# HVAC load and equipment sizing

> 2000 sq ft, furnace + AC: a rough heat loss of 37,200 BTU/h and heat gain of 26,100 BTU/h, a cross-check before the room-by-room Manual J. For HVAC pros: a rough load by area and climate zone, equipment size, ducts, registers and line sets.

## What to buy (2000 sq ft, furnace + AC)

Every line shows the quantity to buy and how StudSheet got it: the spacing, the waste and the package size, so you can check it before the supply house or the quote.

| Buy | Material | How StudSheet counts it | What it is for |
|---|---|---|---|
| **1 furnace** | Gas furnace, 40,000–45,000 BTU/h (40,000 BTU/h input, 95%+ AFUE) | Output ≈ 38,000 BTU/h (95% of input) for the 37,200 BTU/h heat loss: 102%. | Condensing (95%+ AFUE) furnace, vented with plastic pipe. Input rating; the output is about 95% of it. |
| **1 unit** | AC condensing unit, 2.5–3 ton (2.5 ton, A2L (R-454B or R-32)) | 26,100 BTU/h heat gain ÷ 12,000 = 2.17 tons → 2.5 tons. | Outdoor half of a split central air conditioner. A2L refrigerant (R-454B or R-32) on units made since 2025. |
| **1 coil** | Evaporator coil, up to 3 ton (2.5 ton, matched to the condenser) | An AHRI-matched coil and condenser pair is what the efficiency rating (and many rebates) count. | Cased A-coil that sits on the furnace and matches the condenser (AHRI-matched pair). |
| **1 set** | Line set (insulated copper pair) (3/8 × 3/4 × 35′) | Coil to outdoor unit about 32 ft (across to the wall, out, to the unit, service loops). Factory charge covers about 15 ft: add about 10 oz (the R-410A figure; A2L units list theirs on the data plate). The unit’s instructions set the sizes. | Liquid and suction lines from the coil to the outdoor unit, suction insulated. Sized by the unit’s installation instructions. |
| **1 drier** | Liquid-line filter drier (liquid line) | If the outdoor unit doesn’t ship with one. | Catches moisture and debris; bi-flow for heat pumps. |
| **1 pack** | Brazing rods, 15% silver | Line set joints, brazed with nitrogen flowing. | For copper-to-copper and copper-to-brass joints, brazed with nitrogen flowing. |
| **6 sections** | Rectangular trunk duct (10×20 × 5′) | 27 ft of extended plenum along the house, sized for 1,000 CFM at about 800 ft/min. | Sheet-metal supply trunk (extended plenum) in 5 ft sections, from a supplier or your shop. |
| **2 caps** | Trunk end cap (10×20) | Both ends of the trunk. | Closes the far end of a rectangular trunk. |
| **1 plenum** | Supply plenum | On the coil or air handler, feeding the trunk. | Box on top of the coil or furnace outlet that feeds the trunk. |
| **1 plenum** | Return plenum or return drop | Into the furnace or air handler, with the filter. | Feeds return air into the furnace or air handler; filter rack included on most. |
| **14 take-offs** | Round take-off with damper | 14 supply runs: the dampers balance the rooms. | Starting collar that connects a branch run to the trunk or plenum; the damper balances the run. |
| **5 collars** | Round start collar | 5 return runs into the return plenum: no damper on a return. | Plain collar (no damper) that connects a return run to the return plenum or trunk. |
| **13 bags** | Insulated flex duct, 4–10 inch (6″ R-6 × 25′) | 14 runs of about 21 ft (294 ft + 5%) in 25 ft bags; 70 CFM each is a 6″ run at about 0.1 in. w.c. per 100 ft. | Sold in 25 ft bags. R-8 in attics, R-6 elsewhere outside the heated space. Pull it tight and support it every 4–5 ft. |
| **5 bags** | Insulated flex duct, 4–10 inch (8″ R-6 × 25′) | 3 bedroom returns, 102 ft in all. | Sold in 25 ft bags. R-8 in attics, R-6 elsewhere outside the heated space. Pull it tight and support it every 4–5 ft. |
| **2 bags** | Insulated flex duct, 12–16 inch (12″ R-6 × 25′) | 2 central returns of 500 CFM, 37 ft to the return plenum (or panned joists and a sheet-metal drop instead). | Sold in 25 ft bags, for return runs. R-8 in attics, R-6 elsewhere outside the heated space. |
| **14 boots** | Register boot (4×10 × 6″) | One per supply. | Box at the end of a run that holds the register: 4×10 with a 6-inch collar, for example. |
| **14 registers** | Supply register (4×10) | About one per 150 sq ft of floor, each about 70 CFM. | Steel floor, wall or ceiling register with a damper. |
| **2 grilles** | Filter return grille (20×20) | One central return per floor, each about 500 CFM through a 1-inch filter. | Central return grille that holds a 1-inch filter. |
| **3 grilles** | Return grille (10×10) | One per bedroom (4 people → 3 bedrooms), so closed doors don’t starve the room — or a jumper duct. | Bedroom return or jumper grille, so a closed door doesn’t choke the room. |
