Energy saving furnace
You'll pay less overall, if you pay more up front
An energy saving furnace can be one of the best investments you can make in terms of cutting your carbon footprint, reducing your home energy bills, and saving money.
Twelve years ago I moved into a 77-year-old house. I knew I needed to get an energy saving furnace installed. Our home inspector guessed that the old oil furnace was no more than 50% efficient, and the previous owner's utility bills certainly showed that - over $1,300 a year in oil costs, in 1997.
Going for a new oil furnace wasn't really an option, even though there were high efficiency oil furnaces available even then. Why? Because many home insurers would not issue a new policy to a home with an oil furnace, due to the risks of environmental contamination from a leaking tank. I knew electric heaters are much more costly to operate than natural gas, so I decided to pay to have a gas line installed from the local gas utility, and to look for a forced air natural gas furnace.
Having been obsessed by energy efficiency since about the age of fifteen (when I built my first wind generator in shop class) I decided to pursue the most energy saving furnace I could find. At that time, Bryant had a very good reputation and made some of the most efficient gas furnaces on the market. The unit I bought had an advertised Annual Fuel Utilization Efficiency or AFUE of 94%, which means that over the course of a typical year, 94% of the heat produced by the furnace goes towards heating the air in the ducts, and only 6% escapes to the out of doors with the exhaust gases. There are currently low-, mid-, and high-efficiency furnaces available:
| Efficiency designation | Efficiency range (AFUE) |
| Low efficiency | 78-79% |
| Mid efficiency | 80-83% |
| High efficiency | 90-97% |
You'll notice that there's a gap between mid- and high-efficiency furnace efficiencies; that's because high efficiency furnaces use a different technology - so-called condensing furnaces condense water vapor out of the exhaust, and use the heat from this process, making them considerably more efficient than mid-efficiency furnaces.
You may find a furnace salesperson trying to sell you on a mid-efficiency furnace, on the argument that there really isn't that much difference between 83% AFUE and 90% AFUE. This has been my experience with most purchases of energy-consuming equipment: salespeople know it's easier to sell a cheaper, more wasteful appliance than a more expensive but more energy efficient one. People don't know how to do life-cycle cost projections, and the extra cost of an energy saving furnace can be considerable. For example, when I bought my 40,000 BTU high efficiency furnace in 1998 (six months after moving in), the price for that 94% efficient model was $2,800, while I could get a mid-efficiency furnace at 80% AFUE, from the same manufacturer, for just $1,500. Why spend the extra $1,300 for an extra 14% efficiency?
I even made a spreadsheet to calculate the payback period of the more energy saving furnace, and even assuming a 5% annual increase in natural gas prices, which at the time seemed quite high, gas prices having held pretty stable for the previous fifteen years, it would take at least 12 years to pay for itself. That's a pretty long payback period. But I went for the energy saving furnace anyway, because I knew the furnace would last longer than 12 years, and for a given amount of money I'd rather spend more of it creating jobs for furnace manufacturers and installers, and less of it sending CO2 into the atmosphere.
An extra bonus of an energy saving furnace in the high efficiency category, is that they use considerably less electricity than low- or mid-efficiency furnaces. They typically have more efficient and quieter DC motors, integrated circuit controls programmed to maximize efficiency, rather than mechanical thermostatic controls, and multiple-speed or continuously variant speed fan operation, which means they don't run the fan full blast unless there's major heating underway. A high efficiency furnace can use as little as one fifth as much electricity as a mid-efficiency furnace of the same BTU rating.
