There are many different types of heating systems available today. There are also combination units such as wood/gas, wood/electric, oil/electric, oil/wood, etc.
In Ontario, forced air gas furnaces are the most common. These heating systems also come in varying efficiencies including conventional (naturally aspirated), mid and high.
Some Common Types of Heating Systems
Forced Air — system makes heat by clean combustion of gas or oil (electric used also), distributed by a blower, through supply and return ducts.
Steam — system makes steam in oil or gas boiler, circulates through loops of pipes to distribute heat to various zones.
Hot Water — system heats water in gas or oil boiler, circulates heat through insulated pipes to room radiators, condensed in radiator, giving up its heat in vaporization, condensed water then runs back to boiler for re-heating.
Radiant — system makes heat with electric resistant baseboards and radiant ceiling panels. Other forms of radiant heat include hot water heat in the floor or ceiling.
Venting & Flue Pipes – Venting is required on heating systems to exhaust combustion gases from such fuels as gas and oil. There are different methods of accomplishing this with varying types of flue pipes. It is these pipes that vent harmful combustion gases outside. Different metal flue pipes are used in different applications. As a result, each has a specific distance it must be from combustible products. Clay and metal chimney liners are also used within masonry chimneys. Even in induced draft furnaces (e.g. mid-efficiency) flue gases are about 300 F.
In the past, conventional furnace were vented by keeping exhaust gases hot enough that condensation does not form thereby damaging chimneys, flues, or worse yet, the heat exchanger. Condensing furnaces (e.g. high-efficiency units), where exhaust gases are cooler (about 100 F to 150 F) thereby producing condensation in the process, can vent through an exterior wall using a “plastic” vent pipe and induced draft fan. This condensation is somewhat acidic and would likely corrode conventional heat exchangers over time. Now, stainless steel heat exchangers are used to combat this however it can increase the cost of the unit. As considerable condensate can collect (about a litre during a half hour of operation) it is important to make sure it is drained.
High-efficiency units can get their combustion air supply from within the home however due to indoor air pollutants it is recommended that the supply come from outside. When this is done the system is referred to as a direct vent or sealed (from indoor air) combustion units.
Burners – With gas the flame colour should be blue and with oil the flame should be orange. A yellow to orange coloured gas flame may indicate a cracked heat exchanger, improper combustion, poor flame adjustment, etc. Dust particles in the air can cause a blue gas flame to turn yellow. If the humidifier is running and water in the area is soft the gas flame could be orange.
Many of the conventional units in use today have pilot lights. Over time these units are being replaced by electronic ignition.
Heat Exchanger – A metal chamber, called a heat exchanger, is the “heart” of the furnace. It separates air being heated from the burning fuel. Most, if not all, of the heat exchanger is not visible during a home inspection. Typically, dismantling of the furnace is required for inspection.
A heat exchanger that indicates signs, or raises suspicions, of failure may have certain health/safety concerns such as allowing Carbon Monoxide (CO) to enter the home. Although heat exchanger replacement may be possible in rare cases, the more common and costly approach is to replace the furnace itself.
Draft Units – Oil furnaces have draft inducing elements as well as some gas units. Oil units have this “barometric damper” on or near the flue pipe. Gas units usually have a draft hood at the point the flue exits the furnace housing.
There should be no outward flow of hot exhaust gases from these drafts, if so, dangerous gases are likely not being properly vented.
Supply & Return Ducts – Forced air systems must be balanced in order to work. As the system must be able to supply heat then it must have return cold air ducts from which it can draw air. As a result, supply air then must be balanced with incoming air. Too much supply and little return air (or vice versa) will tax the system yielding an overworked and inefficient system. Moreover, comfort levels must be maximized which means that room air circulation and balancing of ducts (using dampers) to each room is important as well. A rule of thumb is that the return air grill must be at least as large as the supply register.
Cold air return ducts should not be located within 6 feet of the furnace to prevent back drafting.
Safety Controls – No heating system is complete with out safety controls. Some heating units have “sniffers” to detect harmful gases.
Forced Air – Aside from the thermostat there are two basic controls. 1) A high temperature limit switch (measured by air temperature). 2) A fan control (which lowers the temperature by blowing off built-up warm air in the heat exchanger).