| **4 gallons** | Duct mastic (1 gal) | About 85 joints and seams, 25 to a gallon. | Water-based sealant brushed over every joint and seam (UL 181 listed). |
| **2 rolls** | UL 181 foil tape | Holds joints while the mastic cures; never cloth duct tape. | Foil tape listed for ducts — not cloth duct tape. |
| **1 pack** | Flex duct clamps (pack) (packs of 50) | Inner liner and jacket at both ends of every flex run. | Nylon draw bands that lock flex duct onto collars and boots (UL 181B-C). |
| **2 rolls** | Duct hanger strap (100 ft) (100′ roll) | Supports every 4–5 ft, without pinching the duct. | Wide strap that carries flex and trunks without pinching them. |
| **15 ft** | Condensate line (3/4 PVC) | About 15 ft from the coil and the furnace to a drain or the pump. | Plastic tubing or small PVC from the condensate outlet to a drain or pump. |
| **1 kit** | Condensate fittings | A trap, a tee with a cleanout and the elbows. | Trap, tee with cleanout, elbows, primer and cement. |
| **1 pump** | Condensate pump | Unless a floor drain is within reach. | Lifts condensate to a drain when there’s no floor drain nearby. |
| **38 ft** | PVC DWV pipe, 2 in (2″ Schedule 40 PVC, solid core) | Vent and combustion-air pipes, about 19 ft each to the side wall. The furnace’s venting table sets the size and the longest run; no cellular-core pipe. | Schedule 40 PVC drain, waste and vent pipe. |
| **1 kit** | Vent termination kit (2″ concentric or two-pipe) | The furnace maker’s listed termination, with its clearances to windows, doors and the gas meter. | Wall or roof termination for power-vent, direct-vent or tankless venting, as the maker lists it. |
| **1 kit** | Vent fittings | Long-sweep elbows, couplings, hangers, primer and cement. | Long-sweep elbows, couplings, hangers, primer and cement. |
| **1 valve** | Gas appliance shutoff valve | Shutoff in the same room as the furnace. | Listed gas ball valve in the same room as the appliance (the gas fitter picks the size). |
| **1 kit** | Sediment trap and union | Drip leg and union at the furnace; the gas fitter sizes and pressure-tests the piping. | Black-iron tee, nipple and cap (drip leg) and a ground-joint union at the furnace. The gas fitter sizes and tests the piping. |
| **2 alarms** | Carbon monoxide alarm | One on each floor outside the sleeping areas: codes ask for them when a fuel-burning appliance goes in. Ask whether they must be hardwired. | Outside the sleeping areas when a fuel-burning appliance goes in. Ask whether it must be hardwired. |
| **1 switch** | Furnace service switch | Service switch at the furnace (on its own circuit). | On-off switch at the furnace or air handler, in a box. |
| **1 pad** | Equipment pad | Level and a few inches above the ground (typical code wording: 3″). Confirm with your building department. | Composite or concrete pad that keeps the outdoor unit level and off the ground. |
| **1 set** | Locking refrigerant caps (set) | Codes ask for tamper-resistant caps on refrigerant ports outdoors. | Tamper-resistant caps for the service ports outdoors. |
| **1 refill** | Dry nitrogen refill | Purge while brazing, then the pressure test before the vacuum. | For purging while brazing and the pressure test before the vacuum. |
| **1 disconnect** | AC disconnect, non-fused (60 A, fused if the nameplate says so) | Within sight of the outdoor unit (NEC 440.14). | Pull-out disconnect within sight of the condenser (NEC 440.14); fused when the nameplate asks for fuses. |
| **1 whip** | AC whip, ¾-inch liquidtight, 6 ft | Disconnect to unit. | Pre-made flexible connection from the disconnect to the condenser; conductors sized for the unit. |
| **1 breaker** | Breaker, 2-pole (per the nameplate MOP) | Enter the nameplate MCA and MOP to size it. | 240 V breaker listed for your panel; takes two spaces. |
| **48 ft** | NM cable 10/2 with ground (10/2 with ground, typical — size it from the MCA) | Panel to disconnect, about 48 ft — a guess: the panel’s place sets it. Cable inside; the electrician picks UF, conduit or a whip outside. | NM-B (NMD90 in Canada): 30 A 240 V circuits with no neutral — water heaters, some EV chargers. |
| **1 thermostat** | Thermostat (heat and cool) | One per system, on an inside wall away from supply registers and sun. | Programmable or smart; heat-pump models handle the backup heat stage. |
| **29 ft** | Thermostat wire (18/5) | Equipment to thermostat, with a spare conductor or two and a C wire. | 18-gauge solid, by the conductor count (18/5, 18/8). |
| **37 ft** | Thermostat wire (18/2) | Along the line set to the outdoor unit. | 18-gauge solid, by the conductor count (18/5, 18/8). |

