How to Save on Your Monthly Electric Bill By Installing a Greywater Heat Recovery System

What is a Greywater Heat Recovery System?

A greywater heat recovery system is a type of technology that recovers heat from greywater (wastewater from sinks, showers, washing machines, etc) to pre-heat cold water before sending it to your hot water heater. This allows your hot water heater to use less energy to heat the pre-warmed water, resulting in energy and cost savings.

The system works by installing a heat exchanger that transfers heat between the greywater flowing out of your home and the cold water flowing into your hot water heater. As the warm greywater passes through one side of the exchanger, it heats up the cold water on the other side.

Some key benefits of installing a greywater heat recovery system include:

Lower energy bills - By pre-heating your cold water supply, your hot water heater doesn't have to work as hard which reduces your energy usage. This can save you 10-25% on your monthly hot water heating costs.
Reduced carbon footprint - Since less energy is needed to heat your water, installing a system can lower your environmental impact.
Quick payback period - The costs of installing a system can be recouped in energy savings within 2-5 years in most cases.

How Much Could I Save on My Electric Bill?

The amount you can save on your monthly electric bill depends on several factors:

Climate - Homes in colder climates with a greater difference between cold water inlet and hot water tank temperatures will save more than warmer climates. Savings range from 10-30% typically.
Household size - Larger households with more showers, dishwasher/washing machine loads, etc will recover more heat and energy.
System efficiency - More efficient heat exchangers will capture more heat from greywater and provide greater savings.
Water usage - Households that use more hot water will save more from pre-heating cold water supplies.

As an example, for a family of 4 in a cold climate using 100 gallons of hot water per day, a 50-60% efficient system could save around 15-25% on water heating costs, or $15-35 per month. Actual savings can be determined by an energy audit.

What Are the Costs for Installation?

Installation costs for a greywater heat recovery system range from $800 to $2500 on average depending on the type of system and complexity of installation.

Key factors affecting overall costs include:

Drainwater vs shower drain systems - Shower drain systems are more expensive as they require in-line plumbing under the shower floor. Drainwater systems are simpler.
Copper vs plastic heat exchangers - Copper heat exchangers are more efficient but also more expensive. Plastic models cost less but don't recover heat as well.
Plumbing modifications - Complex drain and venting layouts or lack of space may increase labor time and materials for installation.
Electric vs thermosiphon - Electric pumped systems cost more due to the recirculation pump but offer better efficiency.

Other costs may include permits and professional installation, which can add $200-$500 or more depending on your location. Overall, expect total costs between $1000 - $3000.

How Long Does It Take to Recover the Installation Costs?

Most greywater heat recovery systems have a payback period of 2-5 years. This means the energy savings accumulated over 2-5 years will recoup the upfront costs of purchasing and installing the system.

Factors impacting the payback period:

Installation cost - More expensive systems have longer paybacks. DIY installs can greatly reduce upfront costs.
Energy savings - The greater your monthly savings, the faster you'll reach payback. House size, usage, climate impact savings amount.
Electricity rates - Payback will be quicker in regions with high electricity prices per kWh.
System lifespan - Heat exchangers can last 10-20 years. The longer it lasts, the greater your return on investment.

As an example, for a $1500 system in a 4-person household saving $25/month on electric bills, the payback period would be 1500 / 25 per month = 60 months or 5 years. After payback is reached, the system would continue providing savings for many more years.

What Are the Steps for Installing a Greywater Heat Recovery System?

Installing a greywater heat recovery system typically involves the following key steps:

Choose a location - Identify the best location for the system, which is typically in a basement or utility room near the water heater and drain lines.
Select a system - Choose an appropriate greywater heat recovery system for your home based on number of bathrooms/occupants, efficiency needed, and budget.
Install plumbing - A professional will need to install drainage and cold water supply plumbing modified to integrate with the heat exchanger.
Mount heat exchanger - Securely mount the heat exchanger in place once plumbing is ready. Clamps, wall-mounts, or stands are used.
Connect piping - Connect the greywater outflow and cold water inflow pipes to the proper ports on the exchanger.
Insulate piping - Insulate any exposed drainage or cold water pipes to maximize heat recovery potential.
Start system - When ready, start flowing greywater through the system. Flush pipes first to clear any debris.
Test and adjust - Monitor temperatures and water flows for the first weeks and make any needed adjustments.

Are There Any Maintenance Requirements?

Greywater heat recovery systems are relatively low maintenance, but a few minor maintenance tasks are recommended:

Inspect for leaks - Periodically inspect the system for any leaking connections or corroded parts. Fix any leaks immediately.
Flush annually - Flush the system with water each year to clear out any built-up sediment or debris.
Check vents - Ensure vent lines are clear of obstructions to avoid pressure build-ups.
Clean filters - Drainwater systems have a filter that needs cleaning every 6-12 months.
Check pipe insulation - Replace any damaged or worn pipe insulation to maintain heat recovery performance.
Verify temperatures - Check the temperature rise across the system yearly to ensure proper operation.
Replace if needed - Eventually, the heat exchanger or pump may need replacement after 10+ years.

Proper maintenance will extend the operating life and effectiveness of a greywater heat recovery system.

Are There Any Concerns or Considerations With These Systems?

Some important considerations before installing a greywater heat recovery system:

Drain capacity - Your drains must be able to handle the additional greywater flows from the heat exchanger system.
Venting - Proper venting is crucial to allow air flows and prevent trap gurgling or vacuum lock.
Freezing climate - Outdoor drainage pipes could freeze in cold climates, interrupting operation. Insulation helps prevent this.
Condensation - These systems produce condensation that needs to drain properly without damage. Insulation helps reduce this.
Backflow prevention - A backflow preventer on the cold water line is required to ensure greywater never backs up into clean water pipes.
Local codes - Your municipality may have specific regulations, permits or codes for greywater systems. Check first before installing.

With proper system selection, installation and maintenance, greywater heat recovery systems provide an effective means to lower monthly hot water costs and environmental impact.

In Summary:

Greywater heat recovery systems can save 10-25% on monthly water heating bills by pre-heating cold water entering the hot water heater.
Installation costs range from $800-$2500 depending on type and complexity. Energy savings accumulated over 2-5 years typically pay back installation costs.
Choosing the right system and properly installing drainage, plumbing, heat exchanger, and vents are key steps for installation success.
Minimal maintenance like flushing, insulation, and leak checks helps ensure systems continue working effectively for many years.
Paybacks of 2-5 years from energy savings make these systems a smart investment to lower electric bills and your carbon footprint.