Operating a Heating System
For greater efficiency, don't locate a thermostat near a heat source or cold draft because they can cause a heating system to operate erratically. This includes shading thermostats from direct sunlight. Also, do not turn the thermostat beyond the desired temperature. It will not make the heating system heat your home any faster. It will only waste energy. Residents who duel one another over the thermostat settings, moving it up and down to suit their different comfort levels, cause heating systems to operate erratically and inefficiently.Selecting a Heating System
When selecting a heating system, consider the following three characteristics carefully: the energy efficiency rating, sizing, and the system's components.
Energy Efficiency Rating
The U.S. Federal Trade Commission requires manufacturers to provide an annual fuel utilization efficiency (AFUE) rating on all heating equipment. This rating provides consumers with information about the operating costs of a particular model that is being considered.
Boilers and warm air furnaces available today have an AFUE rating of 78% to 97% compared to heating appliances of the past that had ratings as low as 65%.
An illustration, but not actual data, of how the AFUE ratings compare. A heating appliance that has a 65% AFUE rating will utilize sixty five cents of every dollar of fuel that you purchase. The remainder of the heat 35% is directed to the outdoors via the chimney. A heating appliance that has a 97% AFUE rating will utilize ninety seven cents of every dollar of fuel that you purchase and only 3% is directed outdoors via a plastic pipe.
The initial purchase co
sts of a 97% AFUE heating appliance is greater than a lower AFUE rated appliance but in cold climates the increased costs can be offset in a few years.
Sizing
When selecting a new heating system, it's important that you determine the proper size needed for your home. Bigger is not better. Oversizing causes the heating system to start and stop more frequently, which is less efficient and harder on the components than letting it run for longer cycles. A properly sized heating system will also provide you with better comfort and humidity control than an oversized one.
The capacity of heating systems is measured in Btu (British Thermal Unit) per hour. Correct sizing procedures involve complex calculations, which are best performed by an experienced contractor, who uses sizing methods accepted by the heating industry. Don't employ a contractor who guesses the size of the heating system needed. Rule-of-thumb sizing techniques are generally inaccurate, often resulting in higher than necessary purchase and annual energy costs.
System Components
You and your contractor should discuss options that will help improve your home's comfort and the economy of your heating system. Regarding ducts, for example, it's important to carefully consider their design and materials, as well as the proper amount of space they require. Check your home's blueprints to see if the architect and builder have planned adequate space for ducts and fans. Heating and cooling contractors complain that they often have to squeeze heating and cooling systems into spaces that are too small, resulting in constricted ducts and inadequate airflow.
Installing a New Heating System
A heating systems performance and energy efficiency not only depends on the selection and planning of the equipment but also on careful installation.
Consumers and home builders alike tend to accept the lowest bid for heating and air-conditioning work. This unfortunate choice can often leave a system lacking 10 to 30 percent in the materials and labor necessary to optimize heating system performance. Rather than just accepting the lowest bid, it's best to research the performance records of local contractors, and get involved in the planning and decision-making about your new heating system.
You can avoid most of the common comfort and performance problems from improper installation by following these guidelines:
- Make your home as energy-efficient as you can with proper insulation, energy-efficient windows, and an effective air barrier, etc. Then your contractor can install a smaller heating system with shorter duct lengths.
- Install the ducts inside your home's insulation and air barrier, if possible. Research shows that this strategy is a major energy saver.
- Insulate your ducts to R-8 if they must be located in an attic or crawl space beyond the home's air barrier and insulation.
- Specify that the measured air leakage through your new ducts be less than 10 percent of your system's airflow. Air leakage of 5 percent or less is possible with careful workmanship.
- Tell your contractor that you want a return register in every room.
- Don't use building cavities as ducts. Building-cavity return ducts are notoriously leaky and often cause comfort, energy, and moisture problems.
- Pull on ductwork after installation to make sure it is fastened and sealed well. (Seal duct joints with mastic.)
Maintaining and Servicing
The heating system performance will deteriorate without regular maintenance and service. The difference between the energy consumption of a well-maintained heating system and a severely neglected one ranges from 10 to 25 percent.
Regular Maintenance
- Clean or replace filters regularly (every 2 to 6 months, depending on operating time and amount of dust in the environment).
- Clean and flush the drain line
- Remove plant life and debris from around the outdoor vent.
- Clean evaporator coil and condensate pan every 2 to 4 years.
- Clean the blower's fan blades.
- Clean supply and return registers and straighten their fins.
- Inspect ducts, filters, blower, and indoor coil for dirt and other obstructions.
- Diagnose and seal duct leakage.
- Verify adequate airflow by measurement.
- Verify correct gas pressure by measurement.
- Check for fuel leaks.
- Inspect electric terminals, and if necessary, clean and tighten connections, and apply nonconductive coating.
- Lubricate motors, and inspect belts for tightness and wear.
- Verify correct electric control, making sure that heating is locked out when the thermostat calls for cooling and vice versa. Verify correct thermostat operation.
- Test with an electronic combustion analyzer the performance efficiency of the heating system.
Improving Performance
Poor installation, duct losses, and inadequate maintenance are problems for heating systems. A growing body of evidence suggests that most heating systems have significant installation or service problems that reduce performance and efficiency.
Increasing Airflow in Heating Systems
The capacity and the efficiency of an heating system depends upon adequate airflow. There should be about 400 to 500 cubic feet per minute (cfm) airflow for each ton of the units air-conditioning capacity. Efficiency and performance deteriorate if airflow is much less than 350 cfm per ton.
An ideal duct system has both a supply register and a return register for every room. Most homes, however, have only one or two return registers for the entire house. Air from other rooms must find its way back to these registers to be reheated or re-cooled. Obstructions in return air are a common air circulation problem, particularly from closed interior doors to rooms with no return-air registers.
Blockage of supply or return air ducts and registers can pressurize or depressurize portions of the home, resulting in poor performance and increased air leakage through the building envelope. Restrictions to airflow have the greatest impact on the return-air side of the system, so repairs should start with the return ducts.
Air from every supply register must have an unobstructed pathway back to a return register. You can install louvered grilles through walls or doors, ducts between rooms, and/or additional return ducts and registers to improve air circulation.
Technicians can increase the airflow by cleaning the evaporator coil, increasing fan speed, or enlarging the ducts especially return ducts. Enlarging ducts may seem drastic but in some cases, might be the only remedy for poor comfort and high energy costs.
Air-Sealing Ducts
Measurements of a heating sytems performance indicate that duct leakage wastes 10 to 30 percent of the heating and/or cooling energy in a typical home. It's one of the most severe energy problems commonly found in homes because the leaking air is 20° to 70°F warmer than indoor air in winter and 15° to 30°F cooler in the summer.
Duct leakage may cause some minor comfort problems when ducts are located in conditioned areas. But when leaky ducts are located in an attic or crawl space, the energy loss is often large. Some of the worst duct leakage occurs at joints between the air handler, and the main supply and return air ducts. Some main return ducts use plywood or fiberglass duct-board boxes. These boxes frequently leak because their joints are exposed to the duct system's highest air pressures. Heating and air-conditioning contractors often use wall, floor, and ceiling cavities as return ducts. These building-cavity return ducts are often accidentally connected to an attic, crawl space, or even the outdoors, creating serious air leakage. Fiberglass ducts and flex ducts are often installed improperly. These ducts may also deteriorate with age, leading to significant supply-duct leakage.
The best heating and cooling contractors have equipment to test for duct leakage. Testing helps locate duct leaks and indicates how much duct sealing is necessary. Do not use duct tape for sealing its life span is very short, often less than 6 months.