Heating Technology Index

Heating and Cooling Equipment Choices

Here is a short glossary/primer regarding your choices in the heating and cooling field. I hope that it is useful!

General Terms

British Thermal Unit (BTU)
The British Thermal Unit is a measure of heat/energy. It is defined as the amount of energy required to heat one pound of water one degree Farenheit. The BTU is used as a term to define the capacity of heating and cooling equipment alike in the US. In the case of air conditioning equipment, it defines the ability of the equipment to move heat out of the home.

One peculiar leftover from the early days of air conditioning in the US is the measure of "tons" of cooling capacity... it refers to the time when people used ice to cool their homes. One tons of ice cooling is equivalent to about 12,000BTUs. Should you need to convert BTUs into kilo-Watt-hours (kWh), simply divide the BTU number by 3412.
Staging refers to the ways in which the output of equipment can be varied.
  • Single-stage equipment can only operate in a binary mode. It is either 100% on or 100% off. Many furnaces and air conditioning systems are single-stage systems. These are the least expensive to manufacture but may present some comfort issues.
  • Multi-stage equipment can vary its output in distinct steps. For example, a two-stage system may be able to operate at 0%, 50% and 100% output. Multistaging equipment is typically justified on the basis of comfort and/or economy. It is also useful when your home has multiple heating and/or cooling zones, as it will allow the heating or cooling system to more closely match the need (and not blast you intermittantly with hot air, for example).
Modulating Equipment
Modulating equipment goes beyond staging by being able to seamlessly vary its output within a certain operating range. This has maximum benefit for economy and comfort alike. Modulating heating or cooling systems are usually sold at a premium relative to less sophisticated equipment, though comfort and economics alike can justify the marginal expense.

Examples of modulating equipment include many condensing gas boilers, which can vary their gas valves' and electrical blower turn-down ratio. A boiler with a 5:1 turndown ratio can vary it's output from 100% to 20%, for example. On the air-side of the business, Electrically-Commutated-Motors (ECM) allow your home to receive just the right amount of airflow to keep you comfortable.

Heating-related equipment

Condensing Equipment
(more to come)
Air-based heating systems account for 93% of all heating systems installed in the USA. They preominantly use natural gas or propane as a fuel and are usually the least expensive heating system to install. There are several general categories to choose from, including single- and multiple-stage burners and/or condensing vs. non-condensing operation.

One reason that furnaces are so popular in the US is that they allow the easy combination of air conditioning and heating in one system. If you go this route, pay careful attention to ensure that the operation in both modes of operation will work well.

To maximize comfort and minimize temperature variations, look for an install that features air supplies and returns in every room, so that you do not have to rely on room doors being open or undercut in order for the system to function well. Multiple-speed fans, staging furnaces, zoning systems, and balancing dampers will go a long way to minimizing operating costs and maximizing comfort.

As with all heating systems, furnaces benefit from annual inspections/cleanings by a professional. A clean furnace will run more efficiently and will represent less of a fire hazard than a dirty one, so change filters as often as needed to keep the furnace happy. The frequency with which to change the filter will depend on the dustiness of your home, pets, and environmental conditions. See the manual of your furnace for specific guidance on when to change the filter.
Boilers use water and radiators instead of air and ducts to warm your home. So-called hydronic boilers come in a couple of different configurations that can be broken down in two major categories:
  • Steam Boilers heat water until it changes phase and turns into steam. It then travels through steel pipes up to radiators in your home. Steam systems usually do not require pumps and can come in "one pipe" and "two pipe" versions. In the US, steam systems are quite common in the Northeast.
  • Hot water boilers use warm water and a number of different emitters to heat your home, ranging from baseboard to radiant floor heating. Some hot water boilers even heat coils in your air-conditioning system, a hybrid approach called hydro-air.
You can learn more about boilers at heatinghelp.com