### In Canada (185.8 m², furnace + AC)

Set to Canada, the Sheet works the job out again for Ontario: metric sizes, bag sizes, the frost depth and the code notes. It doesn't just convert feet to meters. The first lines:

- **1 furnace, Gas furnace, 60,000–70,000 BTU/h:** Output ≈ 57,000 BTU/h (16.7 kW) (95% of input) for the 45,900 BTU/h (13.5 kW) heat loss: 124%.
- **1 unit, AC condensing unit, 1.5–2 ton:** 23,600 BTU/h (6.9 kW) heat gain ÷ 12,000 = 1.97 tons → 2 tons (7 kW).
- **1 coil, Evaporator coil, up to 3 ton:** An AHRI-matched coil and condenser pair is what the efficiency rating (and many rebates) count.
- **1 set, Line set (insulated copper pair):** Coil to outdoor unit about 9.75 m (across to the wall, out, to the unit, service loops). Factory charge covers about 4.57 m: add about 283 g (the R-410A figure; A2L units list theirs on the data plate). The unit’s instructions set the sizes.
- **1 drier, Liquid-line filter drier:** If the outdoor unit doesn’t ship with one.
- **1 pack, Brazing rods, 15% silver:** Line set joints, brazed with nitrogen flowing.

## The order of work, for the licensed pro

> **PRO JOB: a licensed contractor’s job. The order of work is here so you know what’s involved and what to ask.** About 34–50 hours of work for this example.

1. Walk the house: measure the floors and windows, note the insulation and air sealing, and pick the spots for the equipment, trunk and returns and the outdoor unit.
2. Run the room-by-room load calculation (ACCA Manual J) with your county’s design temperatures — this Sheet’s number is only a cross-check.
3. Select the equipment with Manual S (extended performance data at your design conditions) and lay out the ducts with Manual D.
4. Pull the permits (mechanical, gas and electrical) and attach the calculations where the office asks for them.
5. Set the furnace and coil level on the return plenum with its service clearances, and the outdoor unit on its pad.
6. Run the trunk, take-offs and branch runs to the boots; seal every joint with mastic, pull flex tight and support it every 4–5 ft, and insulate what runs outside the heated space.
7. Vent the furnace by its venting table; the gas fitter connects the gas, with a sediment trap and a shutoff, and pressure-tests the piping.
8. Braze the line set with nitrogen flowing, then pressure-test it with nitrogen.
9. Evacuate to 500 microns or lower and prove it holds with the pump valved off, then open the service valves.
10. Electrician: the outdoor unit’s circuit and a disconnect within sight of it, the furnace’s own circuit and service switch, and the low-voltage wiring.
11. Rough-in inspection: ducts and venting, the gas piping test — before ceilings, walls or the attic close.
12. Start up: weigh in the charge for the line length, check superheat or subcooling, measure the static pressure and temperature rise against the nameplate, set the gas pressure and check combustion and CO, and test every mode.
13. Test the duct leakage where the energy code asks (ducts outside the heated space); balance the registers.
14. Label the system (refrigerant, charge, installer), leave the manuals at the unit, show the owner the thermostat and filters, and book the final inspection.