To see a more concrete example of how efficiency affects costs, take a look at the following table, which shows three different fuel efficiency scenarios for an energy saving furnace, and the lifetime energy costs of each, assuming the furnace lasts twenty years:
| Mid efficiency | High efficiency | Ultra high efficiency | |
| AFUE | 80% | 90% | 95% |
| Annual Natural Gas Cost | $750 | $660 | $635 |
| Annual Natural Electricity Use | 1,200 kWh | 990 kWh | 225 kWh |
| Annual Natural Electricity Cost | $96 | $80 | $18 |
| Lifetime Energy Cost | $11,730 | $10,230 | $9,030 |
| Lifetime Energy Cost Savings | - | $1,500 | $2,700 |
According to this estimate, by 2017 I should have saved just under $2,700 for my 94% efficient furnace over the 80% mid efficiency model I would have bought in 1997, minus the extra $1,200 I paid for a 94% efficient furnace instead of a mid-efficiency 80% model - that's a net savings of $1,500, or about two years worth of free heating out of the twenty-year expected lifetime. Put another way, my fuel savings each year are enough to cover the annual maintenance contract, which includes a cleaning, furnace adjustment, and a full warranty extension for an additional year. That's like getting a free 20-year warranty and service contract!
Exhaust venting
An energy saving furnace doesn't vent up your chimney. Because so much of the heat is extracted by a condensing gas furnace before the exhaust gases exit the home, the exhaust is instead vented through PVC pipes through an exterior wall. In fact, one of the key ways in which high efficiency furnaces save energy is that the use cold exterior air inside the sealed combustion chamber (as opposed to low- and mid-efficiency furnaces which suck warm air from inside your home into an open combustion chamber). This means that in a high efficiency furnace installation, you have two pipes connecting the furnace to the out of doors; the air intake pipe prevents the furnace from pulling cold air into the house from drafts around windows and doors as it burns up the oxygen.
One issue to cover with your HVAC contractor is where the air intake and exhaust pipes will be routed. Make sure the pipes are going where you want them to go, not where the HVAC contractor may find it easiest or most convenient. This is one thing our contractor didn't get quite right - they ran the pipes the entire length of the basement, and then through a crawl space to a back wall - when we would have preferred to have them vented out a side wall. But there are also building code rules about where the exhaust can be vented - for example, since the exhaust gases from burning natural gas are slightly corrosive, you have to be careful not to vent directly onto a neighbor's wall!
Buying an energy saving furnace
If you're considering buying an energy saving furnace I would recommend starting with a list of the most efficient furnaces in the BTU category you need. If we want to move our society towards sustainability, it's important that we favor the most efficient brands to reward those companies for their energy efficiency initiatives. Some of the brands with the highest efficiency ratings are:
- York International - energy saving furnaces with efficiency ratings up to 98.0% AFUE, the best in the industry
- Carrier - also makes the Bryant brand, both of which are excellent quality and include many high efficiency models up to 96.6% AFUE. The furnace I bought was in their Bryant Plus90i line, has performed very well without any problems, and has saved me buckets of money (my natural gas bills are typically $600-800 per year, which is pretty cheap for Toronto).
- Air-Ease makes energy saving furnaces in the 90-95% AFUE range
- Comfort Aire offers the Conquest 90 line of 90+% gas furnaces
- Lennox, one of the most popular brands, offers 90-95% efficiency furnaces
- Trane, which has a solid reputation for high-efficiency air conditioners, also makes high-efficiency gas furnaces (Brands XR95, XV95, XC95 and others)
For a complete list of energy saving furnace models and manufacturers, check the following websites:
- For the US, check the ENERGY STAR website and select Products > Heating and Cooling > Furnaces.
- For Canada, where the ENERGY STAR program also applies, check the above ENERGY STAR site or the Canadian Office of Energy Efficiency.
One thing to note is that the actual manufacturer of your furnace is often not the company whose brand name occurs on the product. Many of the most popular household appliance brands, such as Amana, American Standard, Frigidaire, Kenmore, Maytag, Tappan, Westinghouse, and Whirlpool, sell brands made by other manufacturers. For example:
- Frigidaire, Tappan, and Westinghouse all sell the FG6TE condensing gas furnace (95.1% AFUE)
- Frigidaire, Maytag, Tappan and Westinghouse all offer models with the exact same AFUE ratings and similar model number descriptions
What sets a Maytag model apart from the exact same furnace branded by Tappan? Your HVAC contractor may try to sell you one brand over another simply because they have more experience with that brand, or because that brand has spent more money marketing their product. If the unit is identical, don't worry about the brand.
