If you need more proof that big-box home-improvement retailers are sold on the home-energy retrofit business, here it is.

Home-energy remodeler/software developer Recurve said Wednesday that it had raised another $8 million. High on the list of investors is Lowe's Companies, the North Carolina-based home products chain with 1,700 stores in the United States and 14 million customers.

The retailer, which has been courting renewable energy companies in recent months, made a $4 million equity investment in the San Francisco startup, joining existing investors RockPort Capital Partners and Shasta Ventures. The investment doubles to $16 million the money Recurve has raised since its founding six years ago.

CEO Pratap Mukherjee says the unusual investment is evidence of Lowe's continued interest in its year-long partnership with Recurve. The two companies market a co-branded energy-audit and retrofit service in a handful of Lowe's stores in the San Francisco Bay area. Lowe's also sellssolarpanels from Akeena Solar.

The arrangement has been successful, says Mukherjee, who declined to offer sales figures or deal volume. It also isn't likely to be the last among energy contractors and home-products companies.

Apparently just about every big retailer and home products company is eyeing the retrofit business with increasing interest, including big names such as Home Depot, Masco and Johns Manville.

Several have already made stabs at the market. In March, Masco launched its WellHome energy audit and retrofit service in seven cities with plans to expand by the end of the year.

Home Depot has a consumer website where homeowners can self-diagnose home energy efficiency. The company also struck a deal this year to have SolarCity install solar panels for its customers.

With 70 million homes in the U.S. in need of $10,000 energy retrofits, "I think everybody sees the tremendous potential," says Mukherjee.

Recurve, formerly Sustainable Spaces, says it will use the new money to expand its suite of energy-retrofit software and to add to its sales and service staffs.  

The company formally unveiled the first module of the software in April, showcasing a program designed to automate home energy audits, although it has been discussing its software for months. (Greentech Media picked it as a top-ten green software company last August.) Recurve has 10 contractors using the beta product and plans a commercial release in the third quarter. If the software can be shown to accurately predict energy savings, it could be used as a way for utilities to reduce power consumption across a region.

The software should be a boon for business. Two hundred companies across the U.S. have expressed interest in using it, says Mukherjee.