Passive Solar Heating

Passive solar heating is a design approach rather than an actual heating system. Windows are placed on the south-facing side of the building, at a scale equivalent to 10-30 percent of the floor area. In the winter, all sun enters and heats the room, and in the summer, shading blocks summer sun which reduces cooling needs. Passive solar design is not enough alone, but it can reduce the load on heating systems. Computer modeling is available to calculate the ideal ideal passive solar design based on latitude and climate. Window glazing must be carefully selected. It's important to remember that passive solar principles can be used to varying degrees: this is not an not all-or-nothing system.

Solar Hydronic

Components: Solar thermal collector (flat plate or evacuated tube), circulation pump and controls, storage vessel, heat exchanger for delivery system.

Summary: A collector gathers the sun's energy, then is transferred to hydronic fluid, pumped to a storage vessel, and deposited heat via a heat exchanger. Solar energy is stored in a well-insulated tank so it can be used at will. Solar hydronic systems need to be carefully designed to calculate how much heat they can deliver based on climate. These systems can also be used to heat hot water.

Advantages: Very low environmental impacts, great for indoor air quality.

Disadvantages: Systems are very complex, expensive, labor intensive, not accepted by most codes without licensed professional.

Solar Hot Air Heating

Components: Solar thermal collector, ductwork, controls and fans.

Summary: Collectors (glazed or unglazed) collect solar radiation, heating the air in a plenum, which is then ducted into the building. These systems can use fresh air or recirculated indoor air. Most systems are homemade and are moderately difficult to install, but easy to use and maintain.

Advantages: Simple, inexpensive, great indoor air quality.

Disadvantages: Not accepted by most codes, may be accepted as an alternative with a licensed professional and backup system.

Ground Source Heat Pumps (GSHP)

Components: ground loops (two types, below) and circulation pump, heat pump unit with compressor, air or hydronic delivery system, controls as required.

Horizontal Ground Loop: collection loop dug into a depth below frost line or water below ice depth.

Vertical Ground Loop: collection loop placed in vertically drilled wells

Summary: Ground loops collect heat (in winter) or disperse heat (in summer). Btus are gained from additional loop length. Refrigerant collects heat from ground loop fluid, a compressor uses the refrigerant to create or extract heat for the building. These systems need to be designed with a precise heat loss calculation.

Advantages: Some can heat hot water, low GHG emissions if used with renewable energy, easily sourced, accepted in many codes

Disadvantages: Ecosystem disruption for ground loop digging, Uses toxic refrigerants, Expensive, labor intensive, need a licensed installer

Air Source Heat Pumps (ASHP)

Components: Heat pump, heat exchanger/plenum, air or hydronic delivery system, controls.

Summary: A heat pump unit outside uses large fans to move air over a heat exchanger coil, which transfers heat to the refrigerant. Heat is delivered through forced air, and can work in both directions.

Advantages: Low GHG emissions if used with renewable energy, easy maintenance, easy to source.

Disadvantages: Fans are noisy, backup heat source may be required in placed with very cold winters, toxic refrigerants, can be expensive, licensed installer required, accepted in many codes.

Tankless or On-Demand Heaters

Components: Combustion chamber, exhaust chimney, direct vent intake and exhaust, circulation pump, relief valve/expansion take/air bleeder as required, controls.

Summary: Similar to direct heat boilers, but the heat exchanger can heat a small amount of water quickly. Environmental impacts depend on fuel source, but are generally high.

Advantages: Moderate costs, easy to source, accepted in all codes.

Disadvantages: Install requires licensed professional, combustion can have negative impacts on indoor air quality.

Masonry Heaters

Components: Burn chamber and ash pan, masonry chimney, masonry shroud, air inlet and controls, cooking oven space, water heating coil or tank

Summary: A freestanding unit placed centrally in home contains a burn chamber for fire to be lit. Exhaust gasses travel through a winding masonry chimney providing additional heating opportunities. Fires need to be timed well to keep unit at optimal temperature range. Environmental impacts are low- these heaters make very efficient use of wood fuel.

Advantages: Low environmental impacts, very durable.

Disadvantages: Difficult insulation, must be fired on schedule, not accepted in any codes, dust and smoke from loading chamber.