There are definitely some brands that have built a solid reputation for reliability, but studies suggest that in over 80% of cases where unscheduled maintenance is required on a furnace or air conditioning system, at least part of the problem originated with a faulty installation, rather than with the quality of the brand purchased. The message here?
Find a top-notch HVAC contractor
If you're going to spend an extra $500 to $2,000 getting the most energy saving furnace you can buy, make sure you find an HVAC contractor with a solid reputation and who has experience installing the type of furnace you are looking for. Some tips on finding a good contractor:
- Company size or installation base: a company with thousands of satisfied customers is not going to risk their reputation doing a substandard installation. And companies don't get big by delivering bad quality. Ask for references, letters from previous customers, number of installations per year.
- Awards and reviews. The company I chose had won 'Readers Choice' awards, year after year, for being the best HVAC company according to readers of a local weekly community newspaper.
- Trust and professionalism: invite the salesperson to your home and check that they are professional, courteous, do not slam the competition (instead merely pointing out the superior quality of the brands they sell), and do not do a high pressure sales job on you.
- Knowledge of energy efficiency: If a salesperson tries to convince you that energy efficiency shouldn't be a major consideration, find another company. If they seem to know less than you do about the efficiency of their products, move on. You want someone who makes their living selling high-quality, energy saving furnaces, not someone who goes for large volume, low value sales. That's a recipe for quick and careless installation.
- Warranty and service contract: a company that offers at least a one-year warranty on the equipment and installation, including parts and labor, and whose annual service contract for the equipment you want to buy is affordable, offers the free warranty and affordable service contract because they know their installers will do a quality job up front, avoiding many of the unexpected maintenance calls that result from poor installation.
- Willingness to take on the whole job: your contractor should be willing to remove all equipment that is no longer needed, and dispose of it. They should provide a schedule for installation with a guarantee of one-day installation (where possible) and a promise to dispose of all unneeded equipment (including drainage and removal of any tank from an oil furnace) at no extra cost. For ducted installations (which applies to most furnaces) any sheet metal that needs to be custom fitted should be cut and installed the day the furnace goes in.
- Don't forget to ask friends and neighbors for references (and if they recommend a company, ask what their annual natural gas bill is!). The companies that grow their business through strong customer recommendations are probably doing a better job than those that rely on big Yellow Pages ads to bring in new customers.
Sizing your unit - how many BTU should your energy saving furnace be?
One of the things you'll need to ask your HVAC installer to do - and you should ask each company you invite into your home to do their own - is a capacity sizing for the new equipment. They need to tell you the BTU capacity of your furnace. Typical BTU ratings for home use are 40,000 BTU (works for our 1,300 square foot home in a cold Toronto climate) to 120,000 BTU (good for a monster home!).
A competent HVAC contractor will do a load calculation for your home based on a number of factors:
- Square footage of the home
- Ceiling height, since that plus square footage determines the volume of air to be heated
- Level of wall insulation and attic ceiling insulation
- Air-tightness of home
- Local climate
- Your preferred comfort temperature
Some contractors will do this calculation in their heads, others on paper with a calculator, while others will use specialized software to come up with the BTU capacity your furnace needs. Make sure to question them on what factors they considered in their load calculation, and watch out for a BTU rating that seems too high (for instance, higher than that provided by other HVAC contractors or than those of the furnaces of your neighbors).
An interesting aside - although my house of 1,300 square feet was sized by several HVAC contractors as needing a 60,000 BTU furnace, the company that eventually sold me my energy saving furnace suggested I go with the 40,000 BTU model, because it was 2% more efficient than their ultra high efficiency 60,000 BTU model and because they said there would be very few times when I'd need the full 60,000 BTU - namely extremely cold nights, of which we only get two or three a year.
