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When you add space, you may need to upgrade your heating system.

This time of year, you should be deeply involved in the plans for your spring and summer projects. Our article on “Planning for Spring Projects” covers planning, timing, budgeting, and choosing a contractor, and it points out that now is the time to get on your contractor’s schedule if you want to get any major project completed by a specific deadline.

If your plans include adding more living space to your home, whether it’s finishing the attic or basement, breaking through into an attached shed or garage, or putting on a completely new ell, one of the side effects you can’t afford to overlook is the increased heating load. Will your current heating system be able to handle it?

The Well Designed Heating System

In a well designed home, the heating system is sized to match the living space. It needs to be able to provide enough heat to keep all the rooms comfortable in the dead of winter, while using as little fuel or electricity as possible. If the heating system is too small, it has to work overtime to provide enough heat. This will result in some rooms being too chilly and can shorten the life of the system. Paradoxically, it can also waste energy, because it’s not running at its most efficient rate.

On the other hand, a heating system that’s too large is also less efficient, because it cycles less frequently than it’s designed for. The architect or heating/mechanical engineer probably knew this when he designed the system for your home. Unless they had specific instructions to plan for an addition a few years down the road, the current system is likely to be too small for the addition of your dreams.

Upgrades to Your Heating System

A good heating/mechanical contractor will be able to tell you if your heating system needs an upgrade after he has seen your plans. (And your general contractor should be able to recommend one or two specialists to contact.) If the answer is yes, the next question is, what type of upgrade should I install?

If you have either a radiant-hot-water or a forced-hot-air system, you have the option of replacing the furnace or boiler and then running ducts or pipes into the new living space. However, there are other options to consider that may be cheaper and more energy efficient.

Radiant Floor Heating

Radiant Floor Working

If you are adding on a room or finishing an attached shed, you might want to consider building it on an insulated concrete slab that has pipes or ductwork laid into the slab. The hot water or air running through the floor provides a very efficient and comfortable way to heat a room. (Warm feet in the winter!) The slab can be finished with tile and softened with area rugs.


Hot water works best in this situation, but hot air can be used if done properly. You can also run heating under the wooden floor of a newly finished attic, but the slab installation is more effective, both in terms of comfort and energy efficiency. Overheating a wood floor can cause expansion and warping, too.

Heat Pumps

Rather than upgrading your boiler or furnace, you can heat the new space with a completely independent heating system. This has the advantage that you can shut it way down or completely off if the new space is only used for special occasions. Wood stoves and efficient propane space heaters are both good options in this situation, but you should also consider a modern heat pump.

Heat pumps are somewhat magical. Using the same technology that expells heat from inside your refrigerator, these systems extract heat from the outdoors and pump it into your house. The amazing part is that the new versions can do this even when it’s 18 below zero outside!

Heat pumps are also quite energy efficient, because it takes less energy to move heat than it does to make it. And, in the summer, they can be reversed to move the heat out of the house, so there’s no need for a separate air conditioner.

At the coldest time of the winter, heat pumps sometimes need a little extra help, but a wood stove, a small electric baseboard unit, or a fan to blow air from the rest of the house can fill that need. The blowers and compressors in some heat pumps can also be noisy, so you need to quiz the supplier and installer carefully before choosing the model that’s best for you. (Ask for references to people who are using one.)

The important thing is to plan for the extra heat load from the very start, do the research, and find a contractor who will work with you to choose the best solution in your particular situation.

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