TOWNSEND -- "It was definitely a project house," Zachary King said looking around his family's home on Turner Road.

King and his wife, Marisa, moved into the home in 2003. They have renovated and painted over the years.

The biggest and latest project is almost done -- an addition that adds living space, more basement room and a large, two-car garage.

How to heat the new space was a big decision. The existing oil burner was just not big enough for the addition and the house.

The couple considered oil, wood, natural gas, propane and geothermal.

Meetings with contractors and creating 18 spreadsheets helped them make their unusual decision -- geothermal.

Zachary made all the spreadsheets; he is an engineer, Marisa said. Cost and ease-of-use were important factors in deciding on the heating system.

"We looked to bring in natural gas. It's a lot cheaper than propane," Zachary said.

There was just one problem with that plan. The fuel is cheaper but the cost to bring a gas line in from Warren Road would have been about $100,000. There was no negotiating with Unitil.

"They'd need on the order of 40 houses" to put in a line, he said.

Like propane, oil heat is more expensive than gas, and all have the same problem. The prices are volatile. There is no telling what the cost might be a few years from now.

That left wood and geothermal heat on the couple's list.

No strangers to wood, the couple has used it as supplemental heat for years.

But wood heat takes a lot of attention. Between raising two young daughters and her work as an occupational therapist, Marisa did not think she could be home consistently enough to keep the home fires burning.

That left geothermal.

Installers came in to discuss the options. Tax credits and a zero percent loan would make such a system only a few thousand dollars more than an oil system.

It was looking better and better.

Geothermal heat is a rare thing in Townsend. The Workers Credit Union branch in the center installed a system a few years ago. Carter Scott, the developer of an ultra energy efficient subdivision on Coppersmith Way, installed a system in his own home.

Zachary began the municipal permitting process. It took some time and lots of meetings before the system finally got the go-ahead.

The 300-foot well was dug to 600 feet to accommodate the coils. Water pumped into the house is used to run the climate-control system and for domestic use.

Once water has been used to create the heated or cooled air needed, depending on the season, it is returned to the well at almost the same temperature it had when it was pumped out, Zachary said.

"The earth is so big, the little bit of energy we take is negligible," he said.

The system will run more often than the oil-burner did because the temperature emitted from the furnace is not as hot. This means using more electricity.

The Kings have that covered too. Some of that demand will be taken up by the solar system at the house.

They expect to see an increase of $100 per month for electricity. Oil would have cost about $800 per month for a larger system, they said.

As an added bonus, the geothermal system will pay for itself, they say, in seven years.