Furnace Installation in Herndon, VA
A new furnace here will run from October through April every year. Tell us about the house, and a licensed contractor who covers Fairfax County will get in touch.
Tell us about the job
It takes about a minute.
Herndon asks a furnace to run seven months of the year
From October through April your furnace is the thing standing between you and a 28°F night. That's the average low here in the coldest months, not the extreme, so the unit is cycling on and off for seven months straight. More than half the homes in the area heat with gas, which means most furnace installations here are gas furnaces sized to keep up with that long a season.
Any non-weatherized gas furnace built after November 2015 has to reach at least 80 percent AFUE by federal rule, so that's the floor for a new one, not a selling point. Power is the other thing worth planning around. Virginia saw 22 percent of households lose power for a full day or more in 2024, and the region has logged 387 damaging wind events and 10 winter storms over the past ten years. A new furnace should be installed with that in mind, since a furnace with no power is a furnace that can't light no matter how efficient it is.
- 7 months
- October through April, your furnace is on duty
- 28°F
- the average winter night it heats against
- 54%
- of homes here heat with gas, so most furnaces here burn gas
- 80% AFUE
- the federal minimum any new unit must meet
NOAA nClimDiv, 1991–2020 normals
A high-efficiency gas furnace would save about $100 a year to run in Fairfax County compared with a gas furnace.
Estimates for a typical Fairfax County home, from EIA household energy data, Virginia fuel prices and NOAA climate normals. Your home will differ.
Virginia requires HVAC contractors to hold a state license.
The license comes from the Board for Contractors, and it belongs to the contractor's business, not to any single job. It means the contractor was tested and is on record with the state. Work under $1,000 does not need a licensed contractor in Virginia, but a furnace installation runs well past that line.
The license tells you the contractor was tested. It does not tell you the furnace was installed correctly. That check comes from Fairfax County. In most cities and counties, a furnace replacement needs a permit from the local building office, and an inspector checks the work once it is done, including the gas connection and venting. More than half the homes in Fairfax County heat with gas, so that inspection is what catches a bad connection before it becomes dangerous.
Sources: Virginia General Assembly · Virginia Department of Professional and Occupational Regulation
- What size furnace does my house need?
- It depends on your home's square footage, insulation, window count, and layout, so there is no single number that fits every house. A contractor works this out with a load calculation, which looks at how much heat your home loses on a cold night, not just floor area. Guessing high seems safe but it isn't. A furnace too large for the house cycles on and off fast, which wears out parts sooner and leaves rooms uneven. With winter lows here averaging 28°F and heat needed October through April, getting the size right matters more than it would in a milder climate.
- How do I know it's time to replace my furnace?
- Watch for a few signs together, not just one. Rooms that used to heat evenly now have cold spots, the furnace cycles on and off more than it used to, or you are calling for repairs more than once a season. Age matters too, especially in a place where the furnace runs 7 months of the year. If yours is older and something just failed, that is usually the point where replacing makes more sense than repairing again. A contractor can look at the specific unit and tell you which side of that line it's on.
- Is a high-efficiency furnace worth it?
- Any non-weatherized gas furnace sold new has to reach at least 80 percent AFUE, so even a standard model wastes less fuel than an older one. A high-efficiency furnace goes beyond that minimum, so more of the gas you pay for turns into heat in the house rather than going out the flue. Over half of homes in this area heat with gas, and the season here runs October through April, so that difference gets used often. Whether the higher upfront cost is worth it for your house depends on how long you plan to stay in it and what your current furnace is costing you to run, and a contractor can walk through those numbers for your specific home.