Home Heating Overview

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Heating our homes is a complex problem as there are three major challenges for a home heating system. First, the heating system needs to be able to safely convert some form of convenient energy into heat. Second, that heat needs to be distributed around the home as desired by the home occupants. Third, the system has to be as energy efficient as possible to be affordable.

Heating Energy Sources

Common residential systems for home heating get energy from:

  • Combustion - The combustion process means we are burning up a resource in order to extract heat. The most common form of combustion for heating homes today is natural gas however propane, heating oil, or organic products like wood can be burned to create heat. The combustion process has inherent safety risks as exhaust gasses need to be safely managed from the home. Natural gas has become the most common energy source and as it is delivered to homes with a constant supply it does not require regular replenishment like heating oil deliveries or wood stoking.
  • Electricity - Electricity is conveniently delivered to our homes and is an excellent source of energy for heat. The advantage of electricity is it is 'clean' in the home to use and can be generated locally where needed in the home. The downside is it has typically been more expensive to heat homes with electricity, especially in markets with time-of-day pricing. There is also an argument that electricity is less efficient than combustion because of losses in energy with the creation and distribution of supply.
  • Heat Pumps (air-to-air) - More and more homes are taking advantage of 'heat pumps' to lower heating energy costs. Common heat pumps are able to extract heating energy from outdoor 'cold' air through some high-school physics involving the compression of gasses and liquids. Air-to-air heat pumps require electricity to power an outdoor compressor unit where the energy transfer between the outdoor air and the heat pump system takes place. The energy efficiency of this system drops the colder the air becomes outside which is why heat pumps still need a backup heat source (typically a furnace) for when the air is too cold to transfer any useful heat.
  • Geothermal Heat Pump (ground-loop) - Geothermal heat pumps use the same physics as air-to-air systems but instead of an outside air transfer, they use a loop of liquid which transfer energy from the consistent temperature of the earth with loops of piping buried in deep shafts. The advantage of the geothermal loop is that the earth temperature is always suitable for energy transfer (unlike outdoor air temperatures) and the energy is effectively unlimited. The down side is the expense of installation which can be very substantial and not all building sites can drill to the depths needed for the system to operate.

Converting Energy to Distributable Heat

Heating equipment in the home has to have a dual role. First, it needs to be able to convert the energy source into actual heat, and second, it needs to be able to move the heat to where the occupants of the home need it. There are many methods of accomplishing this with the most common being:

  • Forced Air Furnaces - Forced air furnaces commonly burn natural gas to generate heat although they can also use electric heating elements. This heat energy is then distributed through the home using a 'blower' which forces heated air from the furnace through the home. The advantages are this system are that the equipment and install costs are relatively low and the system is relatively efficient. The disadvantages are that the furnace heats the whole home at one time meaning there is little ability to direct heat to where it is needed in the home at any point in time. There is also a limit to how far a furnace blower can throw a supply of warm air in a home.
    • Heat Pump - Most heat pumps 'borrow' the blower fan system from a common furnace in order to facilitate the heat transfer from outside. As air moves with the furnace blower, heat from the heat pump is transferred using a radiator in the furnace system into the forced air flow. When the heat pump cannot generate enough heat to satisfy occupants, the heat pump shuts down and the conventional furnace system will begin burning natural gas for a heat source. Heat levels from heat pumps are much lower than from the natural gas burners, as a result, heat levels at the furnace air vents will be cooler with heat pump operation and will run much longer in order to transfer the total heat levels needed.
  • Hot Water Boilers - Forced air furnaces use air to move heat through the building. Hot water boilers use water in pipes to distribute the heat energy. Natural gas burners heat water centrally at the boiler and a serious of pumps, zones, and valves control the flow of hot heating water in the home. Heat is released in each room through radiators or in-floor heating. The advantages of hot water heating are there is no draft of forced air, the heat can be distributed further from combustion in the piping, and individual zones can allow greater heat control per room (or zone). The disadvantages are increased complexity in the installation and equipment costs, higher risks of failure if something goes wrong with the system, and a much longer cycle to provide heat. While hot water for heating cannot be directly mixed with domestic hot water for our taps, there are methods of distributing heat between a heating boiler and a hot water tank system.
  • Steam Heat Systems - Steam and water heat systems share some characteristics in the conversion of energy to heat at a central boiler but the method of delivering the energy is very different. Steam takes advantage of another high-school physics concept called the latent heat of vaporization to distribute the heat energy to each room or zone as latent heat in the steam itself. When the steam cools at the in-room radiators into water, it releases the latent energy as local heat. These systems are extremely rare in residential homes and are more likely found in commercial heating applications including some condos.
  • Fireplaces - Fireplaces are not commonly used to heat entire homes but they can be an efficient method to add localized heat to a room. Fireplaces can burn natural gas, be wood burning, or can use electric heating elements. Some fireplaces use fans to help circulate heat in rooms but units without fans are still quite efficient thanks to radiant heat transfer.
  • Electric Heating - Heat energy can be centrally created and distributed (like in a forced air furnace) or it can be locally created as needed in each room. The most common form of electric heating is baseboard heaters which are controlled individually in each room by separate thermostats. There are also in-floor electric heating systems available as well as local room electric furnaces which use a fan to help distribute heat energy. The advantages of electric heat is it can be locally controlled for each area in the home, it is quick to respond to operator requests for heat, and it is relatively easy and inexpensive to install. The downside is the cost of heating with electricity is typically higher than with other forms of energy.

