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Selecting a Home Heating System

By: David K

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Heating system sizing
Residential heating systems need to be properly sized so the home will be comfortable during the coldest weather. If the unit is oversized, energy costs may increase and the home may experience high temperature swings during mild weather. Oversizing also increases cost paid for equipment, money better spent on purchasing more efficient equipment.

Determining the proper size for heating system requires estimating heat loss through the roof, walls windows, basement, and other home components under severe outside conditions. This is the design heat load for the home. For many combustion appliances, size of the unit selected is from 10 to 30 percent above the design heat load. This Oversizing allows the unit to recover quickly from night setback.

The contractor bidding the new heating system should determine the correct sizing using techniques that evaluate the insulating value of the area of each home component. Using “rule-of-thumb for sizing heating equipment often results in a unit that is grossly over or undersized. If this unit is a replacement, using the same size as the existing unit should be strongly discouraged. The old unit may have not been sized properly and energy-conserving improvements may have been made to the home since its installation, reducing the need for heating.

Selecting the most cost-effective heating system
Selection of the most cost effective heating system will depend on price and availability of differing fuels as well as the cost of initial installation. Higher initial investments are often justified by reduced utility costs over the lifetime of the unit.

Methods for estimating annual operating costs of central units are usually provided by manufacturers. To determine the most cost-effective system, it will be necessary to obtain bids from several contractors. The additional cost for the more efficient system must be compared to the energy savings. If this is a new home, the cost if the heating system will be part of the mortgage. If the annual total cost heating energy plus the mortgage payment for one system is less than for another, then the system is cost effective. If you are considering replacing and existing heating appliance, you must decide of the savings from a more efficient system are enough to justify the additional cost. It is important to remember that heating systems are only replaced about every 20 years, so you will have to live with your decision for some time.

Central Warm-Air Heating Systems
Warm-air heating system includes gas-fueled furnaces, electric furnaces, conventional heat pumps, and ground coupled heat pumps. They have in common the warm-air delivery system. Ducts provide a passage for heated and cooled air to and from the conditioned space. While this article focuses on selecting a type of furnaces, understanding the importance of proper duct design and installation on the efficiency of the installed heating system is fundamental to having an efficient system.

Ducts
Ducts must be well sealed. Studies throughout the country indicate duct leakage significantly reduces the delivered efficiency of heating and cooling systems. Sealing with duct tape is not satisfactory because most duct tapes fail within a month or two. The duct installer must use mastic-type sealant or at a minimum, foil-backed tape at all joints.
Return ducts must also be sealed. Return air ducts are often constructed by encasing a standard building cavity with metal or gypsum board. The space between floor joists is often panned off with sheet metal, or sections of interior partitions are covered with gypsum board. Building cavity returns air ducts must be sealed, just like supply ducts.

It is not uncommon to find up to one-inch gaps between sheet metal and floor joists. A powerful furnace fan creates strong negative pressure in the return ducts, drawing air from unheated sections of the home. Because the defects are covered with wallboard, they must be corrected during construction. New techniques in duct sealing allow mastic to be injected into the ducts where it seeks out and seals most holes. However, it is easier to seal ducts correctly during construction rather than attempt to seal after the home is finished.

In addition to sealing, supply and return ducts running outside the heated space should be insulated to at least R-. If they are located outside =, then they should be insulated to at least R-8.

Gas-fueled warm-air furnaces
One of the most common heating appliances is a natural gas or propane fired warm-air furnace. The same appliance can often be set up to burn either propane or natural gas with a change in the burner orifices.
The seasonal energy efficiency of a gas-fired warm air furnace is reflected by the Annual Fuel Utilization Efficiency (AFUE). The higher the AFUE, the more efficient the heating unit.
Gas furnaces have a minimum AFUE of 78 percent but can have AFUE's into the mid 90 percent range. Furnaces with AFUE's below 85 percent are conventional furnaces and use traditional vent systems. Units with AFUE's in the 90 percent range are condensing furnaces and are vented through plastic (CPVC) pipe, often through the sidewall of the house. Condensing furnaces are often referred to high efficiency units and carry a higher initial cost, but lower operating cost.

When evaluating different manufacturers of warm-air furnaces, compare the warranty on both heat exchanger and remainder of the unit. Ask for and check references. If comparing units with different AFUE's, compare the increased initial cost against reduced annual heating costs. A detailed method for estimating annual energy costs is available from the Gas Appliance Manufacturers Association (GAMA) Consumer Directory of Certified Efficiency Ratings.

Several manufacturers offer multi-stage furnaces. These units have both a high- and low heat delivery rating. If it is mild outside, the unit delivers heat at a lower rate. If it is cold outside or the home is recovering from setback condition, the higher delivery rate is used. The principal advantage is the ability to maintain a more constant inside temperature. Any advantage in efficiency will be reflected in the AFUE.

Conventional or electronic thermostats are used to control fuel-fired warm-air furnaces. For maximum efficiency, use of an electronic thermostat will provide tighter temperature control and allow programmed periods of temperature setback. Setting back temperatures at night and during the day if the house is unoccupied can save up to 20% on heating costs.

Electric furnaces
Electric furnaces provide heat by using a series of electric resistance heating elements and a central fan. The fan is similar to a blower in a fuel-fired warm-air furnace. Electric furnaces were once quite popular but increasing electricity prices have made them potentially too costly to operate. In areas where demand for heat is low or where electricity prices are low, they can still be cost effective.

They use warm-air delivery through ducts so they can accommodate air conditioning. Electric furnaces are usually considered to be 100 % efficient.

To learn more please visit http://www.texascentralair.com

Article Source: http://depositarticles.com/

David Kagan has over 20 years mechanical experience. He is currently the President of Texas Central Air, one of the leading HVAC companies serving greater Houston, Texas.To learn more, please visit company website at www.texascentralair.com.

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