# Home Energy & Electrical calculators

> HVAC BTU sizing, heat loss through walls, room lighting, circuit load and breaker sizing, EV charging time and running cost, fuel versus electric cost, solar payback, rainwater harvesting, water heating energy, generator sizing, ventilation.

12 calculators. HTML index: https://tttkmbb.com/energy · JSON: https://tttkmbb.com/api/v1/calculators?category=energy

- [HVAC BTU Sizing Calculator](https://tttkmbb.com/energy/hvac-btu-sizing.md): Estimates the cooling capacity (BTU/h, tons, kW) and heating output a room needs from floor area, ceiling height, climate, sun exposure, insulation, occupants and kitchen heat, using the 20 BTU/h per ft² rule of thumb with the ENERGY STAR room air conditioner adjustments. Tool: `estimate_hvac_btu_sizing`.
- [Heat Loss Calculator](https://tttkmbb.com/energy/heat-loss.md): Computes the steady-state conductive heat loss through a building element from its area, its thermal transmittance (U-value, or an SI or imperial R-value) and the inside–outside temperature difference, with the daily and monthly energy and the cost at an electricity price. Tool: `calculate_heat_loss`.
- [Room Lighting Calculator](https://tttkmbb.com/energy/room-lighting.md): Computes the lumens a room needs from its floor area and a target illuminance (by room type or a custom lux value) divided by a light-loss factor, then the number of bulbs and the wattage at a given luminous efficacy. Tool: `calculate_room_lighting`.
- [Circuit Load Calculator](https://tttkmbb.com/energy/circuit-load.md): Adds up the appliance wattages on one branch circuit, converts them to amperes at the given voltage and power factor, compares the load with the breaker rating (applying the NEC 80 % continuous-load limit when requested) and recommends the smallest standard breaker size that fits. Tool: `calculate_circuit_load`.
- [EV Charging Time Calculator](https://tttkmbb.com/energy/ev-charging-time.md): Estimates how long an electric vehicle takes to charge between two states of charge from its battery capacity, the charger power (capped by the onboard charger for AC charging) and the charging efficiency, plus the energy drawn from the grid and its cost. Tool: `estimate_ev_charging_time`.
- [EV Range and Efficiency Calculator](https://tttkmbb.com/energy/ev-range-efficiency.md): Converts an electric vehicle's energy consumption between Wh/km, kWh/100 km, Wh/mile, mi/kWh and km/kWh, computes the driving range from the battery capacity and usable share, and reports the EPA MPGe equivalent (33.7 kWh per US gallon of gasoline). Tool: `calculate_ev_range_and_efficiency`.
- [Fuel vs EV Cost Calculator](https://tttkmbb.com/energy/fuel-vs-ev-cost.md): Compares the annual energy cost of a combustion car (L/100 km × fuel price) with an electric car (kWh/100 km × electricity price) over the same distance, and reports the savings, cost per km and the years needed to recover an EV price premium. Tool: `compare_fuel_vs_ev_cost`.
- [Solar Payback Calculator](https://tttkmbb.com/energy/solar-payback.md): Estimates the annual generation of a photovoltaic system from its size and specific yield, the first-year savings from self-consumed electricity and exported energy, the simple payback period, and a year-by-year table with panel degradation and electricity price escalation over the analysis period, including the levelised cost of the solar electricity. Tool: `estimate_solar_payback`.
- [Rainwater Harvesting Calculator](https://tttkmbb.com/energy/rainwater-harvesting.md): Computes the rainwater a roof can collect per year from its horizontal area, the annual rainfall and a runoff coefficient, the litres captured per millimetre of rain, and, given a daily demand and tank size, the days of supply a full tank covers and the share of demand the yield meets. Tool: `calculate_rainwater_harvesting`.
- [Water Heating Energy Calculator](https://tttkmbb.com/energy/water-heater-energy.md): Computes the energy needed to heat a volume of water by a given temperature rise (specific heat of water 4.186 kJ/(kg·K)) at a heater efficiency, the daily and annual energy and cost for repeated heating, and the heating time for a given heater power. Tool: `calculate_water_heating_energy`.
- [Generator Sizing Calculator](https://tttkmbb.com/energy/generator-sizing.md): Estimates the generator size needed for a set of loads from the total running watts, the starting surge of the largest motor (peak = running total + starting − running of that motor), a safety margin and the power factor, giving the required kW (rounded up to 0.5 kW) and kVA plus the running current at 120 V and 230 V. Tool: `estimate_generator_size`.
- [Air Changes per Hour Calculator](https://tttkmbb.com/energy/air-changes-per-hour.md): Computes the air changes per hour of a room from its volume (or dimensions) and the ventilation airflow in m³/h, L/s or CFM, converts the airflow between units, and gives the airflow needed to reach a target ACH, with typical design values from ASHRAE standards. Tool: `calculate_air_changes_per_hour`.