Sizing, Manual J and what a good quote must include
The right size comes from a calculation, not square feet. Use the checklist to compare quotes line by line.
- Last checked: November 8, 2026
- Sources: ACCA, DOE, Mass Save
Last checked November 8, 2026
At a glance
The short version. Ask every contractor for the Manual J heating-load calculation and the equipment model. Then compare the same scope across quotes. A quote with no load calculation is a guess.
What a Manual J load calculation is
ACCA's Manual J is the national standard for working out how much heat a house loses and gains. The U.S. Department of Energy describes the three ACCA manuals this way: Manual J estimates the heat loss and heat gain of the structure, Manual S guides equipment selection from those loads, and Manual D sizes the ducts (DOE Building America).
- Manual J, the loadWalls, windows, insulation, air leaks, orientation and the outdoor design temperature set how many BTU per hour the house loses on the coldest design day.
- Manual S, the equipmentPick a unit whose output fits that load, not one that is simply bigger.
- Manual D, the ductsFor ducted systems, size the ducts so the air actually gets to the rooms.
DOE: "In the past, many HVAC contractors used rules of thumb to determine HVAC sizing and, as a result, many installed oversized systems. Today's trained HVAC contractor should determine your heating and cooling loads, and the right size for your HVAC equipment, based on calculations developed by the Air Conditioning Contractors of America." A new furnace, DOE adds, "may be more efficient but is still likely to be oversized."
How big is big enough
Published sizing windows, as a percent of the heating load
100% means the equipment output equals the calculated load at the outdoor design temperature.
Mass Save partial-home sizing bonus90 to 120% of load
Cold-climate heat pump, no backup heat100 to 115%
Cold-climate heat pump with supplemental heat75 to 85%
Furnace (Manual S limit)up to 140%
The DOE cold-climate guide warns that "grossly oversizing equipment, whether individual zones or a whole house, can lead to excessive cycling, low efficiency and ineffective summer dehumidification," and says to use full ACCA Manual J or equivalent. For a heat pump, Mass Save also says: "Heat pumps perform best when a home is sufficiently weatherized and the system is sized properly for the home."
Tons, for the rebate
Mass Save's rebate counts tons as AHRI cooling capacity divided by 12,000 BTU. That is a rebate rule, not a sizing rule. If you have a quote in BTU per hour, turn it into tons and a rebate.
What the code says
The model 2021 International Energy Conservation Code, section R403.7, reads: "Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies. New or replacement heating and cooling equipment shall have an efficiency rating equal to or greater than the minimum required by federal law for the geographic location where the equipment is installed." Massachusetts's base code is IECC 2021 with Massachusetts amendments (780 CMR Chapter 11R). We read the model text, not the amendments, so ask your building department how a replacement is treated.
The quote checklist
The quote checklist: ten things every written quote needs
Print it and tick each line against every quote you get.
- The heating-load calculationA copy of the Manual J, or the contractor's plan to run one. One of Mass Save's questions to ask an installer is whether they plan to perform a heat load calculation to size the system. It is required for the heat pump sizing bonus.
- Equipment make, model and efficiencyFor a furnace or boiler, the model and its AFUE. For a heat pump, indoor and outdoor model numbers, the AHRI certified reference number and the ENERGY STAR Cold Climate listing Mass Save requires.
- Full scope in plain wordsRemoval and disposal of the old unit, venting or chimney work, gas line, oil line and tank, ducts or piping, thermostat, condensate, and any electrical work or panel upgrade.
- Which permits, and who pulls themGas fitting, oil burner, sheet metal and electrical permits are separate. See permits and inspections. Mass.gov's contract language says a registered contractor agrees to pull the building permit and any other necessary permits.
- Licence numbers you can checkThe plumber or gas fitter, the oil burner technician and the electrician. Look each up (table below). Do not assume a company name is a licence.
- DatesThe start and completion dates of the project, and for a 2026 Mass Save heat pump rebate, an install date before December 31, 2026 in writing.
- A payment schedule in dollarsWith the date and amount of each payment. On a home improvement contract a deposit cannot exceed one-third of the contract price, and final payment cannot be demanded until the contract is completed to the satisfaction of all parties.
- The warranty, attachedMass.gov's sample contract asks whether an express warranty is provided and says all terms must be attached. Ask who stands behind the labor and who stands behind the equipment.
- Rebate and paperwork dutiesWho files the Mass Save form, and that the invoice will carry what Mass Save requires: installer name and address, model numbers, installation date and address, total install cost per system, proof of payment and the serial-number nameplate photo.
- Cancellation and change termsA contract signed away from the contractor's place of business can be cancelled in writing by midnight of the third business day after signing, per Mass.gov's sample language. Ask how changes in scope are priced.
