By placing your main emphasis on your building envelope, and making good decisions to insulate well, you have just saved yourself some money on your heating system. The better insulated a home, the smaller the heating system that is required.
There are three main types of heating systems, having various efficiencies. Heat pumps are always going to be more efficient (and cheaper to operate) than combustion or electric resistance systems.
The most common types of combustion heating systems involve the burning of oil, wood, natural gas or propane. The heat can be delivered throughout the house (central heating) with pipes or ducts, or emanated from a point source (stove or fireplace). Combustion heating systems are less than 100% efficient because heat is “lost” as it exits via the chimney. Depending on the technology, wood combustion systems are 55% to 75% efficient, and oil is around 85% efficient. Condensing gas systems are the most efficient combustion scenario with efficiencies over 90%.
The most common types of electric resistance heating systems are electric boilers (hot water central heat) and electric baseboard heaters (space heating). Electric resistance heating is considered to be 100% efficient, meaning that one unit of energy (electricity) in will result in the equivalent amount of energy (heat) out. However, in Atlantic Canada, the production of electricity is largely based on fossil fuels, making electric heat somewhat of an environmental concern.
Heat pumps do not create heat directly. They extract heat from an outside “source” using the refrigeration cycle, and deliver it to the inside of your home. The two “sources” of heat for heat pumps are the ambient air (air source) and the ground (ground source). Heat pumps are considered to be much more efficient than Combustion or Electric Resistance systems, with efficiencies of up to 300% (air source) and 500% (ground source). The efficiencies of heat pumps are primarily related to their sources of heat. Air source heat pumps are “victimized” when the outside air falls below a certain temperature. The temperature at which an ASHP begins to lose its ability to gather heat is specific to the manufacturer and model of the equipment.
Air Source Heat Pumps
Air Source Heat Pumps (ASHP’s) come in two flavours; fully ducted systems, and ductless systems (also called mini split heat pumps). A fully ducted system distributes heat like a more familiar oil forced hot air system, in that the heat pump gathers its heat from the outside and dispenses it into ductwork which distributes it around your house. A mini split has no ductwork and a wall mounted unit radiates heat from a point source.
Most common ASHP’s, be they fully ducted or ductless, are “split” systems, in that they are split into two separate components; an outside coil and an inside coil. The outside coil is responsible for harvesting heat from the outdoors during the heating cycle and dumping heat to the outdoors during the cooling cycle. The inside coil is responsible for dumping heat into the house during the heating cycle, and gathering heat from the house during the cooling cycle.
Like all mechanical equipment, there is a wide range of sizes (heating/cooling capacity) and various qualities (efficiencies) of ASHP’s. Given the advances in ASHP technology, particularly around variable speed compressors, and the fact that the outside air temperature in Atlantic Canada is rarely below -20°C, these systems can be a very energy efficient choice for your new home.
Ground Source Heat Pumps
Ground Source Heat Pumps (GSHP’s), like ASHP’s, have two components, an outside infrastructure to extract heat from the ground, and an inside unit to dump the gathered heat into the house. If area permits, the most cost effective strategy is to employ a ground loop, whereby a continuous loop of piping is buried in the ground within a horizontal trench. The length of the loop depends on the amount of heat needed to heat the house. If the size of the house lot is limited, it might be necessary to take a vertical approach. Wells can be drilled to access ground water, from which heat can be extracted, or for placing a vertical loop of piping containing water that picks up heat from the ground. The number and/or depth of the well(s) depend on the amount of heat needed to heat the house.
The fluid carrying the low grade heat moves into the indoor unit. Using the refrigeration cycle, the low grade heat is upgraded to a higher grade heat which is distributed through the house. A feature of a GSHP is its ability to contribute to the domestic hot water needs of the house using a component of the heat pump called a desuperheater. If a desuperheater is employed, up to 50% of your annual hot water needs can be met.
Heated Floors and Slabs
No one will argue the comfort of a heated floor or slab. However it must be recognized that the advent of heated floors was a response to the symptom of a poorly insulated Building Envelope. Several decades ago, an R20 wall, R40 attic, clear double glass panes and little attention to air sealing were standard practice. As a result, for those wanting to move away from forced hot air, an electric boiler circulating water through the slab was a good option. Since the heat generated was going to find its way outside relatively easily, it would be good to have it right at your feet to start with. If proper attention is paid to the building envelope, including adequate insulation under your basement floor/slab, then you can achieve the desired result of a warm floor without the cost of installing in-floor heat. If the cost of an electric resistance in-floor heating system was split between additional building envelope insulation and the cost of a heat pump, the energy savings would be significant. Having said that, if in-floor heat is in your plans, insulate under your slab to R20, and you will help maximize the energy efficiency of your heating system.