Steam – Aside from the low water cut-off and a water-level gauge, there are two basic controls. A high temperature limit switch (shuts down burner when pressure in boiler exceeds a predetermined setting) and pressure relief valve (usually discharges at around 15 psi).
Hot Water – As with a Steam system the relief valve will discharge water at a predetermined pressure (usually about 30 psi).
Fuel Controls – Both gas and oil units have controls to stop the flow of fuel to the burner. Gas units use a thermocouple that closes the flow of gas. Oil units should have firomatic safety valves, which shut down if there is a system malfunction (should be three — one on the fuel tank, one on the oil burner, and one over the unit itself).
Blower/Blower motor – An often over looked area is the high velocity fan (blower). It can account for about 30% of the operating efficiency of a conventional forced air system. If dirty, the blower and motor will have to work longer/harder. If the blower is belt driven it should be checked for tightness, alignment, and, wear.
Filters – Used with forced air systems, can be disposable, reusable, or, permanent.
Disposable filters (least expensive) should be replaced often (monthly) during heating and cooling seasons (if central cooling system used). For the most part, those one inch thick disposal filters don’t do much to filter the air.
Reusable filters (higher one-time cost than disposable) must be cleaned often (monthly) during the same period.
Permanent filters (most expensive) include electronic air cleaners. In order for them to work properly they should be cleaned every time they get dirty which could be weekly or monthly.
Other filters include HEPA (High Efficiency Particulate Air) which do a great job removing most harmful indoor air pollutants. Certain wet style filters (a metal mesh filter and spray-on adhesive) work well to trap air borne particles too. There are also charcoal pre-filters that can be used as well to remove, for example, odours in the indoor air.
Other Types of Heating & Fuels – There are literally hundreds of different types of heating systems including space or portable heaters, fireplaces, wood stoves, heat pumps, and solar heating.
There are varying fuels types also which we haven’t talked about. They include propane and solid fuels like wood, coal, and, pellets.
Thermostats – are used for calling for heat from the system. Depending on the system configuration, multiple thermostats can be used for “zone” control and can be an effective and efficient way to heat your home.
The location of the thermostat also plays a crucial role in calling for heat. Locating a thermostat on an outside wall or next to a fireplace will yield poor results.
Standard thermostats should be checked against another thermometer for accuracy, kept clean and free of debris. It must also be level so that the mercury bulb inside it can call for heat appropriately.
Programmable thermostats can assist with reducing energy consumption by ensuring the temperature is set back, for example, when you are out or heat is not required.
Advantages & Disadvantages of Heating System Types
- low installation & maintenance
- cool air is warmed quickly
- can use duct work to cool, humidify, dehumidify, clean
- components don’t freeze in cold weather
- repairs costs low (no plumber required)
- filters and ducts require cleaning
- space required around furnace for servicing, bulky, hard to conceal ducts
- faulty heat exchanger can cause combustion products to enter home
- balancing system/air flow to rooms difficult
- less heat the further you are from source, unit can be noisy
- low maintenance, quiet, clean operation
- takes up less space than forced air systems
- even temperature distribution, can thermostat/zone each room
- convectors remain warm for considerable time after heated up
- can be used with many fuel systems
- more expensive installation than forced air
- hot water responds slowly to cool house
- expensive to add cooling, humidify air, replace pump
- water pipes can corrode, leak, pipes can be noisy when expand/contract
- baseboard convectors can get in the way
- no chimney required as no combustion products
- inexpensive to install, freedom from pipes and ducts
- takes up little space, quiet, low maintenance
- can thermostat/zone each room
- highest operating cost, larger main electrical supply required
- poorer thermostats can result in higher heating bills
- slower to respond to sudden temperature drops
- expensive to add cooling, humidify air
- efficient in small spaces
- can thermostat/zone each room
- takes little space as no mechanical room, ducts, baseboards
- room contents warmed by radiant
- repair bills can be high if panels damaged
- can be difficult to add ceiling fixtures
- hot water radiant often more expensive than electric
- slow to respond
- special ceiling, floor or wall preparations required