Cutting the Heating Bill by Closing off Unused Rooms

Our 1924 home has a hot water boiler system. We replaced the old boiler with a natural gas, 95% efficient boiler when we purchased the house. Our home has three floors with a full attic. On the third floor, there are six rooms, bedrooms and bathrooms, that we use only when we have overnight guests. My question is: What is the best way to reduce our heating costs when these rooms are not being use? Should we close the doors and turn off the hot water to the radiators?

Closing off unused spaces and turning down the heat is certainly going to help. But by how much depends on whether your house has been insulated and air-sealed. Those weren't top priorities in 1924, so unless your house has had some remedial work in the meantime, you may not save as much energy as you'd like.

What you're fighting is called the stack effect, the upward movement of warm air. As heated air leaves the top of the house through leaks around windows or tiny gaps in walls, cold air is drawn in from the outside on the first floor.

This is what building scientists tell us is going on, but seeing it first-hand can make you a believer.

My daughter and her husband once lived in a fourth-floor apartment in New York City. It was old housing stock, and it wasn't especially well sealed or insulated. During the winter, it was suffocatingly hot in their apartment even though the radiators were completely turned off. I bet tenants on the first floor were pretty chilly.

That's the stack effect.

In your case, any air leaks between the second and third floor allow a surprising amount of heat to migrate upward through the second-floor ceiling. Gaps around pipes and wires, ceiling light fixtures, and chimney chases provide great avenues for escaping warm air. The stairway to the third floor is a veritable Holland Tunnel of heat loss.

Further, it is unlikely there's much if any insulation between the two floors. After all, builders don't usually insulate these spaces unless they know in advance an upper floor will occasionally be an "unconditioned" space.

A house with six rooms on the third floor has got to be a big one. If you're serious about cutting your fuel bill, consider an energy audit. Get some specially trained technicians who crawl all over your house and figure out where you're losing energy. They might suggest a general tightening up, replacing old windows, or adding insulation.

It's up to you to decide how many of their recommendations are worth pursuing.

You might also contact a heating contractor to find out whether you have any options for zoning the hot water heating system that are more effective than simply shutting off the radiators in rooms you're not using.

You've already made an important investment. Dumping the old boiler and replacing it with a high-efficiency model saves a fair amount of energy over the course of a heating season. Following that up with an energy audit is a logical next step. Either that or consider renting out the third floor and using the proceeds to offset your gas bill.