Heating with Electricity: Electric Furnaces, Heat Pumps

Heat Pump Sample

By: Yale Wolk, Erinson Home Inspections

Electric Furnaces

In many homes the heating system is electrically powered. One such system is the electric furnace, which functions like a gas or oil furnace but does not use combustion to produce heat. Rather it uses electrical resistance heating coils to provide warmth to the air that blows throughout the house. Because there is no combustion, there are no concerns about carbon monoxide or water vapor in exhaust gasses. There is no exhaust since nothing is burning. The electric furnace is a dependable and long-lived heating system and should perform satisfactorily for many years. However, it is an expensive system to operate. The cost for electrical power far exceeds the cost of gas or oil in most of the country, and for this reason, electric furnaces are rarely installed in new construction.

Heat Pumps

In electrically powered systems, the successor to the electric furnace has been the heat pump. Like an electric furnace, a heat pump does not use combustion to produce warm air. It does not burn any fossil fuel. Rather, it uses principles of thermodynamics to absorb heat from one source (typically, the outside air), transport it inside the house and then release it into the house air. To do this, it uses refrigerant, usually R-22 and often referred to as Freon- DuPont’s brand name. R-22 has the unusual property of being capable of absorbing warm air from a source, transportign it and then releasing it elsewhere. As noted, the typical heat pump draws warmth from the air outside the home, and is referred to as an air source heat pump for this reason. In the heating mode, the heat pump will draw warmth from outside air, transport it via copper tubes and then release it inside the house.

Air Handler Unit. A heat pump consists of two units. First is the inside unit, often called an air handler. There are two compartments. Inside one is a large fan (the blower). Inside the other is a device that looks something like an automobile’s radiator. It consists of a series of coils weaving through a finned metal structure. This is the air exchanger, where R-22 circulates through coils, meets the inside house air, and the warmth collected outside is released into the inside air. The warmed air is then blown throughout the house by the fan, and is channeled through a system called ductwork.

Clean equipment is key to the proper functioning of a heat pump. The first step is to maintain a clean filter. The filter cleans the air before it passes through the air exchanger. Dirty filters lead to clogged air exchangers, and early wear on the system. Change or clean the filter regularly-every 30 days.

The filter is inside the return air ductwork, usually at the bottom of the air handler in the basement. (However, sometimes it is mounted inside a return air grill.) Electronic filters are often mounted on heat pumps and perform extremely well in these installations.

Compressor. The second part of a heat pump is outside, and is commonly referred to as the compressor. (Actually the unit is a combined compressor and condenser.) It houses equipment which processes the R-22 and cycles it to and from the unit inside the house. There is a large fan inside this unit, and proper operation of this fan is vital to the system’s functioning. Keep shrubs and bushes away from the unit and the fan. Allow approximatley 30 inches of free space on all sides to provide proper ventillation. If your clothes dryer vent is nearby, be aware that lint from the dryer vent will be drawn by the fan, and can clog the unit’s operation. So you would be smart to relocate one or the other.

The compressor unit must also be kept level. Vital liquids and gases are flowing inside, and severe tilt can disrupt their flow, causing leaks or a malfunction. It is common to see tilted compressors in relatively new homes. This is caused by settlement around the foundation wall, especially in the backfill area established during the construction of the home. This area tends to settle, and since this is typically where the compressor is located, when settlement occurs, the comopressor tilts. If you have a new home, be aware of this, and at the first sign of tilting, have the unit re-leveled.

The compressor is the unit which must be periodically replaced. The design life of the compressor is approximately 15 to 20 years, but few make it past year 10. The average life is 6 to 10 years. The reason is that many homeowners don’t understand that these units need regular servicing-at least once each year. And they have to have a clean air flow, which means a clean filter. If you change the regularly, and if you have a qualified heating and cooling company service your heat pump annually, you should be able to get the full 10 years or more from your compressor. On the other hand, if the filter isn’t changed regularly, and if the system is not serviced, it may not even last for 6 years! The compressor is typically sealed at the factory when it is manufactured, and few can be repaired in the field. For this reason, when your compressor fails, more than likely the compressor-condenser will have to be replaced.

The Art of Heating With A Heat Pump. A heat pump should not be treated like a furnace. A heat pump works best at maintaining a temperature. That allows the basic therodynamics of the R-22 to operate at high efficiency. If you turn down a heat pump thermostat at night, and then quickly turn it back up in the morning, you overwhelm the heat pump’s capability to respond. It will then call upon the back-up source of heat: electrical resistance heating elements built into the system. Auxiliary electrical heating elements are built into the inside unto to provide back-up heat in very cold weather, and to serve you in case of an emergency. As the outside temperature drops, these elements will turn on periodically to assist the R-22 based process of absorbing outside heat. (You may have a special light on your thermostat that comes on when the electrical elements are activated.) If you rapidly turn the thermostat up, you will trigger these back-up heating elements yourself. You’ll get the extra heat, but at a price. Simply set your thermostat at a desired temperature, and keep it there. Just set it and forget it. Leave the thermostat alone. Your system will operate to maintain that temperature and it will do it automatically at its most efficient mode of operation.

Those same back-up heating elements are a safeguard if your compressor ever gives out in the middle of winter. Should that happen, you will lose all your heating capability. But, don’t panic. Simply move the thermostat setting to emergency heat. That converts the unit into an electric furnace, and you’ll get heat in a hurry. But the heat is expensive, since it’s 100% electric resistance heating.

Defrosting. On a cold winter’s day you may be startled to see your heat pump compressor explode in a cloud of smoke. Don’t be alarmed. Ice has built up and it has automatically defrosted. Temporarily it blows hot air through the comopressor, and what you see is steam, not smoke.

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