Printable HVAC Heating Loss Worksheet

Measure the opaque exterior wall area after subtracting doors and glazing. Enter glazing and doors separately in the window/door row, and use an area-weighted U-factor if their properties differ. Counting a window in both rows is the easiest way to overstate the load.

Use whole-assembly U-factors. They account for framing and other construction paths, which carry heat around the insulation. The R-value printed on a batt or board is not the whole-wall R-value, so entering it directly understates the loss. Enter actual roof and wall areas rather than a floor-area multiplier.

Choose winter design temperatures and a defensible outdoor-air rate. Each loss row is shown separately so you can review which surface or airflow dominates. Print or save as PDF with the browser control and keep the inputs and assumptions with the results. Floors, ducts and adjacent-space losses are not included.

The 1.08 comes from 60 min/h × 0.075 lb/ft³ × 0.24 BTU/(lb·°F) and assumes standard air near sea level. At high elevation the air is less dense, so use a corrected factor. Convert BTU/h to watts by dividing by 3.412, and to tons of heat-pump capacity by dividing by 12,000.

The temperature difference is 70 − 20 = 50°F. Wall loss is 1,200 × 0.08 × 50 = 4,800 BTU/h; roof loss is 1,000 × 0.03 × 50 = 1,500 BTU/h; windows and doors lose 200 × 0.3 × 50 = 3,000 BTU/h; outdoor air costs 1.08 × 100 × 50 = 5,400 BTU/h. The heating loss subtotal is 14,700 BTU/h. Defaults are example assumptions, not universal design conditions.

Notice that outdoor air is the largest single row (about 37% of the total), larger than the walls. That is typical of a well-insulated house, where the envelope is already doing its job and the air path is what is left.

The table runs the same formulas on five stand-alone examples. All use 1,200 sq ft of net wall, 1,000 sq ft of roof and 200 sq ft of windows and doors. They are illustrations of how the inputs move the result, not benchmarks for any real home.

Two points stand out. Moving from the older envelope to the high-performance one cuts the load by about 70% at the same temperature, a much larger swing than any small area tweak. And the same house loses almost three times as much heat in the cold climate as in the mild one, which is why the design temperature matters as much as the insulation.

For orientation when choosing U-factors, here is how common cavity insulation R-values convert. These are center-of-cavity numbers; the whole-assembly U-factor is higher because of framing.

• Counting glazing in both the opaque wall row and the window row. Subtract windows and doors from gross wall area first.
• Entering insulation R-values straight from the label. Use whole-assembly U-factors, since framing and other paths carry heat around insulation.
• Adding two estimates of the same outdoor air stream, such as infiltration plus a ventilation rate that already includes it.
• Using a padded winter design temperature. Use the published design value for your location, then size the system for the load at that condition.
• Reading a heating result as a cooling size. This worksheet has no solar, internal-gain or latent terms, so it cannot give a tonnage.
• Treating this surface-based worksheet as a Manual J. Permits, rebates, and zoned or ductless designs generally require a room-by-room calculation.
• Forgetting what is excluded. Floors over unconditioned space, duct losses, adjacent-space losses and warm-up loads are not in the subtotal.
• Adding a blanket safety factor on top of conservative inputs. It compounds into an oversized system that short-cycles.

A load worksheet is the paper trail behind a heating or cooling number. The structure mirrors the worksheets bundled with ACCA Manual J, the residential load-calculation standard published by the Air Conditioning Contractors of America and referenced by the International Energy Conservation Code (IECC) and many local building codes. The first block of any worksheet captures the design conditions: the outdoor winter (and summer) design temperatures for your location and the indoor setpoints you are designing to. ASHRAE publishes the design temperatures in the Handbook of Fundamentals, often quoted as the 99% heating and 1% cooling values, and Manual J tabulates them by city. These temperatures fix the ΔT that every conduction line depends on. See the post on HVAC design temperature for how they are chosen.

The next block describes the envelope. Each field, such as wall area and U-factor, roof or ceiling area and R-value, window and door area and U-factor, and the infiltration rate in air changes per hour, feeds a separate heat-flow line. U is the reciprocal of R (U = 1 ÷ R), so an R-13 cavity corresponds to about 0.077 before framing effects; lower U means less heat crosses the surface. A full Manual J worksheet repeats this block for every room and then totals the rooms. The worksheet on this page condenses the block into three surface rows and one air row so you can see the heating budget in minutes, then move up to the Manual J calculator when a room-by-room version is required.

The final block reports the result. A full residential report splits cooling into sensible load (the dry-bulb heat the coil must remove) and latent load (the moisture it must condense), because an air conditioner that is correct on total BTU/h can still leave a home clammy if the latent share is high. Heating is a single sensible number driven by the winter ΔT, the envelope and the air leakage. This worksheet reports the heating part only, broken out by row so each term can be challenged.

The point of filling in a worksheet before you call for quotes is leverage. A printed sheet that states your design temperatures, areas, assembly U-factors and resulting BTU/h lets you ask a contractor a direct question: does the Manual J agree with this, and if not, which input differs? Equipment is then selected with ACCA Manual S, which matches the calculated loads to the manufacturer's performance data at the design conditions rather than to the nameplate. Manual S sets limits on how far equipment may exceed the calculated load, and those limits differ by equipment type, so check the current edition. See the Manual S calculator for the selection step.

• Compare inputs, not tonnage: if a quote is well above your worksheet, ask which envelope input, outdoor-air value or safety factor created the gap.
• Bring the design conditions: insist the contractor uses published design temperatures for your location, not a padded outdoor value.
• Check capacity at design temperature: for a heat pump, ask for the capacity at your winter design outdoor temperature, not only the 47°F rating.
• Compare efficiency on the same basis: AFUE for furnaces, HSPF2 and SEER2 for heat pumps and air conditioners, so two units of the same capacity can be compared on operating cost.
• Ask what the quote assumes for ducts: heating loss in leaky or uninsulated ducts is not in this worksheet and adds to the delivered-capacity requirement.

Duct design is the step after sizing. Once the load sets the equipment, ACCA Manual D sizes the supply and return runs to deliver the airflow without excessive static pressure; the duct size calculator and static pressure calculator help with that. Whole-house ventilation is governed separately by ASHRAE 62.2, which sets the minimum fresh-air rate, and you can estimate it with the ventilation calculator. Manual N covers load calculation for small commercial buildings. Keeping these steps separate prevents a single oversized purchase from cascading into noisy, short-cycling ducts.

A completed worksheet is also a document, and others may ask to see it. Some building departments require a load calculation with a mechanical permit for equipment replacement, and some utility or state rebate programs ask for proof that the installed capacity was sized to a real load rather than rule-of-thumb square footage. Requirements vary by jurisdiction and program, and many will specifically ask for a Manual J report, so check what yours accepts before relying on this form. The print-to-PDF button produces a clean single sheet with the on-screen controls hidden so the output reads as a finished record.

For the full method behind these numbers, read how to calculate HVAC load, and see how to measure your home for HVAC for gathering the areas. Keep the PDF with the equipment invoices and the manufacturer's performance data so the whole sizing decision can be reconstructed years later when the system is serviced or replaced. To check other parts of the design, try the furnace size calculator, the heat pump calculator or the U-value calculator.

ASHRAE Handbook, Fundamentals provides heat-transfer, air-property and load-calculation background. Example inputs are stated scenarios, not prescribed handbook values.

For residential design, ACCA Manual J, S and D address load calculation, equipment selection and duct design. This worksheet does not certify a complete design or code compliance. Have a designer complete the omitted losses and provide a proper Manual J report when required for permits or equipment selection.