, so if the Infinity will save you $20 a year in electrical costs, then over a 20-year expected lifetime of the furnace, you are still better off with the higher priced one.
I have old furnace in a small area, it says “Carrier Performance 80” on it. I considered it very very noisy. When it turns on , we have to increase the volume on the TV and I wake up when it turns on in the morning. How noisy is Performance 80 compared to Infinity 96? Is it worth installing Infinity 96 just to reduce the noise?
If your furnace is so loud that you have to turn up the TV, there is probably something wrong with the fan. My own furnace is 20 years old and the fan is getting noisier. I can’t find noise specifications for the Carrier Performance 80 so can’t compare it to the Infinity 96, but the Infinity 96 is advertised as very quiet. It’s worth having a technician look at the old furnace to determine the source of the noise, especially if you’re already on an annual maintenance contract, but if the furnace is more than 15 years old it’s already approaching its end of life, you might want to just replace it. The other benefit of the Infinity 96 is that it’s much more efficient.