low, high and mid efficiency Furnaces

New high-efficiency furnaces cost on average $1,000 to $3,000 more than low-efficient furnaces (installation included). That's significant, but easy to recover in fuel savings. But what about the alternative high vs. mid-efficiency furnaces?

AFUE - Annual Fuel Utilization Efficiency
The AFUE is a percentage expressing how much fuel the furnace converts into heat: say, 90% or 80%. A furnace with a AFUE of 75% is a low-efficient unit. A unit with an AFUE of 97% is a very high-efficient furnace. Most modern furnaces have AFUEs between 80% and 97%.
The AFUE rating is obviously important. But be aware. The performance of a furnace can be ruined by a poor installation. A well installed mid-efficiency furnace can outperform a poor installed high-efficiency furnace.

Older furnaces have an AFUE (Annual Fuel Utilization Efficiency) rating of 65% or less, a cause of high levels of energy loss and pollution. In fact, a low value (say 65%) indicates that a significant part of the fuel used by the furnace isn't converted into heat (35%).

A high AFUE (say 95%), on the contrary, indicates that only a small part of the fuel is lost and not converted into heat (5%).

DEFINITION
Low-efficiency furnaces: AFUE of 80% or less;
Mid-efficiency furnaces: AFUE of 80-89%;
High-efficiency furnaces (condensing furnaces): AFUE of 90% or more...

Low vs. High-Efficiency Furnaces

Suppose a low-efficiency gas furnace with a 70% AFUE (Annual Fuel Utilization Efficiency). Suppose that it costs you $2,000 installed while an high-efficiency 95% AFUE unit costs $4,000.

That's a significant difference of price, but relative to a 95% AFUE your energy bills will be at least 25% higher, which is also a lot.

Bottom line: it's easy to pay the extra-cost of a high-efficiency furnace. The payback period depends on your bills, but periods of 2 to 4 years are common. Low-efficient furnaces are a wrong option, economically and environmentally.

Prices Of Mid and High Efficiency Furnaces

But what about the alternative mid vs. high efficiency units?

Suppose that a 90% AFUE furnace is priced at $1,000 ($3,000 installed) while a sophisticated new 98% multi-stage furnace is priced at $2,000 ($5,000 installed).

Does the high-efficiency furnace deserves its extra-price? Or it makes only sense for energy conservation and because of the prospects of energy prices and the lifespan of furnaces?

It depends a lot on your energy bills... In cold climates, in homes with large energy bills, the answer is obviously yes. But in moderate climates (where there are good alternatives to furnaces) and for moderate heating needs it may not make economic sense.

If the energy savings of an high efficient furnace relative to a mid- or low-efficient are, say, $200 or more per year, the extra-cost of a high efficient furnace will be paid in 5 years or less … But if the savings are only $100 a year, or less, the payback period can be too large… Ultimately all depends also on your climate, your energy bills, or issues like rebates…

Alternatives to high efficient furnaces in moderate climates

Some specialists say that low-efficient furnaces can be a good choice for milder climates, and that the energy bills provided by high-efficiency furnaces do not offset their higher cost.

But it may also be argued that if the energy bills and the heating needs are small or relatively small, then it is also difficult to justify the use of a central furnace… In that case, high insulation levels and advanced windows combined with space heating strategies can replace with advantage a furnace-based system…

See: Alternatives to furnaces