Upgrading a traditional furnace to a new variable speed and multi-stage furnace can reduce your heating bills. Upgrading a 70% AFUE furnace to a 95% AFUE gas furnace can decrease your heating bills by 25%.
But it also depends on factors like the quality of the installation, the location, design and insulation of the ducts, and the levels of insulation and air sealing of your home.
And this raises a critical question: Which are the alternatives to central heating systems, and more specifically to furnace systems?See our videos on Furnaces here:
Buying Efficient Furnaces
Alternative 1: a small system in a super-Insulated home
You may have a properly sized, maintained and installed furnace, with a properly insulated and designed ductwork, but if you lose a large part of the heat through leakage paths in the home’s shell, or through the wall and attic materials, you will continue to have large energy bills.
Ideally, before upgrading your existing furnace, you should improve the levels of air sealing and insulation of your house. That’s very important to allow a smaller furnace and to properly size the ducts (ducts are often undersized, and leaky and poorly insulated, and a major cause of heating loss, especially when installed in attics, basements and garages).
If possible, before upgrading to a new furnace, look for gaps and holes in your home’s boundary and seal them; also insulate your walls, ceilings and floors to higher than common levels (see: Insulation for low energy homes), and consider replacing old inefficient windows.
Only then it will be advantageous to install a new - and smaller – furnace. Possibly, if your house isn't too large and the climate isn't too harsh, central furnaces can be replaced by new wall gas ductless furnaces or other type of space heaters. That’s not uncommon and that’s the goal of air-tight homes massively insulated.
That’s what we can call the “supper-insulation approach”, of which the German Passive House standards is a good example (you don't have to implement the strict standards of this type of homes, but you will need very high levels of insulation and air-tightness all over the home's envelope, and high-energy-efficient windows, and to pay attention to details).
Since heat loss, in these buildings, is reduced to very low levels, you will not need central gas furnaces, or other sophisticated heating system.
Alternative 2: Boilers
Hydronic heating (involving boilers and baseboards, radiators or radiant floor heating) is a common alternative to furnaces, in many regions.
Unfortunately, though they provide high-quality heating, they have the same disadvantages of furnaces, from an energy standpoint. They are even more expensive to run than furnaces, and they are expensive to buy and install, especially radiant floor heating.
Alternative 3: Heat pumps
Heat pumps are another alternative to furnaces.
Geothermal heat pumps, a special heater with a large ground coil system - are expensive to install, and only make sense for very large energy requirements.
Small heat pumps systems (especiallyt ductless heat-pumps/mini-splits) combined with super-insulation and air-tightness are an excellent option, even in cold climates; new cold-climate heat pumps can be effective even at temperatures as low as -13ºF/-25ºC.
Alternative 4: Other types of furnaces
Central gas furnaces have several alternatives within the furnace family. But these other choices aren't really advantageous, except perhaps gas wall furnaces when combined with super-insulation in moderate climates, in very air-tight homes.
In this case, a couple of ductless wall furnaces can be a good alternative to central heating systems. Many super-insulated homes rely on ductless furnaces, or other equivalent heating systems.
The other types of furnaces – oil furnaces, electric furnaces or even pellet furnaces – are not affordable or advantageous enough. Electric furnaces involve high running costs, oil furnaces haven’t any significant advantage over gas furnaces, and sophisticated pellet furnaces require a high investment and are mostly intended to large heating requirements.
See: Types of Furnaces