## Tools (31)

Must-have tools first, then the ones that help and the ones to rent for the day.

| Tool | Need | Why |
|---|---|---|
| **Tape measure (25 ft)** | **Must have** | The red boxes every 16″ on the blade are stud spacing. |
| **4-ft level** | **Must have** | Equipment and pad level, so condensate drains |
| **Cordless drill/driver** | **Must have** | Drills holes, drives screws, mixes small batches. |
| **Impact driver** | **Must have** | Drives long framing and deck screws without stripping. |
| **Aviation snips** | **Must have** | Sheet metal, collars and take-off holes |
| **Oscillating multi-tool** | **Must have** | Boot openings in floors and ceilings |
| **Utility knife + blades** | **Must have** | Cuts flex duct and its insulation |
| **Cut-resistant gloves** | **Must have** | Sheet-metal edges cut deep |
| **Digital manifold gauges** | **Must have** | Pressures and temperatures to charge by superheat or subcooling |
| **Vacuum pump** | **Must have** | A2L-rated: evacuate the lines and coil |
| **Micron gauge** | **Must have** | Proves the vacuum reaches 500 microns and holds |
| **Refrigerant scale** | **Must have** | Weighs in the extra charge for the line length |
| **Nitrogen regulator + tank** | **Must have** | Flows nitrogen while brazing; pressure-tests the lines |
| **Tubing cutter** | **Must have** | Wheel cutter that makes square, burr-free cuts in copper tubing. |
| **Deburring tool** | **Must have** | Cleans the cut edge of pipe inside and out so fittings seal and flow isn’t blocked. |
| **Oxy-acetylene torch kit** | **Must have** | Brazing the line set (or an air-acetylene torch) |
| **Heat shield (welding blanket)** | **Must have** | Protects framing and siding behind the joints |
| **Refrigerant leak detector** | Good to have | An A2L-capable sniffer for the final check |
| **Combustion analyzer** | **Must have** | CO and combustion at start-up |
| **Gas leak detector** | **Must have** | Every gas joint the job touched |
| **Digital manometer** | **Must have** | Gas pressure and the duct system’s static pressure |
| **Digital multimeter** | **Must have** | Voltage and controls at start-up |
| **Clamp meter** | **Must have** | Compressor and blower amps against the nameplate |
| **Lockout/tagout kit** | **Must have** | Breakers off and locked while you work |
| **Blower door + duct tester** | Rent | Duct leakage test where the energy code asks for one |
| **Air balancing hood** | Good to have | Balances the registers to the design airflows |
| **Appliance dolly** | **Must have** | Furnaces, air handlers and outdoor units down stairs and over lawns |
| **Step ladder (6 ft)** | **Must have** | Reaches 8-ft ceilings safely. |
| **Safety glasses** | **Must have** | Every cut, every nail, every time. |
| **Work gloves** | **Must have** | Fiberglass, sheet-metal edges and cold refrigerant at the hoses |
| **N95 dust masks** | **Must have** | Fiberglass in flex jackets, attics and old ductwork |

## Mistakes and how the math works

### Mistakes that cost a callback or a second trip

- **Sizing by the square foot:** Rules like 500 sq ft a ton oversize most houses: short cycles, clammy air, cold and hot rooms. Run the load, room by room.
- **Starving the return:** One small return chokes the blower: high static pressure, noise, and a frozen coil or an overheated heat exchanger. Size returns for the full airflow.
- **Sagging, kinked flex:** Every sag and sharp bend cuts the airflow. Pull flex tight, support it every 4–5 ft, and keep runs short.
- **A short vacuum:** Air and moisture left in the lines break down the oil and kill the compressor. Pull below 500 microns and prove it holds before opening the valves.
- **Treating A2L like R-410A:** R-454B and R-32 are mildly flammable: A2L-rated recovery machine and vacuum pump, no open flame near a charged system, and the label the code asks for.
- **Venting by habit:** Each furnace’s venting table sets the pipe size, the longest run and the elbows; terminations keep their clearances to windows, doors and the gas meter.

