The Effect of Heating on the Indoor Environment

Residential Heating Systems

Residential structures, like single-family homes, typically use systems designed for smaller, more uniform spaces. The most common types are:

• Furnaces: The most popular type of heating system in the US. A furnace heats air by burning a fuel like natural gas, propane, or heating oil, or by using an electric heating element. A blower fan then pushes this heated air through a system of ducts and vents to heat the entire house. These are often part of a forced-air system that also uses the same ductwork for central air conditioning.

• Boilers: Unlike furnaces, which heat air, a boiler heats water. This hot water or steam is then circulated through pipes to radiators, baseboard heaters, or a radiant floor system to warm the space. This is a hydronic system, meaning it uses water to transfer heat. Because it doesn't move air with a blower fan, it tends to be quieter and doesn't circulate dust or allergens as much as a forced-air system.

• Heat Pumps: A highly efficient, all-in-one system that can provide both heating and cooling. In winter, a heat pump works like a refrigerator in reverse. It extracts existing heat from the outside air (even in very cold temperatures) and transfers it inside the home. In summer, it reverses the process, removing heat from inside and moving it outside. Heat pumps are an excellent alternative to traditional furnaces and air conditioners, especially in moderate climates.

Commercial Heating Systems

Commercial structures, such as office buildings, retail stores, or warehouses, require heating systems with a much larger capacity and more flexible controls to handle varied usage, occupancy, and floor plans. The systems are designed for durability, reliability, and zoning (the ability to heat different parts of the building to different temperatures).

• Commercial Boilers: Similar in principle to residential boilers, but on a much larger scale. They are often found in multi-story buildings and hospitals. They use a central boiler plant to heat water or create steam, which is then distributed to different areas of the building to provide heat through radiators, baseboard heaters, or coils in air handlers.

• Rooftop Units (RTUs): These are a very common commercial HVAC solution. An RTU is a single, self-contained unit that includes all heating, cooling, and ventilation components. As the name suggests, it's mounted on the roof of the building, which saves valuable indoor space. RTUs typically provide heating with a built-in gas furnace or electric coils and distribute conditioned air through a duct system. They are ideal for large, single-story buildings like retail stores or warehouses.

• Variable Refrigerant Flow (VRF) Systems: This is a more advanced and highly efficient system that is gaining popularity in commercial buildings. VRF systems use a single outdoor unit connected to multiple indoor units, each with its own control. This allows for zoning, where different parts of the building can be heated and cooled simultaneously, according to the specific needs of each zone. They use refrigerant to transfer heat directly between the outdoor and indoor units, which makes them very energy-efficient

Heating and Humidity

Heating systems, such as furnaces and boilers, work by adding sensible heat to the air. Sensible heat is the energy that you can measure with a thermometer; it raises the temperature of the air but doesn't change its moisture content (latent heat).

When cold air from outside (which has a low amount of moisture) leaks into a home and is then heated, its relative humidity drops significantly. This is because warmer air can hold more water vapor, so even with the same amount of moisture, the air feels drier. This is why many people use humidifiers during the winter—to add moisture back into the air to counteract this effect.

Unlike heating, air conditioning systems remove both sensible heat (cooling the air) and latent heat (removing moisture). They do this by condensing water vapor on their cold evaporator coils, which is why you see a drain line on an A/C unit.

The Importance of the Building Envelope

The second part of your statement is also spot on. The amount of energy needed to heat a property is directly determined by the effectiveness of its building envelope—that is, the insulation and air tightness of its walls, roof, floors, windows, and doors.

Think of your house as a thermos. A well-insulated, airtight thermos keeps the hot liquid inside hot for a long time because it slows the transfer of heat from the inside to the outside. In the same way, a well-insulated, airtight home keeps the heat inside and the cold air outside.

• Insulation resists the transfer of heat through conduction. A higher R-value (a measure of thermal resistance) means the insulation is better at keeping heat from passing through the walls and roof.

• Air tightness prevents heat loss through air leaks (also known as air infiltration). Unwanted drafts and gaps around windows and doors can account for a significant portion of a home's heat loss, regardless of how much insulation it has.

By improving a home's insulation and sealing air leaks, you reduce the amount of work your heating system has to do to maintain a comfortable temperature, which in turn saves you money on energy bills.