Bringing it Home: My Heat Pump

I live in an old house that used to be heated by an oil-fired steam boiler in the basement. It was a single pipe steam system, which meant that the steam ran out to all the radiators, condensed, and then the condensate ran back to the boiler via the same pipe. And it worked great. It didn’t bang the way many of those systems do, and the whole house held comfortably at 68°.

But when oil hit $6 per gallon where I live in Falmouth, Massachusetts, I got to thinking. There are about 5840 heating degrees days in this part of the world, and we are getting about 5.5-degree days per gallon, which means we use about 1100 gallons per heating season. That means it would cost us about $6,600 during the winter to heat the house. There are a lot of other things I could do with that money! And—to top it off—we lug air conditioners in and out of windows seasonally.

I am not fond of the idea of ripping out walls and ceilings to install the big metal ducts that conventional conditioned air systems require. Small diameter, high velocity systems like the SpacePak or Unico deliver the air through 2-inch diameter ducting, which can be snaked through 2 x 4 wall cavities. Plus, MassSave—our local collaborative of Massachusetts’ electric and natural gas utilities and energy efficiency service providers—had a $10,000 incentive to replace fossil fuel systems with heat pumps and that helped us take out a major piece of the cost.

SpacePak has an air to water heat pump that takes advantage of the fact that water can efficiently carry much more heat that air can. They offer their system in a “monobloc” configuration. That means that the system is delivered to the job fully charged and ready to be plugged in. If there are future advance in refrigerant technology, the old system can be easily replaced by a new, charged system.

We heat our hot water with a side-arm tank on the oil boiler. With the SpacePak system, we can heat the domestic hot water with the heat pump.

The heat pump system in this old house of mine was completed in April of 2023, and I switched the thermostat on the steam heating system to off for the first time.

The improvement in efficiency is spectacular. This old house has had just about every heating system. It had wood stoves in individual rooms. It had a gravity driven coal fired hot air system. I built a fan driven solar room on the south wall. And for back-up, we have a Jotul Combi-4 wood stove. Adding a state-of-the-art air to water heat pump just seems like logical next step.

This is a whole-house system. The air handler for the second floor is in the attic with ducts running to all the upstairs rooms and the thermostat is in the master bedroom. On the first floor there are four individual “heads.” All five of these systems are connected to one outdoor unit. The house is in a historic district so there are only two refrigerant lines on exterior walls. All the other lines are internal running down interior walls and through very old chases.

A cubic foot of air can only hold 0.018 BTU/ ft3 /°F. A cubic foot of water, on the other hand, can hold 62.4 BTU/ft3/°F. So, you have to move a lot more air to heat up a room. A hydronic (water) or steam system can be set back at night, and then pour the heat into the building in the morning to warm it back up. When switching to a heat pump system, it is most energy efficient to keep the temperature in the house stable.

This system is so quiet that I have put streamers on the grilles to make sure that it’s working. I have thermometers everywhere, and I am amazed at how stable the temperatures are throughout the house. But it is a different way of thinking. We’re going to have to learn to get along. Especially now that we have AC throughout the house. No more bulky window air conditioners. Yay!