### What the calculator assumes

- Block load: 2000 sq ft on 2 floors, 8′ ceilings, R-13 walls, R-30 attic, double-pane windows, 0.5 air changes an hour. Heat loss = (envelope 449 BTU/h·°F + air leakage 144 BTU/h·°F) × 57°F (70°F inside, 13°F outside) × 1.1 for ducts in the basement = 37,200 BTU/h. Heat gain = walls, ceiling and glass at 17°F over 75°F (plus sun on walls and a hot attic), sun through 300 sq ft of glass 9,000 BTU/h, appliances 2,000 BTU/h, 4 people 900 BTU/h, × 1.05 for the ducts = 23,400 BTU/h sensible + 2,700 BTU/h latent (people and humid air).
- Footprint 1000 sq ft a floor as a 1.5 : 1 rectangle (39′ × 26′); glass 15% of the floor area; 2 doors. Indoors 70°F in winter, 75°F in summer.
- Heat pump output in the cold, as a share of its rating at 47°F: standard about 62% at 17°F and 48% at 5°F; cold-climate about 90% and 78% (NEEP asks at least 70% at 5°F). The unit’s extended data decides.
- Airflow 400 CFM a ton, or the furnace’s output at a 60°F rise when that’s more. Flex at about 0.1 in. w.c. per 100 ft: 5-inch 50 CFM, 6-inch 100, 7-inch 150, 8-inch 200, 14-inch 800. One supply per 150 sq ft; a central return on each floor (a filter grille carries about 800 CFM); a return or jumper in each bedroom, counting people − 1 bedrooms.
- Runs measured on the drawing’s layout: along the outside walls from a trunk down the middle, plus the climb between floors and 3 ft for the boot. Manual D sets the real sizes and routes.
- Line sets (typical; the unit’s instructions decide): up to 3 tons 3/8 × 3/4, 3.5–5 tons 3/8 × 7/8. Factory charge for 15 ft of line.
- Prices are typical US contractor prices (fall 2026); equipment by size class.

## Code, permits and safety

The Sheet sets its code notes for the job's state or province. These are New Jersey's and Ontario's; the [code reference](https://studsheet.com/codes) has more. Always confirm with your building department.

