Small space, high efficiency

Squeezing a new combi boiler into a basement remodel

combi water boiler
A combi water boiler works as a water heater and also distributes that hot water to the pipes to heat up the home (r). Photo courtesy of Applied Energy

When Zach Zins and Tricia Brown decided to do a full-scale remodel of the basement in their Seward home, they realized they were going to need a new heating source.

Their modest-sized three-bedroom home, built in 1912, includes a roughly 600-square-foot partially finished basement that Zins described as “a little ratty.” It was last remodeled three decades ago.

Zins and Brown are planning to turn the basement into a master bedroom, one that guests, their daughter or even Airbnb users could stay in. To make that plan a reality, the basement will need to be warm during the winter.

Because the floor is made of cement, which gets cold during the winter, Zins and Brown decided to go with in-floor heating for their remodel. Their full-scale remodel, which began last year, consists of tearing out the basement’s existing slab and replacing it with a new one that will be heated with water tubes.


Zins and Brown contracted with Uptown-based OA Design+Build+Architecture to install a new boiler that will heat the new basement floor.

To save money and energy in the long haul, they opted for a high-efficiency boiler, with the hope that it may one day serve as the primary source of heating for their house. Currently, they rely on forced air heating from a furnace, which Zins said is costly and makes the air in his home dry during the winter.

“Even if we break even, I think we will be happy,” Zins said, weighing hoped-for long-term savings against the cost of the overhaul.

The boiler that ended up in his basement is compact, installed in a tight location behind the stairs. It’s a stark contrast to older, conventional boilers, which are often large enough take up the bulk of a room.

Zins and Brown’s new boiler is roughly 2 feet long and a foot-and-a-half wide and deep.

“I could pick it up and carry it under my arm,” Zins said.

It’s called a combi boiler because it works as a water heater and also distributes that hot water to the pipes to heat up the home. They typically cost $2,000–$5,000 to install.

standard water boiler
A standard water boiler. Submitted photo

Improved efficiency

Part of what makes Zins and Brown’s boiler efficient is its sealed combustion.

Standard boilers use an open flame and share air with the home to keep the flame going. In the case of a high efficiency boiler, that flame is sealed off and uses only air from the outside through an insulated pipe. It doesn’t share air with the house, which Michael Anschel, principal of OA, said is unsafe.

Standard boilers use a metal pipe attached to the top to exhaust gas from the flame through a chimney. As the boiler heats the house, the metal pipe gets hot, which wastes a good chunk of the heat that could otherwise be distributed through the house.

“In that process we’d throw away 30 percent of the heat,” Anschel said.

The combi boiler instead uses an exhaust pipe made from polyethylene plastic, which traps much of the heat normally exhausted with the gas. Anschel estimates that this allows the boiler to use 96–98 percent of the heat produced to warm the water pipes.

And even though Zins and Brown are adding an entirely new heating system into their house, the heating bill won’t cost more, Anschel said.

To explain why, he cited the first law of thermodynamics, which basically amounts to energy moving from more to less. In other words, heat from the boiler will move from the floor to the rest of the house.

That means that Zins and Brown should be able to rely less on the forced-air heat from their furnace in the future.

Waiting for savings

Other improvements should help, too. OA put gravel and 3 inches of insulation into the ground before installing the new slab in the basement.

Still, Zins and Brown won’t get to test out their energy savings until next winter. Remodeling on their basement won’t be completed until spring, so they haven’t started using the new boiler yet. But Zins is anxious to compare the heating costs from this winter to next winter when the time comes.

“Believe me, I’m saving the energy bills,” he said.