Dual Fuel Systems

Dual Fuel Systems

Coils

Accessories

To get started click on any of the blue words in this introduction for a more complete xplanation.DESCO Energy and SEER Solutions for Energy Efficient Results will guide you through the entire process of sizing and selecting the most efficient system for your house or business. We recommend all potential customers review all the information provided in ourGetting Started andSolutions section of the web site. When you're ready anOnline Sizing Form using Manual J is provided to complete with detailed construction and sizing of your home including location and insulation values to determine the exact heating and air conditioning requirements of your building. This valuable information provides the necessary information to accurately select and size the heating and air conditioning system that's right for you.

The vast majority of gas furnaces today require a closed combustion system. Most technicians and homeowners mistakenly believe fresh air intake requirements are an energy efficiency feature. However it is required for protection of the heat exchanger, not energy efficiency. A closed combustion system requires both fresh air intake and discharge through pvc or a chimney to protect the furnace. Furnaces many times are located in laundry rooms or in closed basements. Volatile emissions form fabric softener pads or soaps and chlorine bleaches will quickly destroy a heat exchanger when these product fumes come in contact with the combustion flame. To protect the furnace from these types of volatiles including nail polish remover, spray paints or other normal household cleaning agents maximum heat exchanger life is obtained when the air for combustion is taken from outside. Heat exchanger failures caused by volatiles capable of destroying stainless steel heat exchangers are not covered under any manufacturer's warranty. Further there are some home remedies for treating arthritis and other afflictions using chemicals such as DSM which is a dry cleaning fluid. When this chemical comes into contact with a flame it will permeate the metal of the heat exchanger causing a foul rotten egg like odor every time the flame is ignited. The only means of removing the odor is to replace the heat exchanger because it is embedded into the metal. To be safe always use a closed combustion system to protect your new furnace.

When installing you new furnace with a closed combustion system you will either need to make two separate wall penetrations for intake and exhaust air. Using the concentric vent kit eliminates the need for two hole penetrations allowing only one hole penetration creating a more appealing professional appearance. 

While some homeowners may find the cost of installing a concentric vent kit out of their budget the two holes can be made for a closed combustion system and then dressed up with a less expensive decorative vent termination kit. In either option both the concentric vent kit or wall termination kit are substantially more appealing and create a very professional attractive appearance. Nothing looks worse than plastic tubes with various elbow configurations extruding through exterior walls of your home.

Below are the items required for the heat pump section of the dual fuel system. The first item in a split system application is the outdoor condensing unit. Condensing units are rated in capacity and efficiency. The resulting efficiency and capacity are determined in by the correct matching indoor coil or air handler. The capacity ranges from 1.5, 2, 2.5,3,3.5,4 and 5 tons. Efficiency can range from 10 Seer to 18 Seer for cooling and 7.5 to 9.5 HSPF for heating. 15 Seer and 8.0 HSPF and higher efficiency units use 2 staging and the newer R410A refrigerants. As the efficiency and the capacity increases so does the size of the unit. Important to note the outdoor unit must be at least 18" from any walls and clear of any overhead projections for proper air movement.

A dual fuel system installed in conjunction with a furnace will need an indoor coil for the heat pump. DESCO Energy only stocks cased coils meaning there is an insulated wrapper around the coil. If your specific application is to place the coil inside the existing plenum simply remove the wrapper supplied. Removing the wrapper only takes 5 minutes. The difference in cost between a cased and uncased coil is only 4 dollars so rather than stock two different types of coils we only stock cased coils. Coil selection is based on the manufacturers specifications and not on the size of the outdoor unit. For example a high efficiency three ton outdoor unit may require using a 5 ton indoor coil. Today's higher efficiency equipment requires larger coil surfaces on both the indoor and outdoor units. Another factor affecting coil selection is the size opening of the furnace. coils need to be selected to match this size as closely as possible while still maintaining efficiency within the manufacturer's specifications. And another factor affecting coil selection is where you are located. Higher humidity climates require the smaller coils offered by the manufacturer. The smaller coil will produce colder coil temperatures resulting in better dehumidification. For the above reasons it is best to have a NATE certified technical support team member select the matching coil that is best for your specific requirements.

The next item on the list of pictures shows a light condenser pad. Pads are used in lieu of concrete pads for placement of the outdoor condensing unit. In many instances it may be easier to install a condenser pad with a 5" stone base or no base at all. Where there is a slight grade for the location of the outdoor condensing unit or movement of the soil due to heavy rains or freeze thaw conditions it is highly recommended to use a 4" concrete base with 4" stone base. Remember the outdoor unit needs to be located at least 18" from any exterior wall and free of any overhead obstructions.