- **Rough estimate, not a Manual J:** A whole-house block load from typical U-values and design temperatures: good for a sanity check and a first price, never for sizing. Size the equipment from a room-by-room ACCA Manual J (loads), Manual S (equipment) and Manual D (ducts): IRC M1401.3 and M1601.1 call for them, and many permit offices ask to see them — Pima County and Phoenix in Arizona, Alachua County in Florida even for change-outs, California (CALGreen 4.507.2) for new homes.
- **Pick your climate zone:** Figured for zone 4 (13°F winter and 92°F summer) until you pick one under Climate zone. New Jersey is zone 4A, except Bergen, Hunterdon, Morris, Passaic, Somerset, Sussex and Warren counties (zone 5A, NJ DCA Bulletin 22-1); zone 5 makes the heat loss 44,400 BTU/h.
- **Equipment:** Cooling: 2.5 tons for a 26,100 BTU/h heat gain (115%; Manual S asks 95–115% for single-stage). Heat: a 40,000 BTU/h input furnace (about 38,000 BTU/h output at 95%, 102% of the 37,200 BTU/h heat loss; Manual S: 100–140%). Pick a cabinet whose blower moves 1,000 CFM for the AC. Airflow: 1,000 CFM.
- **Refrigerant rules:** Only EPA Section 608 certified technicians (Type II or Universal for these systems) may open the circuit and buy refrigerant. New split systems since 2025 use A2L (R-454B or R-32), mildly flammable: equipment listed to UL 60335-2-40, A2L-rated recovery machine and vacuum pump, no ignition sources near the work, the refrigerant and charge on the label (2024 IRC M1411). R-410A equipment made before 2025 may still be installed (EPA’s 2026 rule), unless your state set its own deadline — New York did. Gas: a licensed gas fitter or plumber (or the HVACR licensee) connects and tests the gas piping.
- **Permits: mechanical, gas and electrical:** In New Jersey a licensed master HVACR contractor pulls the permits from your town’s construction office: HVACR work is limited to licensees, except a homeowner on their own home (N.J.A.C. 5:23-2.15). Gas piping goes with the HVACR or the master plumber license. The outdoor unit’s circuit goes under the electrical subcode. Plan for rough and final inspections.
- **Enter the nameplate MCA and MOP:** The outdoor unit’s breaker and wire come from its nameplate: enter its MCA (minimum circuit ampacity) and MOP (maximum fuse or breaker) above. A disconnect goes within sight of the unit (NEC 440.14).
- **Rough estimate, not a CSA F280 calculation:** A whole-house block load from typical U-values and design temperatures: good for a sanity check and a first price, never for sizing. In Canada the heat loss and gain come from a room-by-room CSA F280 calculation — the method the building codes point to (BC’s code requires it) — and permit offices ask for it with the drawings.
- **Design temperatures:** Ontario: figured with Toronto’s design temperatures, −18°C winter and 31°C summer (NBC Appendix C). Colder places in the province change the load a lot: use your municipality’s values in the F280.
- **Refrigerant, gas and licences:** Handling refrigerant takes Ontario’s Ozone Depletion Prevention (ODP) card (O. Reg. 463/10). New equipment uses A2L (R-454B or R-32), mildly flammable: equipment listed to CSA C22.2 No. 60335-2-40, A2L-rated recovery machine and vacuum pump, no ignition sources near the work, the charge on the label. Gas: a TSSA-registered contractor, with certified gas technicians (a G2 covers house appliances); plastic venting certified to ULC S636.
- **Permit likely needed:** New or replacement heating and cooling equipment and duct changes usually need a building permit from your municipality — Toronto lists furnace replacements, adding an air conditioner and duct alterations, and asks for heat loss and gain calculations, a duct design and ventilation calculations by a qualified designer. Gas work by a TSSA-registered contractor. The outdoor unit’s circuit by a licensed electrician (ESA notification). Confirm with your building department.

## Questions

### What materials do I need to size a furnace and AC?

For the worked example, a 2000 sq ft, furnace + AC, the Sheet counts 43 lines with waste included, starting with gas furnace, 40,000–45,000 BTU/h (1 furnace), aC condensing unit, 2.5–3 ton (1 unit), evaporator coil, up to 3 ton (1 coil), line set (insulated copper pair) (1 set). Each line's math is in the table above. Put in your own sizes in the [hvac calculator](https://app.studsheet.com/p/hvac) and every line is counted again.

### How long does it take to size a furnace and AC, and can I do it myself?

About 34 to 50 hours for the worked example, in 14 steps. StudSheet stamps it **PRO JOB**: hire this out (pros get the full Sheet).

### What tools do I need to size a furnace and AC?

31 in all. The must-haves start with tape measure (25 ft), 4-ft level, cordless drill/driver, impact driver, aviation snips, oscillating multi-tool. On the Sheet you mark each one as owned, to buy or to rent.

## Ask about it

Stuck while you size a furnace and AC? Ask in the [Heating and cooling group](https://studsheet.com/forum/heating-and-cooling) of the StudSheet community with this Sheet attached. Homeowners who've done it and verified pros answer, and anyone can read it.

## More hvac Sheets

- **[HVAC for contractors](https://studsheet.com/trades/hvac)**: run this takeoff at your own prices, send the estimate, and get it signed and the deposit paid.
- **[All 45 Sheets](https://studsheet.com/sheets)**, across 16 trades.
- **[Code reference](https://studsheet.com/codes):** frost depths, guard heights, stairs, retaining walls.