Heating and Cooling Equipment

According to the State of Illinois standard operating procedures for home inspections, when inspecting the heating and cooling systems of the house the report must “describe the energy source, the heating equipment, and the heating method by their distinguishing characteristics”, and must “describe the energy source and the cooling method by their distinguishing characteristics”.

Here are some details to help you understand what the “distinguishing characteristics” of this equipment really means.

HEATING EQUIPMENT

A furnace is an appliance that heats air, and then sends that air into the dwelling.  A boiler is an appliance that heats water, and then sends that water or steam through pipes to the various rooms of the dwelling.  Most boilers don’t actually boil the water, they just heat it up to somewhere between about 120 °F and 180 °F.  Some boilers, called “steam boilers”, actually boil the water and create steam.

HOW IS THE HEAT CREATED?

There are several ways to create this heat:

• Burning natural gas – “gas-fired”
• Burning fuel oil – “oil-fired”
• Electric resistance – Electricity is converted directly to heat energy. “electric resistance”
• Electric heat pump – Electricity is used to power a device that transfers heat from a cool space to a warm space, making the cool space cooler and the warm space warmer. “electric heat pump”

HOW IS THE HEAT SENT THROUGHOUT THE HOUSE?

Furnace – Once the air is heated by the furnace it needs to be sent throughout the house.  Most homes use a “forced air” furnace.  This includes a blower fan to blow the heated air through ducts and into the various rooms of the house.

Sometimes a furnace only heats the room it’s in.  This is usually called a “room furnace” or “wall furnace”.  Sometimes there’s a small blower fan to help things along.  And sometimes the heated air just drifts naturally into the room, although this is quite rare today.

Many many years ago furnaces didn’t have any kind of blower fan and they just heated the air and let that air rise up through the ducts by natural buoyancy.  This kind of system is exceptionally rare today.

Boiler – Once heated, the warm water or steam is sent through pipes to various rooms of the house and to either radiators or convectors.  Hot water systems use one or more electric circulator pumps to move the water.  Steam systems don’t use pumps.  The steam has enough of a pressure difference compared to the surrounding air to fly through the pipes without any additional help.

Radiators are the big things in rooms that we normally associate with hot water or steam heat, although many modern radiators are quite thin and flush to the wall.  They work primarily by radiating heat out into the room.  Radiation is the same process by which heat energy from the sun reaches us.

Convectors are installed along baseboards down low against a wall.  They work primarily by having cool room air be drawn in along the bottom and get heated by the warm water.  That now-warm air rises up by natural buoyancy and into the room.  Convection is the term that describes heat transfer by the movement of a fluid due to differences in temperature and density.  (Air is a fluid.  It’s not a liquid, but it is a fluid.)

Many many years ago hot water systems didn’t use any circulator pumps.  Just like air, warm water will rise.  The boiler heated the water and it rose up and throughout the house while the colder water dropped back to the boiler to be reheated.  These systems are exceptionally rare today.  However, if you have an older house and some of your boiler pipes are galvanized steel in the range of 2.5-3 inches outside diameter then your system was originally a gravity system – no circulator pump.

HOW ARE THE COMBUSTION GASES VENTED TO THE OUTSIDE?

A furnace or a boiler that burns natural gas or oil needs a vent system to get the products of combustion out of the house.  The vent system is described by its material and by the pressure it creates.

The vent might be metal (probably galvanized steel but maybe stainless steel), or PVC plastic, or it might be a brick chimney lined only with clay tiles.  Sometimes, in houses of a particular vintage, the vent might be made of a fiber cement product that probably contains asbestos.

Many many years ago some gas-fired heaters didn’t use any vent at all.  This is a terrible idea.  Don’t use an appliance like this.

Some appliances use a fan to create pressure to force the flue gases out through the vent.  These are called “forced draft” appliances.  With this type of vent the joints between individual pieces of vent pipe must be sealed airtight, to prevent those high-pressure flue gases from leaking out of the joints.  That’s why PVC is a common material for a “forced draft” appliance – it’s easy to glue the PVC joints together and make them airtight.  These are typically high efficiency appliances.

Most standard efficiency furnaces and some boilers use an “induced draft” vent.  In this case a fan pulls air and natural gas through the combustion chamber and through the heat exchanger, and then after being burned the flue gases rise up through the vent by natural buoyancy.

