Healthy Home Heating

Let’s review a few of the more common home heating options from the perspective of health and sustainability.

Do you remember Physics 101?  Knowledge of the three modes of heat transfer—convection, conduction and radiation—will help you understand why certain heating systems are more desirable than others.  Convection is heat transfer through fluids, in our case the fluid is the air in our homes.  Hot air rises. Air currents are a natural result of this phenomenon.  Conduction is heat transfer through solids.  When we put our hand on a hot cup of tea or cuddle up with a loved one, we experience conduction.  Radiant heat is the energy that comes from the vibrations of atoms.  It is a form of electromagnetic radiation called infrared.  This is the warmth we feel from the sun, a blazing fire or old-fashioned radiators.

The most commonly used system right now is a forced-air furnace.  There is a heat source, usually the combustion of gas or oil, sometimes wood or coal, or even an electric coil; and a blower fan forcing the warmed air through a distribution system of metal ductwork.  While this system is often the least expensive heating option to install, it scores the lowest on the green building/healthy home checklist.  The forced air is heat transfer by convection.  The blower fan moves a large volume of air to get the heat distributed.  The on and off cycling of forced-air systems and the nature of convection heat results in uneven heating throughout the home.  Metal ductwork accumulates dust and other toxins that circulate into the air.  Maintaining a highly efficient air filter is a must for better air quality.  In low humidity situations, which is often the case in wintertime, static electricity build up is a by-product of forced air through metal ductwork.  Indoor air pollutants like dust, dust mites, animal dander, mold and VOC’s from synthetic building materials and cleaning supplies, become airborne when there is static electricity buildup,  hence the increase of respiratory irritations during the heating months.   Furnaces must have sealed combustion to avoid the entry of combustion by-products into the air stream.

Radiant heating systems are much more comfortable and have lower operating costs, though often higher installation costs.  Old fashioned radiators, baseboard and in-floor radiant heat are some examples of these systems.  An independent ventilation system like an air heat exchanger, heat recovery ventilator (HRV), or passive vents like trickle ventilators, should be considered to introduce a continuous supply of fresh filtered air.   Indoor plants can also help to filter the air and provide needed oxygen.

Electric heat is attractive because it appears clean and quiet.  However, electric heat systems will fry dust and create elevated electromagnetic fields.  They are also much costlier to operate.

Heat pumps, or geothermal systems, are not as efficient when temperatures are below 30 degrees.  They also rely on electricity and freon, which is an atmospheric ozone depletor.  The theory behind extracting heat from groundwater or the earth is good, however, the technological requirements have a cost.

Because of an abundance of firewood in our area of the state, woodstoves are a popular form of radiant heat.  Wood stoves can be messy to operate.  Most of the heat escapes up the smokestack and more than 200 toxic by-products of combustion can be introduced into the home air.  A well-maintained chimney and an airtight stove are important.

A better way of heating with wood is a masonry heater.  Because of the large masonry thermal mass and the downdraft contra-flow flue system, the fire burns hot enough of burn off many combustion gasses and is so much cleaner.  Most of the heat is stored in the masonry mass and then radiated into the home instead of up and out the chimney.  With so much retained heat, only one or two short, hot fires a day are necessary, so they use very little fuel.  Initial installation costs, however, are much higher than for a woodstove, but comparable to a masonry fireplace.

Passive solar heating is one of the simplest and cheapest forms of radiant heat.  Heat from the sun passes through window openings and is stored in building materials with high thermal mass capacity like concrete, brick, stone and water.  This stored heat is then re-radiated into the space.  Because this system is weather dependent, an auxiliary heating source is needed during extended cloudy weather.  Design elements like solar orientation, thermal mass to glazing ratio and nighttime glazing insulation need to be incorporated into the architecture to fully utilize this misunderstood and underused resource.

Choosing a new heating system or retrofitting an existing one is much like addressing the other components in our buildings.  There are choices, compromises and challenges that require some thought and research.  Wherever you find yourself this winter, I hope you have a warm and healthy home and heart.