面積、天井高、断熱性、気候帯、日当たり、居住人数を使った簡易Manual-J方式で、エアコン・ヒートポンプ・ヒーターの最適サイズを算出。
| 内訳 | BTU/hr |
|---|
簡易版Manual-J方式: 基準値20 BTU/sqft × 面積 × 断熱性能 × 気候 × 日射で算出し、天井高(基準8ft/2.4m)に応じて調整します。
さらに使用人数1人あたり600 BTUを加算し、キッチンの場合は家電の発熱分として+4000 BTUを加算します。
トン数: 冷房能力1トン = 12,000 BTU/hr。 kW(ヒートポンプ出力): BTU/hr ÷ 3412。
最終的な機種選定は、必ず有資格のHVAC業者によるManual-J負荷計算で確認してください。このツールはあくまで初期見積もり用です。
This is a Manual-J-lite heuristic, and the breakdown table shows each step. It starts at 20 BTU/hr per square foot of floor area, multiplies by three modifiers for insulation, climate zone and sun exposure, then scales by ceiling height divided by 8 feet, so a 10 foot ceiling adds 25 percent. Occupants add 600 BTU each and ticking Kitchen adds a flat 4,000 BTU. Heating mode multiplies the total by 1.10. Tonnage is BTU ÷ 12,000 and kW is BTU ÷ 3,412.
The three multipliers are where your judgement matters. Insulation runs Good 0.85, Average 1.0, Poor 1.15. Climate zone runs Hot (zone 1-2) 1.20, Warm (zone 3) 1.10, Moderate (zone 4) 1.0, Cool (zone 5-6) 0.95, Cold (zone 7-8) 0.90. Sun exposure runs Heavily shaded 0.9, Normal 1.0, Sunny (south/west facing) 1.1. The four presets simply set the area: Bedroom 150, Living room 300, Open plan 500, Whole floor 800 square feet.
The climate multipliers are written for cooling, where a hotter zone means a bigger load, and they are applied unchanged when you switch to Heating — so a cold zone still reduces the number even though heating demand rises with cold. In heating mode the only adjustment is the flat 1.10. Nothing models window area, orientation, air changes, duct losses or floor position. Use this to narrow the shortlist, then get a real Manual J from an HVAC contractor before buying.
On the defaults — average insulation, moderate climate, normal sun, 8 foot ceiling — 500 sqft gives 10,000 BTU/hr, plus 600 per occupant. Two occupants brings it to 11,200 BTU/hr, or 0.93 tons, so you would shop for a 12,000 BTU unit.
Because the load scales with volume, not floor area. The tool divides your ceiling height by the 8 foot baseline and multiplies the adjusted base by that ratio, so a 12 foot vaulted ceiling raises the requirement by 50 percent over the same footprint.
Set Kitchen to Yes and the tool adds a flat 4,000 BTU on top of the area-driven figure, covering oven, cooktop and refrigerator heat. It is a fixed amount, not a percentage, so it matters much more in a small galley than in an open-plan space.
Both appear under the main result. One ton of cooling is 12,000 BTU/hr, so the tool divides by 12,000, and kilowatts come from dividing BTU/hr by 3,412. Tons is how North American AC and heat pump capacity is usually labelled.
Only as a very rough first pass. Switching Mode to Heating adds a flat 10 percent, but the climate multipliers were built for cooling loads and still reduce the figure in cold zones. For heating in a cold climate, treat the result as a floor and get a proper load calculation.
Concrete Volume & Bags Calculator
Cubic yards / metres of concrete needed for slabs, footings, columns and posts, plus bags-of-mix conversion.
Paint Coverage Calculator (Litres / Gallons)
Litres or gallons of paint needed by wall area, coats, primer and surface texture coverage.
Lumber Board Feet & Cost Calculator
Calculate board feet, linear feet and total cost for hardwood and softwood lumber.
Tile & Flooring Coverage Calculator
Tiles or boxes needed for any floor or wall area, with pattern waste and grout lines.
MIG Welding Settings Calculator (Amps, Volts, Wire Speed)
Recommended MIG welding voltage, amperage and wire feed speed by metal thickness, wire diameter and material.
Landscaping Material Calculator (Gravel, Mulch, Soil, Sand)
Cubic yards, weight, bags and cost of gravel, mulch, topsoil or sand needed for any area and depth.
