Drain Water Heat Recovery Calculator
Calculate the energy and cost savings of installing a Drain Water Heat Recovery (DWHR) system to capture heat from your showers.
Table of Contents
Shower Usage
System & Energy
Typical units range from 30% to 50% efficiency.
Savings Analysis
10-Year Outlook
How Drain Water Heat Recovery Works
A Drain Water Heat Recovery (DWHR) system is a copper heat exchanger that replaces a vertical section of your main shower drain line. As warm water flows down the drain, it clings to the inside of the copper pipe.
Cold incoming water flows through a coil wrapped around the outside of the drain pipe. The heat transfers from the drain water to the cold water, preheating it before it reaches your water heater or shower mixing valve.
Key Requirements
- Vertical Drain: Requires a vertical drop (usually 36" to 60") in the drain line below the shower.
- Simultaneous Flow: Only works for activities where water is draining at the same time it is being used (like showers). It does not save energy for baths or washing machines.
- No Moving Parts: DWHR systems have no moving parts, require zero maintenance, and typically last 30-50 years.
Drain Heat Recovery Formula
A copper heat exchanger wraps around your main drain stack, preheating the incoming cold water line using heat from falling shower water before it enters the water heater.
Formula Used
Recovered Energy = GPM * 8.33 * Shower Duration * Temp Rise * Exchanger Efficiency
Reference Quick Chart
| Exchanger Length | Typical Heat Transfer % | Average Annual Energy Saved |
|---|---|---|
| 36 Inches | 35% - 40% | 800 - 1,200 kWh / yr |
| 48 Inches | 45% - 50% | 1,200 - 1,600 kWh / yr |
| 60 Inches | 55% - 60% | 1,600 - 2,000 kWh / yr |
Recommended Water Heater Products
Tankless Water Heaters
Save up to 50% on energy costs with an endless supply of hot water. Best for active, multi-shower households looking to cut utility bills.
Storage Tank Water Heaters
Reliable and affordable upfront solutions. Delivers high peak-hour volume to ensure you never run out of hot water during busy mornings.