Most boilers and most water heaters use a “natural draft” vent.  There’s no fan in the system and all of the flue gases just rise up and out through the vent by natural buoyancy.  Most very old furnaces also operated as a “natural draft” appliance.  If your furnace is a “natural draft” appliance then it’s very old.

OTHER HEATING OPTIONS

Electric Resistance – Electric resistance heating using baseboard convectors is quite common.  The heat is generated from electric resistance – electricity is converted directly to heat energy.  They work primarily by having cool room air be drawn in along the bottom and get heated by the electric resistance heating elements.  That now-warm air rises up by natural buoyancy and into the room.

Fan Coil System – A fan coil system is often used in high-rise buildings.  A central plant creates warm and chilled water and pumps that water to a fan coil unit where a fan pulls in room air and blows it over the water pipes and into the room.  A 2-pipe system means that only chilled water or only warm water can be delivered to the fan coil unit – one pipe sends the water to the fan coil unit and one pipe sends it back to the central plant.  By law in most places (and by common sense) the building has to err on the side of providing heat, and must provide heat after a certain day in the fall.  But there might be very warm days in the late fall when you’d like to have cooling but it’s not available because the building has already switched over to heat.

A 4-pipe system means that both chilled water and heated water can be delivered at the same time, so this system is nice during the times of the year when you might not be sure if you’ll need to heat or cool your home.

For more information on fan coil systems see my blog at:

nationshomeinspections.com/fan-coil-units

Heat Pump – A heat pump is an appliance that uses electricity to power a device that transfers heat from a cool space to a warm space, making the cool space cooler and the warm space warmer.  So a heat pump doesn’t actually create heat – it just moves it from one place to another.  A heat pump is often described as an air conditioner that can work in reverse.  That’s not a completely accurate statement but it’s pretty close.

Once the heat is separated from the cold it’s transferred to the air and sent through the dwelling in ducts and into the various rooms.  Or in the summertime the cold air is sent through the ducts.

An air source heat pump takes heat out of the air.  This of course becomes harder as the air gets colder, and eventually it might become necessary for electric resistance heat to be used to keep up with the heating demand.  This electric resistance heat is built into the heat pump and is no different than what you’ll find in an electric furnace or electric baseboard heaters.

A ground source heat pump takes the heat from the ground through buried pipes or deep wells, where temperatures stay fairly moderate even during the coldest winter months.  A ground source heat pump is very efficient.

Packaged Terminal Air Conditioner (PTAC) – A PTAC is a self-contained unit that heats and cools small spaces and is installed through a wall.  These are very common in hotel rooms.  These devices provide both heating and cooling.  (Now might be a good time to mention that at its most basic level the term “air conditioning” does not mean “cooling.”  Air conditioning means to condition the air – to make it hotter if it’s too cold or to make it colder if it’s too hot, and to make it more humid if it’s too dry or to make it dryer if it’s too humid.)

The heating might be done through electric resistance, heat pump, hot water, or steam.  The cooling works through the standard refrigeration cycle.

COOLING EQUIPMENT

A “split system central air conditioner” means a system using the standard refrigeration cycle with a condensing unit outside and an evaporator coil inside (thus the term “split”), along with two refrigerant lines running between them.  Electricity is used to power the system.  Cold air is produced at the inside evaporator coil and is then pushed by a fan through ducts and into the various rooms of the dwelling.  In most cases the blower fan is the same one used by the furnace, although sometimes an air conditioner is a stand-alone type and isn’t integrated with a furnace.

Most air conditioners use standard sized ducts and the air is pushed through them at a standard velocity.  But in some cases, when air conditioning is retrofitted into an existing house, small flexible ducts are used.  These smaller ducts can be snaked through existing construction more easily.  In this case the blower fan moves the air at a higher velocity.  These systems are often called “SpacePak” systems, although SpacePak is just one particular manufacturer of this type of system.  Unico is another big manufacturer of this type of system.

There is really no functional difference between these two types of air conditioners, except that one uses large ducts and moderate air velocity while the other uses small ducts and high air velocity.

A mini-split ductless system uses a single outside condensing unit but multiple inside evaporator coils, with separate refrigerant lines running to each inside coil.  These systems don’t use ducts and each inside unit only cools the room in which it’s installed.  A mini-split system can also be driven by a heat pump and so it might provide both heating and cooling.