Energy Efficiency

While energy is largely free on earth in the form of sunshine, the force of gravity, and wind, the ability to control that energy for our convent use has always been a challenge. This ability to control, predict, and sell energy is why companies have invested billions of dollars in extracting oil and gas and the creation of hydro-electric power dams and coal burning power plants. Home heating costs are a reality for home owners and their desire to keep energy costs low have driven a lot of improvements in energy efficiency.

Governments have also been very influential in increasing energy efficiency. A by-product of our desire for controlled energy has been the combustion of non-renewable resources which has had impacts on our environment and health. To protect population health long term and to help plan for the future of energy for society, Governments at all levels have been exerting a lot of influence on energy discovery, distribution, and use of energy. As home heating is a major user of energy, Governments have been very influential in increasing home heating energy efficiency.

Common home heating systems have improved in energy efficiency significantly in the last few decades:

  • Heat Pumps - Geothermal ground loop heat pumps are the most efficient system for heating homes as the earths core temperature remains consistent no matter the weather outside. Unfortunately, the initial start up costs of geothermal heat pumps are very restrictive despite government attempts to provide financial incentives for installation. Air-to-air heat pumps are significantly less expensive and operate very well in moderate outdoor temperatures over 8 Celsius but still provide energy efficiency all the way to about -8 Celsius.
  • Natural Gas Furnaces - Natural gas is a relatively 'clean' burning fuel. While it still produces some greenhouse gasses, it is cleaner than heating oil or wood burning systems. Changes in the design of natural gas furnaces have seen the elimination of standing pilot lights and improved heat transfer so the annual fuel usage efficiency (AFUE) rating now approach 97% (meaning $97 of every $100 in gas goes to heating the home). Older furnace systems were as low as 60-70% efficient. The newest technology in efficiency are 'condensing' furnaces which actually recapture lost energy in the combustion process that used to go out of our home as steam. Forced air furnaces are easy to control with programable thermostats and are quick to cycle our home air temperatures when occupied which increases efficiency also. Unfortunately, they are inefficient at delivering heat just to the desired rooms that may be occupied.
  • Hot Water Boilers - Hot water boilers have seen efficiencies in the combustion of natural gas much like forced air furnaces. The best hot water boiler AFUE ratings are slightly lower than the best forced air furnaces at about 90% ($90 in heat for every $100 in fuel purchased) however water heating systems can be used in large homes where heating with forced air is not possible. Hot water systems do gain some efficiency in that there can be multiple zones of heating in a home. Unfortunately, hot water systems have a large cycle time to provide heat (or cool down) which reduces the efficiency of turning down the temperature during low home usage in the day.
  • Electric Heating - Electric heating is a little more difficult to explain for energy efficiency as inside the home, electric heating is nearly 100% efficient because there is no loss of energy in a combustion process. The additional parameters include the original energy source for the electricity and the losses in energy delivering the electricity to your home. While in British Columbia we like to think our electricity comes from 'clean' hydro-electricity, the reality is we are connected to the North American electric grid and we consume more power than we generate. This means that our net power is no cleaner than anyone else in North America. Electricity in North America is largely produced from burning natural resources, largely coal. The total efficiency of the electric grid is close to 40% when comparing potential energy of raw resources and losses in distribution to our homes. This is also why electricity is such an expensive source of heating our homes as we lose the efficiency of the original fuel source before it reaches our home. Electric heating however does have benefits in that we can control heat to each individual room and it can be used in spaces where it is not possible or safe to use local combustion.
  • Balancing Heating Systems - No matter if you heat with electricity, hot water, or forced air, a heating system needs to be correctly balanced to deliver the most efficient heat possible. Systems that are oversized will waste unneeded heat energy and for some systems the stress of cycling on and off too often will cause premature break downs. Undersized systems will leave occupants uncomfortable and may force equipment to wear down prematurely. Balancing heating systems is a complex process that should be done during the planning stages of new home construction. Balancing existing home heating systems can be very difficult and disruptive. Home owners need to be aware during major renovations of their impacts to a potentially well balanced heating system.

Home Inspection Thoughts

Heating our homes is a complex task that is best left to the processionals to plan during new home construction. As home inspectors, our role is to ensure that installed heating systems function correctly and to provide some education to home inspection clients on the installed equipment and options available to them for the future. Ultimately, it is our goal to help protect and inform our clients so they can make good decisions that will keep them safe and warm.

By James Bell - Owner/Operator of Solid State Inspections Inc.