Size recovery for garden wash stations and heaters. Switch units, add costs, and save results. Know refill timing before chores start, every busy morning.
Energy (BTU) = Volume(gal) × 8.34 × ΔT(°F). Effective Output (BTU/hr) = Input(BTU/hr) × Efficiency. Recovery Time (hr) = Energy ÷ Effective Output.
Recovery Rate (gph) = Effective Output ÷ (8.34 × (Target − Incoming)).
| Use case | Tank | Input | Temps (inlet→target) | Typical goal |
|---|---|---|---|---|
| Greenhouse hand-wash sink | 20 gal | 3.0 kW | 55°F → 110°F | Quick reheat between shifts |
| Tool rinse station | 40 gal | 4.5 kW | 60°F → 120°F | Steady hot water for cleaning |
| Mixing nutrient solution | 80 gal | 18,000 BTU/hr | 50°F → 100°F | Reduce shock in cold months |
| Outdoor hose bib (seasonal) | 30 gal | 12,000 BTU/hr | 45°F → 105°F | Warm water for delicate plants |
| Small greenhouse shower | 50 gal | 6.0 kW | 60°F → 125°F | Fast recovery after short bursts |
Tip: Colder inlet water increases ΔT and reduces recovery rate.
Warm water supports hand washing, tool sanitation, and gentle irrigation cleanup. This calculator estimates how long a tank needs to climb from its current temperature to your working setpoint. Many growers aim for 105–125°F for cleaning, while avoiding scald risks at sinks.
Heating demand is driven by gallons stored and degrees of rise. A 40‑gallon tank with a 60°F rise needs about 40 × 8.34 × 60 ≈ 20,016 BTU. If you store 80 gallons, energy roughly doubles. In winter, inlet water can drop from 60°F to 45°F, increasing rise and reducing usable hot water.
Electric elements are commonly listed in kW, while gas units use BTU/hr. The calculator converts units and multiplies by an efficiency factor to reflect heat delivered to water. Typical electric efficiencies are 0.90–0.98, while older atmospheric gas heaters may be 0.70–0.85. A 4.5 kW element equals about 15,354 BTU/hr; at 0.95 efficiency, effective output is about 14,586 BTU/hr.
Full‑tank recovery time helps schedule chores after heavy draw, such as washing harvest bins or refilling a mop sink. For the example above, 20,016 BTU divided by 14,586 BTU/hr is about 1.37 hours, or 82 minutes. Recovery rate in gallons per hour is more useful during steady use, because it estimates how fast cold supply can be reheated from inlet to target.
For sizing, compare recovery gph to expected draw. Two low-flow taps at 1.0 gpm each require 120 gph. If recovery is lower, plan pauses or a larger heater during peak.
Energy use tracks the temperature rise, so reducing the target by 5°F typically cuts heating energy by about 5/60 ≈ 8% in a 60°F rise scenario. Insulating the first 6–10 feet of hot piping, fixing leaking mixing valves, and lowering standby hours also improve results. Save the CSV or PDF report for maintenance logs and seasonal comparisons.
Use incoming as your cold supply, initial as the current tank temperature, and target as the setpoint you need for work. If you are unsure, measure with a probe thermometer at the tank drain or a nearby tap.
Water heating math is commonly expressed in BTU using 8.34 BTU per gallon per °F. The calculator converts liters and kW automatically, then reports results in practical minutes and gallons per hour.
For electric storage heaters, 0.90–0.98 is typical. For older non‑condensing gas units, 0.70–0.85 is common. Use a lower value if the heater is outdoors, poorly insulated, or frequently short-cycles.
It estimates how many gallons per hour can be reheated from inlet temperature up to the target. Compare it with your expected draw; if you draw faster than recovery, outlet temperature will fall during continuous use.
Cost uses the kWh-equivalent of the heat added to the water. Actual bills can differ due to standby losses, piping losses, and demand charges. Use it for comparing scenarios and spotting large efficiency opportunities.
Yes. Enter the tank volume you heat and the temperatures you operate at. For open mixing tanks, expect extra losses to air; using a slightly lower efficiency factor helps keep schedules realistic.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.