In spite of some very cold Toronto winters and some barely insulated walls, we have never had trouble keeping the house warm, so when you get the HVAC contractors out to your house to do an estimate, pay close attention to what each estimator is telling you in terms of required BTU capacity. And don't forget that you are likely to increase the efficiency of your home over its lifetime, for example by upgrading insulation or adding energy efficient windows, so the need for a higher BTU energy saving furnace will decrease over time.
Don't forget the programmable thermostat
If you're going to the expense of installing an energy saving furnace, make sure the installation comes with a programmable thermostat. Many high efficiency furnaces require a specialized thermostat that comes as part of the installation. If yours doesn't, ask the installer to throw in a high quality programmable thermostat as part of the deal. There's no point in installing an energy saving furnace and not using a programmable thermostat, which lowers the heat when you're asleep or out of the house, and raises it when you're up and about inside. Programmable thermostats (also called set-back thermostats) can cut your energy bills by 10% or more, depending on how big a spread you set between the comfort and energy saving temperatures, and how much of the time you program the schedule to be in energy saving mode.
Filters and humidifiers
If you're going to the expense of buying a pricey but energy saving furnace, you'd be foolish not to consider the quality of the furnace filter and the importance of properly humidifying the air coming out of your forced air vents.
Furnace filters: You can buy inexpensive disposable furnace filters at most hardware stores or building supply stores. The furnace includes a slot about an inch wide; you slide the old filter out and slide the new one in. Such filters typically need to be replaced once a month while the furnace is active; if you have a pet that sheds, or a particularly dusty environment, the filter may need to be changed even more often.
A more convenient choice is a pleated filter that may only need to be changed every 6-12 months. For example, Aprilaire sells a range of whole house air cleaners that install as part of your furnace installation. The media for these filters is a pleated paper fabric, and the surface area through which the ductwork air passes catches much finer grained particles than a typical 1" thick filter. Although these filters are much more expensive, they last far longer and lead to improved energy efficiency, because they don't clog up as fast, and the more clogged up a furnace filter is, the more strain it puts on the furnace fan (and the less hot air the fan can push around).
Humidifiers: In cold weather - especially below freezing temperature - the outside air becomes drier, and this dryness translates into lowered indoor humidity levels. There are two problems with low indoor humidity in cold weather: the dryness can make you more prone to colds, as your airways are dehydrated and stressed, making it easier for microorganisms to gain a foothold, and, at the temperatures we typically heat our houses,air actually feels colder when dry than when humid. Increasing the relative humidity inside your heated spaces from 15% to 30%, while maintaining the same temperature, will actually help you feel quite a bit warmer.
You can buy a humidifier as part of your installation. This unit typically drips water over a metal mesh, and a portion of the ducted air blows through the mesh, picking up humidity and adding it into the air coming out of your heating ducts. A humidifier usually includes a dial to control the humidity level; the colder the outdoor weather, the more you'll need to compensate by increasing the indoor humidity. Since furnaces are typically installed in basements, where humidity problems are worth keeping an eye on, it's a good idea to put a hygrometer in a frequently used room in your basement; when the indoor humiditydips too low, you'll know it's time to increase the humidifier setting on the furnace.
Get ready for comfort
An energy saving furnace should allow you to enjoy comfortable temperatures without your spending a fortune on natural gas. By selecting a high efficiency model, a competent and experienced HVAC contractor, and the right additional options such as filtering equipment, humidifier, and programmable thermostat, you'll maximize the energy efficiency of your home heating while cutting your CO2 emissions and your energy costs.
Return from Energy saving furnace to Energy efficient home heating or to the Green Energy Efficient Homes site home page.
© Green Energy Efficient Homes 2010 Privacy policy | Disclaimers
