What to Ask Before You Sign for a Furnace or Heat Pump

The moment to pay attention is when the tablet comes out at your kitchen table and swivels toward you with three options on it. Good, better, best. Silver, gold, platinum. The cheap one has a sad little icon next to it and the expensive one has a badge that says "Most Popular."

That screen is a sales tool, not an engineering document. The actual decision was made twenty minutes earlier, when the guy either did or didn't measure your house, count your windows and put a gauge on your ductwork. Everything after that's trim.

So ask the three questions that sort the pros from the closers, and ask them before anybody prices anything.

Question one: where's the Manual J?

Manual J is the load calculation. It's the industry-standard math for how much heating and cooling your specific house needs, based on square footage, insulation, window area and orientation, air leakage, ceiling height and your climate zone. A contractor who does one will happily print it. A contractor who doesn't will tell you he's been doing this thirty years and he can size a house by looking at it.

Maybe he can. But the old rule of thumb, a ton of cooling per 400 or 500 square feet, was built for leaky houses with single-pane windows, and if you've replaced windows, added attic insulation or air-sealed anything, your house needs less equipment than it did in 1994.

Oversizing is the most common and most expensive mistake in residential HVAC, and it's the one that gets sold to you as a favor. Bigger unit, more comfort, right? No. An oversized furnace blasts, satisfies the thermostat in six minutes and shuts off, then does it again. You get hot-cold swings, drafts off the registers and a heat exchanger that lives its whole life in the hardest part of its cycle. An oversized air conditioner or heat pump is worse in summer, because it cools the air fast without running long enough to pull moisture out. Then your house is 72 degrees and clammy, and you buy a dehumidifier to fix a problem you paid extra to create.

Ask for the load calc. If the result comes back suspiciously close to whatever's in your basement now, ask why. Replacing like-for-like is a default, not an answer.

Question two: what's my static pressure?

This is the question that changes the room. Static pressure is the resistance your duct system puts on the blower, measured in inches of water column. Most residential equipment is designed around roughly 0.5 in. w.c. total external static. A lot of real houses are running well north of that, because somebody added a thick filter, or the return is one undersized grille in a hallway, or the flex duct has a kink in it behind the furnace.

Here's what that costs you: on a choked duct system, a brand-new high-efficiency system will underperform a properly installed basic one. The blower can't move the air it was designed to move. Rooms at the end of the run stay cold. A variable-speed blower will ramp up to compensate and you'll hear it doing it.

A tech who carries a manometer and takes a reading is telling you he cares about the outcome. A tech who's never mentioned your ducts is selling you a box.

If the number is high, fixing the return air or replacing a crushed run is real money and it's worth every dollar, more than any efficiency tier upgrade on the tablet.

Question three: what are the model numbers, and is it an AHRI-matched system?

Get the outdoor unit model, the indoor coil model and the furnace or air handler model in writing on every quote. Same for the AHRI reference number. Without it, you're comparing "gold package" to "premium system" and you'll pick based on the salesman you liked more.

With model numbers, three quotes become a real comparison. You'll also catch the classic trick: matching a new high-efficiency outdoor unit to your existing indoor coil. It's cheaper, it's sometimes defensible, and it usually means you don't get the rated efficiency you're paying for.

Furnace, heat pump, or both

The honest answer depends on what you pay for gas and what you pay for electricity, and those are local numbers you can pull off your own bills tonight.

A cold-climate heat pump is genuinely good technology now. The thing to check isn't the SEER2 or HSPF2 rating on the brochure. It's the capacity table: how many BTUs does this unit actually produce at 5 degrees, or at whatever your design temperature is? Capacity falls as it gets colder. If the unit makes 36,000 BTUs at 47 degrees and 21,000 at 5 degrees, and your house needs 40,000 on the coldest night, the difference comes from backup heat.

Electric resistance backup works fine and costs a fortune to run. That's why dual fuel exists: heat pump does the mild weather, gas furnace takes over below a changeover point you set. In a place with cheap natural gas and real winters, that's often the smart buy, and it's also the one that costs the most up front because you're purchasing two heating systems.

If your gas furnace is 12 years old, working, and vented properly, there's no shame in keeping it and putting the money into insulation and air sealing instead. Equipment you don't need is the most expensive equipment there is.

The upsells to decline, and the ones to pay for

Decline, usually:

• UV lights and air "purifiers" bolted into the plenum. Big margin, thin benefit for most homes.
• Extended labor warranties past the first few years. You're insuring against a bad installation. Hire someone who won't do one.
• The maintenance membership signed the same night. Buy it later, if the company earns it.
• Efficiency tiers you can't justify with math. Ask what the annual dollar savings is between the two units, then divide the price difference by it. If the payback runs past the equipment's life, it's jewelry.

Pay for, gladly:

• Duct and return-air corrections identified by an actual measurement.
• A permit and a municipal inspection. If a contractor suggests skipping it to save you money, he's saving himself a second opinion.
• A 4-inch media filter cabinet if your setup allows it. Better filtration, lower resistance, one change every six months instead of four.
• Proper commissioning: refrigerant weighed in, airflow verified, combustion analyzed on gas equipment, numbers written on the invoice.
• A condensate overflow safety switch if the air handler sits in an attic over finished ceilings.

The part where you stay out of it

Replacing a furnace or heat pump isn't a Saturday project. Gas piping, combustion venting, 240-volt circuits, refrigerant handling that legally requires EPA certification. Carbon monoxide doesn't announce itself. This is a licensed-contractor job, full stop, and a permit and inspection are cheap insurance against somebody's shortcut.

What's yours: change the filter on schedule, keep two feet clear around the outdoor unit, pour a cup of distilled vinegar down the condensate line in spring, register the warranty within the manufacturer's window, and stop closing vents in unused rooms. That last one raises static pressure and you now know why that matters.

And do this in September, not on the coldest night of the year with a dead furnace and one company answering the phone. Emergency is the highest-margin word in the trade.