The short answer
The expensive mistakes when replacing a furnace or AC in Northern Virginia happen before anyone picks up a wrench: waiting until it dies, copying the size off the old unit, comparing quotes by brand and bottom line, and ignoring the ducts. None of that takes any money to get right. It takes an hour and a few questions. Here’s what we’d tell a neighbor before they sign.
Before you pick anybody
Don’t wait for the coldest night. When it dies in January you take whoever’s open and whatever’s on the truck. If it’s near the end (here is how long a furnace lasts), start looking while it still runs. And don’t take a single sentence as the verdict. Repair or replace is a real decision, and a cracked heat exchanger is worth seeing with your own eyes. Ask for the photo.
Don’t call just one company. Two or three is enough. Here’s how to choose a contractor without reading reviews until your eyes cross.
Free Furnace With a New AC
Put in a new AC with its matching coil and a basic single-stage gas furnace goes in with it, installed together. See the free furnace
Want your own number before anyone comes out? The HVAC estimator prices your house in a few questions.
During the visit
Swipe to see all columns →
Swipe to see all columns →
| Don’t | Why | Ask this instead |
|---|---|---|
| Size it off the old unit | The old one may have been wrong on day one, and you may have added insulation or windows since. | “Are you doing a load calculation on my house?” The Air Conditioning Contractors of America publishes the method, called Manual J. |
| Buy the top efficiency number first | It won’t deliver through leaky ducts. | “What do my ducts look like, and how much am I losing?” |
| Replace only the outdoor half without asking | Mismatched parts can miss their rating or run poorly. | “Is this a matched system, and can you show me the rating?” |
| Let someone skip the walk-through | A number from the driveway is a guess. | “Can you look at the furnace, the ducts and the thermostat first?” |
| Skip the rooms that bother you | A new system won’t fix a room the ducts never reached. | “Here’s the room that’s always cold. What would fix it?” |
The sizing part matters more than people think. What size furnace you need and what size AC you need both come down to your house, and square footage alone is only a start. If one room is the whole complaint, zoning or a ductless unit may be what fixes it. Leaky ducts are worth finding before you pay for capacity that never reaches the bedroom.
When you’re holding the quotes
Don’t compare the bottom numbers first. Line them up side by side using how to read an HVAC quote. Check what’s in and what’s out:
- Permit and inspection
- Thermostat, pad, line set and drain work
- Haul-away of the old equipment
- Duct changes, if any
- Labor warranty, in writing, and who answers the phone for it
Check real numbers against our furnace and AC prices and what a new furnace costs here. Heat pump or gas? Here are both run side by side. And don’t sign because of a rebate somebody said on the phone. Here is where the tax credit stands, so check it before you count on it.
After it’s in
- Don’t skip the warranty registration. Many makers require it within a set number of days of install to give you the longer parts coverage. Ask who’s doing it, and get the confirmation.
- Don’t skip the county inspection. It’s a second set of eyes you already paid for with the permit, and it matters when you sell.
- Don’t forget the filter. New systems need it as much as old ones. Here is which one to buy, and it isn’t the highest MERV on the shelf.
- Don’t treat it like the old one. Here is what not to do to your furnace and to a heat pump.
Questions people ask
Should I replace my furnace and AC at the same time?
If both are near the end, usually yes, because they work as a matched system and you pay for one install. If one is fairly new, it’s worth asking whether it can stay. Have the tech show you both labels and explain it.
Is a bigger furnace better?
No. An oversized system heats the house fast, shuts off and starts again, which is hard on the parts and leaves uneven rooms. Size should come from a load calculation on your house.
How many quotes should I get for a new HVAC system?
Two or three is plenty. Past that you’re comparing noise. Line them up by what’s included, not just the bottom number.
Do I need a permit to replace a furnace or AC?
In Northern Virginia, a system replacement generally needs a mechanical permit. Your contractor should pull it and the county inspects the work. If someone offers to skip it, that’s your answer about them.
Book it
Not sure if it’s time? Have someone look before you decide, and get the photo either way. The heating check is $67 per system through December 31, on a furnace, heat pump or boiler. Book it from goswiftpro.com/cookiesoffer and free MOLTN cookies come with the visit. Or call (703) 997-9757. SwiftPro is rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