From the Aurion guide at aurionelectric.com, last checked November 8, 2026.
Quote scorecard
| Line | Quote A | Quote B | Quote C |
|---|---|---|---|
| Manual J provided | Yes / No | Yes / No | Yes / No |
| Model numbers and efficiency | |||
| Old unit removed | |||
| Venting, lines, tank, electrical | |||
| Permits listed, who pulls | |||
| Licence numbers checked | |||
| Start and finish dates | |||
| Payment schedule, deposit | |||
| Warranty attached | |||
| Total price |
Check the licences
| Work | Where to check |
|---|---|
| Plumbers, gas fitters, electricians, construction supervisors | Division of Occupational Licensure, check a license |
| Oil burner technicians | Department of Fire Services license lookup. The certificate allows the holder to service, install and repair oil burners. |
| Pipefitters and refrigeration technicians | Office of Public Safety and Inspections license verification |
| Home improvement contractor registration, where it applies | MA Contractor Hub |
Mass.gov: not all home improvement work requires a HIC registration; installers of central heating and air conditioning, and licensed plumbers and electricians working within their trade, are listed as not needing one. A registered contractor must agree to arbitrate, and the Guaranty Fund compensates eligible homeowners up to $25,000 for unpaid judgments. We did not find which state licence a heat pump refrigerant circuit needs, so ask the contractor to name the licence holder and check it on the lookup above. HIC homeowner resources, HIC program.
Red flags
- No load calculation, or "we size by square feet."
- A price with no model numbers.
- A deposit above one-third of a home improvement contract.
- "No permit needed." Ask for the permit number and the inspector's sign-off.
- Pressure to sign the same day, or a heat pump quote that does not say whether the contractor is in the Mass Save Heat Pump Installer Network.
Where Aurion takes the project
Aurion takes the project from your photos to a written quote with the scope above, runs the permits and rebate paperwork, and has licensed Massachusetts technicians do the licensed work. Send a photo of the old unit and one of the panel. Related: what drives a boiler price, boiler and furnace replacement.
Common questions
What is a Manual J load calculation?
A room-by-room calculation of how much heat your house loses, using the procedure in the ACCA Manual J standard. ACCA calls Manual J 8th Edition the national ANSI-recognized standard for producing HVAC equipment sizing loads for single-family detached homes, small multi-unit structures, condominiums and townhouses.
Can a contractor size my furnace or boiler by square footage?
The U.S. Department of Energy says that in the past many contractors used rules of thumb and installed oversized systems, and that today a trained contractor should determine your heating and cooling loads using the calculations developed by ACCA. Square feet alone cannot tell a tight house from a drafty one.
Is a bigger furnace or boiler better?
No. DOE says a newer furnace may be more efficient but is still likely to be oversized, and its building science guidance warns that grossly oversizing equipment can lead to excessive cycling, low efficiency and poor summer dehumidification.
How big can a furnace be compared with the load?
ACCA Manual S, as summarized in DOE's strategy guideline, recommends that furnace size stay within 140% of the peak heating load estimate.
How big should a cold-climate heat pump be?
DOE's 2024 guide for cold-climate air-source heat pumps says to match system capacity at the design temperature to 100 to 115% of the estimated heating load without auxiliary heat, or design for 75 to 85% of the load and include just enough supplemental heat. It also says to use full ACCA Manual J or equivalent.
What does Mass Save require for sizing?
For the $500 partial-home sizing bonus, equipment must be sized to meet 90 to 120% of the total heating load at the outdoor design temperature, per ACCA Manual J, throughout 100% of the conditioned space, and a copy of the heating load calculation must be submitted with the application. For the rebate itself, tons are AHRI cooling capacity divided by 12,000 BTU.
Does Massachusetts require a load calculation for a replacement?
The model 2021 International Energy Conservation Code, section R403.7, says heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved methods. Massachusetts's base code is IECC 2021 with state amendments. We did not verify how the Massachusetts amendments treat a like-for-like swap, so ask your building department.
Do I need a home improvement contractor registration for a furnace or boiler job?
Mass.gov lists installers of central heating and air conditioning, and licensed plumbers and electricians working within their licensed trade, among work that does not require a home improvement contractor (HIC) registration. That means the HIC arbitration and Guaranty Fund protections may not apply to a pure HVAC job, so check the trade licences instead.
How much can a contractor ask for up front?
For home improvement contracts, a deposit cannot exceed one-third of the total contract price, except for special-order or custom materials that must be ordered before the work starts. Mass.gov also says home improvement contracts over $1,000 must be in writing.
Questions? Call (781) 210-8400 or send two photos and your town.
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