🛁 Indirect Water Heater Sizing Calculator
Find the right indirect water heater tank size for your household—enter your details below for an accurate recommendation.
1–2 BR
2–3 BR
3–4 BR
4–5 BR
5+ BR
High Demand
(gallons)
(gallons)
| Fixture / Appliance | Gallons (gal) | Liters (L) | Notes |
|---|---|---|---|
| Standard Shower (8 min) | 17–20 gal | 64–76 L | At 2.0–2.5 gpm |
| Low-Flow Shower (8 min) | 12–14 gal | 45–53 L | At 1.5 gpm |
| Standard Bathtub | 30–40 gal | 114–151 L | Half fill hot |
| Jetted / Soaking Tub | 60–120 gal | 227–454 L | Full fill hot |
| Dishwasher (cycle) | 6 gal | 23 L | Per wash cycle |
| Clothes Washer (hot load) | 7 gal | 26 L | Per load |
| Kitchen Sink (per use) | 2–4 gal | 8–15 L | Washing dishes by hand |
| Bathroom Sink (per use) | 0.5–1 gal | 2–4 L | Hand washing / grooming |
| Boiler Type | Typical BTU/hr | Recovery Rate | Recommended Tank |
|---|---|---|---|
| Oil Boiler | 80,000–120,000 | 1.5–2.5 gpm | 30–50 gal |
| Gas Boiler | 60,000–100,000 | 1.0–2.0 gpm | 40–65 gal |
| Propane Boiler | 60,000–100,000 | 1.0–2.0 gpm | 40–65 gal |
| Electric Boiler | 10,000–24,000 | 0.3–0.8 gpm | 50–80 gal |
| Geothermal | 24,000–48,000 | 0.6–1.2 gpm | 50–65 gal |
| Heat Pump | 10,000–20,000 | 0.3–0.6 gpm | 65–80 gal |
| Tank Size | Typical FHR (gal/hr) | FHR Metric (L/hr) | Best For |
|---|---|---|---|
| 30 gal / 114 L | 40–50 gph | 151–189 L/hr | 1–2 people |
| 40 gal / 151 L | 50–65 gph | 189–246 L/hr | 2–3 people |
| 50 gal / 189 L | 65–80 gph | 246–303 L/hr | 3–4 people |
| 65 gal / 246 L | 80–100 gph | 303–378 L/hr | 4–6 people |
| 80 gal / 303 L | 100–130 gph | 378–492 L/hr | 5–8 people |
| 115 gal / 435 L | 140–180 gph | 530–681 L/hr | Commercial / 8+ people |
Indirect water heater is kind of system that is useful the domestic heating system for warm water. You know them also as sidearm tank. Rather than independent device with its burner, it takes heat from already available boilers or furnace.
The boilers accomplish everything, and the indirect heater only help to hand over the heat. That solution well answers for boiler heating.
How Indirect Water Heaters Work
The way of this system base on heat change. Boilers or furnace heats liquid, usually water or antifreeze mixture. The liquid circulates through spiral tube in insulated water tank.
Like this it heats the water in the tank for later use. It is important, that the heated liquid never mingles with domestic water in the tank. Basically it is exchange tank: the heated liquor passes through it to heat water for hot water.
Using indirect water heater are very efficient. The water tank can preserve energy, allowing the boilers turn off less often. For families with high need of warm water, many models deliver quick hot water recovery.
For instance, the PowerStor-series of single wall models use unique wall exchanger. That construction gives faster water delivery and better heat transfer. Most of indirect tanks do from quality stainless steel for optimal warming and long service.
Well installed, it can serve 20 until 30 years, during electric heater commonly only ten.
When you plans to buy such, the size is inherent. If you do not have problems with warm water now, a properly sized and installed indirect heater will give more water, no less. Because it feeds of boilers with commonly more than 40 000 BTU, a lot surpassing standard 40 000 BTU direct heater.
Generally they coincide with any fuel source. Some uses them as buffer tank to stabilise water temperature. Without combustion chamber are also less risks of failure.
