In Maine, most homes have an oil-fired furnace or boiler. However, there are still some electrically heated homes in the area and I occasionally see a relatively new gas-fired furnace. A popular item lately is the direct venting kerosene or gas space heater. There are also still some wood stoves installed in many homes. Central electric furnaces are rarely found here.

While your home inspector is taking a look around the site before the home inspection, he should look for fuel tanks. If there are no fuel tanks outside, sometimes he will be able to tell approximately where an inside fuel oil storage tank is by the location of fill and vent pipes.

As your home inspector inspects each room, he should be looking for a heat source. If there is circulating hot water or steam heat, the heat source will likely be a baseboard unit, convector unit, or cast iron radiator. If there is forced warm air heat, he will be looking for registers. The warm air registers should be checked by lifting out the grate and looking down into the duct.

As your home inspector works through the interior of the house, he should note the location and setting of all of the thermostats found. Later on, depending upon the result of the inspection of the central heating system boiler or furnace, your home inspector will want to come back and test the heating system by turning all of the thermostats up and seeing if all of the heat sources work.If the house has a central heating system, before you turn up the thermostats, check the physical condition of the boiler or furnace.

The central heating system boiler or furnace is usually located in the basement but occasionally, in a house with a slab foundation for example, it will be on the first floor.

One of the most important items your home inspector should check in the house is the oil burner flue connector pipe. Are there any rust holes? How about the connection into the chimney flue? Is it a tight fit or are there gaps around the pipe connection? Is there a wood stove connected to the same flue?

What about flue connector clearance to combustibles? Is it at least ten inches? In one older house, I found a oil burner flue connector pipe that penetrated the first floor and ran through a closet under a stair on its way into the chimney. The pipe was two or three inches from the stair structure and in contact with the floorboards!

Your home inspector should open up the flue cleanout access door and check for accumulated soot and cinders in the bottom of the flue. If fumes and smoke leak out when the oil burner is first turned on, then there is insufficient chimney draft, the chimney flue is obstructed, or there are openings in the flue connector pipe and the oil burner should be turned off immediately. At this point, depending upon the problem, your home inspector should recommend that a heating system specialist, chimney flue cleaning service, and/or chimney masonry contractor be brought in to make further investigations.

Another item your home inspector should check is the safety heat switch. These are usually found attached to the floor structure above the oil burner facing down. However, on older or homeowner installed furnaces, I occasionally find no heat switch. Sometimes the heat switch is installed on its side so it cannot work properly. Occasionally, I find the heat switch located too far from the oil burner to work properly.

The emergency shut-off switch should be checked. The emergency switch should be located at the top of the basement stair and clearly labeled with a red switch cover. If the oil burner is located on the first floor, the emergency switch should be located near the door into the boiler room. Occasionally, there is a second emergency switch mounted near the oil burner.

The copper heating oil line between the fuel storage tank and the oil burner should be protected inside a secondary containment sleeve.

On boilers, there should be relief valves installed with pipe extensions directing the vent discharge vertically down. There should be a second extended vent relief valve for a tankless water heater if one exists.

While the furnace is operating, try to determine which registers are for supply and which are for cold air return. Keep an eye out in closets for ducts and heat pipes.

In electrically heated homes, you are likely to find a thermostat and heater in every room. The first thing to do after entering an electrically heated room is note the thermostat setting and turn it up. After a few seconds, if you don't hear sounds of expansion coming from the baseboard unit or if you don't feel heat rising from it, make a mental note to check the electric heat breakers later on during your inspection of the main panel. Return the thermostat to its original setting.

If a gas or kerosene space heater is the primary source of heat in the house, your home inspector should check the heat exchanger for leaks or recommend that a qualified licensed specialist do the same.

Every once in a while, you will find portable or permanently installed unvented gas heaters in a home or shop. Because these heaters vent combustion product fumes into the house, they are unsafe and should not be used in occupied dwellings. For more information, read this article by Lance O'Hearn.

Your home inspector should carefully inspect wood and coal stove installations. A significant number of wood stoves are installed by owners who are not aware of proper safety clearances. To my knowledge, the clearance between solid fuel burning equipment and single-wall metal flues and combustible surfaces is four feet. However, I frequently find wood mantels, beams, and interior trim much closer than four feet from the stove and stove pipe.

In old houses with old wood stove hookups, I have found single-wall stove pipes in contact with plaster stick lath and wallpaper. Upon removing the stove pipe from the thimble, I have found the lath charred around the opening!

If I find an unsafe wood or coal stove hookup, I recommend that the stove be disconnected immediately.

Some boilers have tankless coils installed for domestic hot water. Performance of tankless heaters is often reduced during very cold weather when space heating loads are highest. Well water characteristics can also influence tankless heater performance. For example, build-up of material inside the tankless coil can reduce domestic hot water heater performance.

The most efficient method of heating domestic hot water with a central heating system boiler is with a separate zone into a heat exchanger coil in a separate storage tank. Of course, the boiler should be designed with excess capacity in order to handle the increased load of domestic hot water along with the space heating load.

During the 1970s, some homeowners installed wood burning furnaces. Your home inspector should check the ducting between the wood burning furnace and the oil burning furnace. Sometimes, the furnaces will be connected in series. If that is the case, then the overall heating efficiency of the oil furnace will be decreased.