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Natural gas furnaces are common because they are dependable and familiar. To keep operating costs reasonable, you need to know how efficient the unit is, whether it is sized correctly, what a replacement costs today, and when an older furnace is no longer worth repairing.
AFUE means Annual Fuel Utilization Efficiency. It tells you what percent of the gas the furnace turns into heat in your home over a season. Older furnaces can be in the 70–80% range. Many current standard gas furnaces are around 80–90%. High-efficiency (condensing) gas furnaces reach roughly 90–98% because they pull extra heat from the exhaust. The U.S. Department of Energy has finalized a rule that will require most new residential gas furnaces to be at least 95% AFUE starting in late 2028, so older 80% units will be below that future minimum.
If your furnace is already high-efficiency and running well, keep it maintained. If it is an older 80% furnace, it is reasonable to price a replacement, so you know your options before the rule applies.
Furnaces are sold by BTU output. The right BTU number depends on house size, winter temperatures, insulation, windows, and ductwork. Many homes end up somewhere in the 60,000–100,000 BTU range, but the exact size should come from a load calculation, not a guess or “same as the old one.” A furnace that is too large will short cycle; one that is too small will run a long time and still struggle on cold days.
The 2025 guide you shared says a new furnace, including installation, ranges from 1,600 to 10,000 dollars with an average of about 4,800 dollars. Gas furnaces sit in the middle of that range, at about 3,800 to 10,000 dollars depending on size, efficiency, and labor. Higher AFUE units cost more at install but can save fuel over time, especially in colder areas. Final price still depends on location, duct or vent changes, and the BTU size the contractor specifies. Getting two quotes is the best way to confirm your number.
Check the furnace or HVAC filter every month during heating season and replace it if it looks gray, matted, or if airflow at the vents has dropped. Have a technician once a year clean and test burners, ignition, blower, venting, and safety controls. Keep supply and return grilles clear. Clean air across the heat exchanger is what lets the unit run close to its rated AFUE.
Most guidance says to start considering replacement when a furnace or boiler is more than 15 years old, especially if bills or repairs are increasing. If you are calling for service every season, or if a technician finds a heat-exchanger or venting issue on an old furnace, replacement is usually the better long-term choice. The coming 95% AFUE requirement in 2028 is another reason to plan if you still have an older 80% model.
A natural gas furnace needs a correctly sized, clean return filter to keep airflow and efficiency where the installer set them. A loose or overloaded filter can increase strain on the system and let dust reach internal parts.
Filterbuy offers pleated HVAC and furnace filters in MERV 8, MERV 11, and MERV 13 in both standard and custom sizes, made in the USA and shipped with free delivery. You can turn on Auto Delivery, so a replacement arrives on the same schedule as your monthly filter check.
AFUE (Annual Fuel Utilization Efficiency) is the percent of gas that becomes heat in your home over a season. Higher AFUE means less heat is wasted.
It can still run, but it uses more gas than newer high-efficiency models, and DOE is moving most new furnaces to 95% AFUE starting in late 2028, so it’s smart to plan ahead.
2025 pricing shows full installs in roughly the $1,600–$10,000 range, with gas furnaces commonly in the middle of that range depending on size, efficiency, and labor.
Ask the installer to do a load calculation. Do not guess and do not pick “the biggest.” Too big short cycles, too small struggles on cold days.
Look at it every month during the heating season and change it when it looks gray or airflow drops.
Yes. A quick annual check helps burners, ignition, venting, and safety devices work right and keeps efficiency closer to the rating.
If the furnace is 15–20 years old, if repairs are coming every winter, or if a tech finds a heat-exchanger or venting problem, replacement is usually better.
Higher AFUE wastes less gas, but actual savings depend on your climate, gas price, and how much the furnace runs.
Yes. A filter that is clogged or does not fit can reduce airflow and make the furnace work harder.
You can keep airflow and efficiency on track by using a snug, correctly sized pleated filter in MERV 8, 11, or 13 and replacing it on schedule. Filterbuy ships these in standard and custom sizes and you can set Auto Delivery so you always have a clean one.
