How long should I wait after changing the filter before my AC starts cooling again?

Give the system 20–30 minutes after changing a severely clogged filter. If the evaporator coil froze due to restricted airflow, you may need to let it thaw for 2–4 hours with the system in fan-only mode before full cooling returns.

My AC runs constantly but can't reach the thermostat setpoint on hot days. Is that normal in Fairfax?

On extreme heat days, it's normal for a correctly sized AC to run nearly continuously. If it's running non-stop on a moderate summer day and still can't catch up, you likely have an airflow problem, a refrigerant issue, or a system sizing problem.

Should I turn my AC off if it's not cooling, or keep running it?

If you suspect a frozen coil, switch to fan-only mode or turn the system off. For other issues like a dirty filter or dirty condenser, you can continue running while you address the fix. When uncertain, fan-only is the safest setting.

How do I verify an HVAC contractor is licensed in Virginia?

Virginia requires all HVAC contractors to hold an active license through the Virginia Department of Professional and Occupational Regulation (DPOR). You can verify any contractor's license status on their website.

Is a heat pump a good replacement for a failing AC in Northern Virginia?

Yes — modern variable-speed heat pumps are well-suited to NoVA's Climate Zone 4A. They qualify for the largest federal tax credits available in 2026 and Dominion Energy offers rebates for qualifying installations.

Back to BlogHome Buying · Fairfax, VA · Northern Virginia

Buying an Older Home in Fairfax County? What to Know About Its HVAC History

Older Fairfax County homes can hide expensive HVAC surprises. What to investigate before closing, from equipment age and service records to refrigerant type, warranty status, ductwork condition, and combustion safety, plus a printable pre-purchase checklist.

October 13, 2026 By the Fairfax Mechanical Team 9 min read

Short answer: When buying an older Fairfax County home, investigate the age of the HVAC equipment, available service records, any past renovations that affected the system, the status of warranties, and the refrigerant type, then budget accordingly. The goal is to know what you are inheriting before closing, not after the first breakdown. Fairfax Mechanical is an experienced, licensed Virginia HVAC contractor that performs pre-purchase HVAC assessments for Northern Virginia homebuyers, so you walk into closing knowing exactly what the system is worth and what it will need.

Buying an older home in Fairfax County? Check its HVAC history

Older homes in Fairfax County have character, mature neighborhoods, and often great value, but their HVAC systems can hold expensive surprises. Before you close, doing your due diligence on the heating and cooling history protects you from inheriting a failing or unsafe system.

Why HVAC history matters in an older home

HVAC is one of the most expensive systems in a home to repair or replace, and in an older Fairfax County home, it may be near or past the end of its life. A furnace lasts about 15 to 20 years, and an AC or heat pump about 15. If the equipment is that old, a replacement could be in your near future.

Knowing this before closing lets you negotiate, budget, or walk away with your eyes open.

What to investigate before closing

✓
Equipment installation datesFind the age of the furnace, AC, and heat pump, usually on a label or data plate. Age tells you how much service life remains.
✓
Service and maintenance recordsAsk the seller for the maintenance history. A well-documented, regularly tuned-up system is far more reliable than one with no records. Gaps suggest neglect.
✓
Past renovationsOlder homes often have additions or finished basements. Ask whether the HVAC was properly extended or upsized for those changes, or whether rooms were simply tacked onto an undersized system, a common source of comfort complaints.
✓
Refrigerant typeOlder AC systems may use R-22, long phased out, or R-410A, now being phased down in favor of R-454B. An older-refrigerant system can mean costly repairs down the road.
✓
Warranty statusFind out whether any equipment is still under a manufacturer warranty, and whether it transfers to you.
✓
The ductworkIn older homes, aging ductwork can leak 20 to 30 percent of conditioned air. Ask about its condition.
✓
SafetyFor gas furnaces and boilers, a cracked heat exchanger is a carbon monoxide risk. A pre-purchase inspection should check this.

The printable home-buying HVAC checklist

✓
Age of furnace, AC, or heat pump
✓
Maintenance and service records
✓
Refrigerant type (R-22, R-410A, or R-454B)
✓
Warranty status and transferability
✓
Past additions or renovations, and whether the HVAC was properly extended
✓
Ductwork condition and leakage
✓
Thermostat type and age
✓
Combustion safety (heat exchanger, venting, carbon monoxide)
✓
Overall system condition and remaining life estimate
✓
Budget for near-term repair or replacement

Why a pre-purchase HVAC assessment pays off

A standard home inspection gives HVAC a cursory look. A dedicated pre-purchase HVAC assessment tells you the real condition, remaining life, and likely costs, information you can use to negotiate or plan. On a major purchase, it is inexpensive insurance.

Do this before your inspection contingency expires

Schedule the HVAC assessment early in your due diligence window. If it surfaces a system at the end of its life, you still have time to negotiate, ask for a credit, or adjust your budget.

Why choose Fairfax Mechanical

We are an experienced, licensed Virginia HVAC contractor, and we perform thorough pre-purchase HVAC assessments for Fairfax County and Northern Virginia homebuyers, so you know exactly what you are inheriting before you close.

“A furnace that is nineteen years old is not a dealbreaker. Not knowing that it is nineteen years old is.”Fairfax Mechanical Technical Team, Fairfax, VA

Buying a home in Fairfax County? Get the HVAC assessed first.

Get My Free Estimate

Frequently Asked Questions

How do I find out how old the HVAC equipment is?

Look for the data plate or label on the furnace, air conditioner, or heat pump. It usually lists a manufacture date or a serial number you can decode. Age tells you how much service life remains on a system that typically lasts 15 to 20 years.

Does a home inspection cover the HVAC system?

A standard home inspection gives the HVAC a cursory look. It is not the same as a dedicated pre-purchase HVAC assessment that measures refrigerant pressures, electrical draw, and combustion safety, and estimates remaining life.

Why does refrigerant type matter when buying an older home?

Older AC systems may use R-22, which has been phased out, or R-410A, which is now being phased down in favor of R-454B. An older-refrigerant system can mean more expensive repairs down the road, so it belongs in your budget planning.

Should I ask for HVAC service records?

Yes. A well-documented, regularly tuned-up system is far more reliable than one with no records. Gaps in the history suggest neglect, and that is worth knowing before you close.

Why choose Fairfax Mechanical for a pre-purchase assessment?

Need help with your AC?

Free estimate for any HVAC service in Northern Virginia.

Get My Free Estimate →