Like a lot of Northern Virginia, a Herndon address covers two jurisdictions. The incorporated Town of Herndon runs its own government around the old Washington and Old Dominion railroad depot. The rest of 20170 and nearly all of 20171, the part built out for the Dulles corridor, is Fairfax County. That decides who inspects a furnace replacement, and any contractor quoting you should know which one you are in.
What it does not change is the equipment. Herndon is furnace and heat pump country. We essentially never work on a boiler here, which puts it in the same bracket as Reston and Sterling and a world away from Falls Church.
Two housing stocks, two failure patterns
The old town blocks. Smaller, older houses near the depot and along the trail, where heating was fitted in long after the house was built. Tight mechanical spaces, ducts threaded where they would go, and frequently a ductless head in a converted attic or an addition. The constraint here is almost always access rather than the equipment.
The corridor build-out. Single family homes, townhouses and condos that went up through the 1980s and 1990s as the technology corridor filled in. Gas furnaces with central air, sealed combustion on the later ones, two systems in the larger houses, and heat pumps across a good share of the townhouses and condos. This is most of our Herndon work, and that equipment is now between twenty and thirty five years old.
That age is the whole story. A furnace built in 1994 has had a good run, and the parts that fail at this stage are predictable.
What goes wrong at twenty five years
It lights, runs a few seconds, shuts off, retries. Flame sensor. $95 to $180 to clean, and our most common no-heat call anywhere.
Clicking with no flame. Hot surface igniter, $240 to $410. Ceramic gets brittle with age and finally cracks.
Runs ten or fifteen minutes and shuts down. Overheating on restricted airflow. The filter first, then the blower wheel at $300 to $440 to pull and clean.
A squeal or grind from the blower. Blower motor, $670 to $2,400 depending on standard or variable speed. If it still runs, do not wait for it to seize in January when the part takes a weekend to source.
A whine or rattle before the burners light. The inducer motor. When it fails the furnace will not light at all. About $1,950, and a genuine decision point on a thirty year old furnace.
Water near a high efficiency furnace, or one that will not start. Condensate trap, $175 to $420.
Heat pump iced over and staying that way. Frost on a damp 35 degree day is normal. A block of ice at noon is not, and it is usually the defrost board at $450 to $1,150. Switch to Emergency Heat and call before the ice takes the fan blades.
Typical Repair Costs for Furnaces and Heating Systems
- Diagnostic visit: about $99.
- Flame sensor cleaned $95 to $180; igniter or sensor replaced $240 to $410.
- Condensate drain or trap $175 to $420. Thermostat $300 to $640.
- Blower wheel cleaned $300 to $440. Blower motor $670 to $2,400.
- Control board $550 to $1,180. Inducer motor about $1,950.
- Heat pump defrost board $450 to $1,150. Capacitor $240 to $370.
Full furnace list here; heat pump version here.
When a thirty year old furnace stops being worth fixing
ASHRAE puts a gas furnace’s median service life at eighteen years. Plenty run longer, and we are happy to keep one going when the repair is small. The line we use is simple: past fifteen years, if the repair is more than a third of a replacement, replace it. A $1,950 inducer on a 1994 furnace is most of the way to a new one with the rest of the furnace still thirty years old.
A furnace alone runs $4,498 to $12,300 installed; a furnace and air conditioner together $8,898 to $23,000 by system size. If the air conditioner went in the same year, doing both at once beats two jobs two years apart, because the labor and the permit overlap. Washington Gas is paying $500 to $700 toward a high efficiency furnace through its contractor network this cycle.
The estimator gives you the installed range for your size in about two minutes with no phone number.
October list
Run the heat for an hour now. Stand by the furnace for the first two minutes and listen for inducer, igniter, burners, blower, in that order, no hesitation. Change the filter. Clear leaves from around and under the outdoor unit if you have a heat pump, because it drains defrost water out the bottom and a unit sitting in wet leaves freezes itself to the pad by February.
And put a carbon monoxide alarm on each sleeping floor. Virginia requires them in new construction with fuel burning appliances and has no retrofit rule, and the alarms that were installed in the 1990s are long past their service life.
SwiftPro repairs heating systems across Herndon, in the town and the county. Call (703) 997-9757, book online, or start at the Fairfax County heating repair page.
