How to Compare Furnace Replacement Quotes

Three quotes for the same job arrive with three different numbers and almost no way to tell why. That is the normal experience of buying a furnace, and it is not because the equipment costs wildly different amounts. It is because a furnace installation is mostly labor and materials around the furnace — venting, gas, condensate, ductwork, controls, disposal — and quotes vary enormously in how much of that they actually include. Compare the scope and the prices start making sense.

Was the furnace sized from a load calculation?

Ask every contractor how they arrived at the size, and listen for whether they calculated it or copied it. A load calculation measures the house — square footage by area, insulation levels, window type and area, air leakage, orientation and the local design temperature — and produces the heating load in BTUs. Copying the old furnace's nameplate repeats whatever decision someone made decades ago, which in older Northland houses was often generous by a wide margin.

Oversizing has real consequences. An oversized furnace satisfies the thermostat quickly and shuts off, so it short-cycles, the house gets uneven temperatures, and the equipment never settles into steady operation. It also matters more now than it used to, because houses here have been insulated, air-sealed and re-windowed over the years, and a house that needed a large furnace in 1985 frequently does not need one today. If a quote arrived without anyone measuring windows or asking about insulation, the size on it is an inheritance rather than a calculation.

What should be itemized on a furnace quote?

A furnace quote should itemize everything that will happen at your house, not just the model number of the equipment. Use this as a checklist and ask about any line that is missing — missing usually means either not needed or not included, and those are very different things.

• Equipment: model number, AFUE, single-stage or two-stage or modulating, and the blower type.
• Venting: new PVC intake and exhaust for a condensing furnace, or flue and liner work for an 80% AFUE unit, including where the terminations will go.
• Condensate: trap, drain routing, any pump, and how the line is protected from freezing.
• Gas piping: whether the existing line is adequate for the new furnace's input, and any piping changes.
• Electrical: disconnect, circuit, and any wiring changes the new equipment requires.
• Ductwork: return sizing, plenum transitions, filter cabinet, and any modifications needed to move the required air.
• Thermostat: the specific model, and whether it matches the furnace's staging.
• Permit and inspection, stated explicitly rather than assumed.
• Removal and disposal of the old furnace, and of any old tank or equipment being retired.
• Startup and commissioning, with the readings provided in writing.
• Warranty: parts term, labor term, and who registers the equipment.

The questions that separate one quote from another

A handful of questions reveal more about a furnace quote than the total does. They are all fair to ask, and the answers are things a contractor should be comfortable putting in writing.

What to ask, and what a clear answer sounds like

Question	A clear answer	Worth pressing on
How did you size it?	A load calculation, with the inputs described	"Same as what is there now"
Where will the vents terminate?	A specific wall and height, chosen for snow and wind	Unspecified, or "wherever the old ones were"
Is the return duct big enough?	A measured static pressure or a stated plan to enlarge it	The subject is not raised at all
Is the permit included?	Yes, with the fee shown	Vague, or left to the homeowner
What readings will I get at startup?	Gas pressure, temperature rise, static pressure, combustion	"We make sure it runs"
What is the labor warranty?	A stated term, separate from the parts warranty	Only the manufacturer's parts coverage is mentioned

Does the quote address the water heater?

If your old furnace shared a chimney with a natural gas or propane water heater, replacing it with a condensing furnace leaves that water heater alone on a chimney sized for two appliances — and this has to be addressed in the quote. A single water heater often cannot produce enough draft to carry its flue gas up an oversized, cold masonry chimney. The flue gas condenses, the chimney deteriorates, and in the worst case combustion gas spills back into the house.

This is a common situation in the older housing stock across the region, and it has a name and a proper set of remedies, explained in the orphaned water heater chimney risk. What matters at quote time is simply that it appears. A quote that relines the chimney, or replaces the water heater with a sidewall-vented or electric unit, is not more expensive than one that ignores the problem — it is a different scope.

Commissioning: the part that is rarely in writing

Commissioning is the set of measurements taken after the furnace is installed to prove it is running the way it was designed to, and it is the most commonly skipped part of a furnace installation. A new furnace out of the box is not automatically set up for your house. Manifold gas pressure has to be checked and adjusted for the fuel and the altitude, blower speed has to be set so temperature rise lands inside the rating plate range, static pressure has to be measured to confirm the ducts can move that air, and combustion analysis has to confirm a clean burn through the venting as installed.

Ask for those four readings in writing on the invoice. They take a technician additional time on site, which is part of why quotes differ, and they are the difference between a furnace that is installed and a furnace that is commissioned. They also become the baseline every future service visit compares against. If a duct system will not let the furnace hit its numbers, that is a finding worth having on day one, since it usually points at ductwork and airflow work rather than at the furnace.

Warranty, rebates and the paperwork nobody mentions

Parts warranty and labor warranty are two different things, and a quote should state both. Manufacturer parts coverage comes with the equipment and usually depends on registration within a set window after installation — ask who does that, because an unregistered furnace can fall back to a shorter term. Labor coverage comes from the installing contractor and varies a great deal. Many manufacturers also expect documented annual maintenance, a point covered in whether skipping maintenance voids a furnace warranty.

Rebates are their own paperwork. Depending on where you live and what you burn, a high-efficiency furnace may qualify through Comfort Systems (Duluth city gas) rebates, Minnesota Energy Resources rebates elsewhere in Minnesota, or Focus on Energy in Wisconsin — and a household in South Range is looking at a different program list than one in Canosia. Amounts and eligibility change, so we confirm current figures at quote time; the rebate landscape across Minnesota and Wisconsin covers how the programs differ. Ask each contractor who fills out which forms.

How do you compare furnace quotes step by step?

1. Confirm each contractor sized the furnace from a load calculation.
2. Line up the itemized scope: equipment, venting, condensate, gas, electrical, ducts, thermostat.
3. Check where the vent terminations go and how the condensate line is kept from freezing.
4. Confirm the quote deals with a water heater left on the old chimney.
5. Ask for commissioning readings in writing on the invoice.
6. Compare parts and labor warranty terms and rebate paperwork.
7. Only then compare the prices.

How should you weigh price against everything else?

Once the scopes match, compare the prices — and by then the comparison is usually straightforward. Furnace replacement in this area generally falls in the $4,500–$9,500 range, with the spread driven by the equipment tier, the venting work, whether gas piping or electrical has to change, and how much duct modification the house needs. A quote well under that range is normally missing scope, and a quote above it usually includes work the others left out.

Two things are worth more than a few hundred dollars of difference in a −17°F to −21°F climate: the equipment being sized for the house, and the installation being commissioned with readings you can hold. Those decide whether the furnace runs quietly for many winters or becomes a repeat service call. Whether the house is in town or out past Pike Lake, the quote worth accepting is the one that describes the whole job — and it is entirely reasonable to ask for a furnace replacement quote itemized that way before you decide.