Risers are required to be placed under the outdoor unit at the four corners. The purpose of the riser is to elevate the outdoor unit so that condensate can drain freely and clear of the unit. Also risers provide protection against snow accumulation. Risers should be considered essential for moisture removal in defrost cycles in every heat pump application whether or not the previous system had them. Risers come in 3,6 and 12 inch heights. Certain codes require the use of 12" risers for flood protection as well.

The next item is the refrigeration lineset that connects the refrigeration system of the heat pump together from the indoor unit to the outdoor condensing unit. Keeping this length as short as possible is important for maintaining maximum efficiency and performance. The standard linesets come in 30 and 50 foot lengths and in three different sizes. With the small line at 3/8" O.D. copper called the liquid line and the larger line called the suction line with insulation the sizes range from 3/4", 7/8" and 1-1/8" O.D. copper. Longer lengths are available.  The size of the suction line is determined by the capacity of the system as well as the length of tubing lineset involved. 3 ton and over systems use a minimum 7/8" suction tubing for 30 feet or less. For 3 ton and over with 50 ft. lengths of linesets they would use 1-1/8" suction line sizes.

If this is a replacement system and you've chosen not to replace the lineset because it is too difficult to replace a filter drier for removing harmful acids and debris and moisture must be installed. It is highly recommended to always replace the lineset when replacing any air conditioning or heat pump system so you are assured everything is clean and fresh and no residual contaminants will infect the new system. If not a suction and liquid line drier should be installed  of the type for removing acid, moisture and filtering.

For a decorative outside professional appearance a lineset thimble can be used to enhance the penetration required for the lineset. Thimbles are available in round and rectangular design.

The electrical whip and disconnect are the next items for the outdoor unit. For every outdoor unit there needs to be an electrical disconnect within sight and reach of the outdoor unit. This is required by all electrical codes in allinstallations. Most new codes require the use of an electrical disconnect with an electrical 110 volt receptacle attached and ground fault protection or GFI. Standard disconnects come with fused or non fused. It is highly recommended to follow the electrical codes in your area. If a GFI type disconnect is required this can also be handy for any service or another outside source for a plug in connection. At the very least a fused or breaker type weather proof disconnect should be used. The ampacity or size of the disconnect should be no less than that required under the HVAC manufacturer's specifications. Keep the electrical disconnect as close to the outdoor unit as possible. The electrical whip is a plastic sheathed protective tube with electrical copper wiring inside to connect electrical power from the outdoor unit to the electrical disconnect. Electrical whips come in one size and rated at 240 volts at 60 amps at 6 feet in length.

The dual fuel thermostat is the next item required. Thermostats come with many different features and programs today. The newest hi tech thermostats provide a wide array of energy saving features such as every day of the year programming with daylight savings features to monitoring hours of operation with reminders for when to change filters. By slowly raising temperatures at different time periods depending on time required, intelligent energy

 management will raise indoor temperatures according to the recovery time required.  In addition they can also control humidity for humidification while monitoring outside air conditions to prevent condensation of walls and windows. A few can actually control variable speed motors to reduce the air speed for a true dehumidification cycle while others will lower the thermostat cooling setting to provide more dehumidification. Some thermostats are internet ready where they can also be monitored or adjusted over the internet or phone or monitor conditions to send alarms. All this with many more functions or to the simplest electro mechanical thermostats are available. Remember the new two stage gas furnaces with variable speed require hi tech 2 stage thermostatic control to operate efficiently.

Outdoor thermostats are required additions to dual fuel systems to provide a changeover in accordance with the balance point. The balance point is where the heat pump capacity due to lowering of efficiency is no longer sufficient to provide the required amount of heating and the gas furnace takes over.  The balance point can be anywhere from 37 to 23 degrees outside temperature.

Electrical thermostat wire needs to be considered for wiring from the thermostat to the indoor air handler or furnace and then to the outdoor condensing unit. Remember thermostat wiring should never be installed inside conduit or plastic sheathing with power wiring. The new hi tech thermostats can require up to 8 conductors from the thermostat to the air handler or furnace while thermostat wiring from the indoor furnace to the outdoor unit will generally require no more than 3 conductors. When running thermostat wire make certain to always run one or two more leads than required for future changes or a broken wire that may occur.

Vibrations pads and corners are used when the indoor air handler or furnace needs to be mounted to raise the level of the indoor unit or to attenuate noise transmission. Corners are recommended when the air handler or furnace is placed in an upright position on a floor with central return. Vibration pads are primarily used in horizontal mounting positions of the indoor air handler or furnace to attenuate noise transmission. Either corners or vibration isolators are very inexpensive and are worthwhile investments.

For furnace installations in basements or closets in upflow applications, furnace legs make installation easier and provide protection from wet floors or water damage. Furnace legs are inexpensive and make a nice attractive installation.

Humidifiers should be considered an essential part of every dual fuel installation for comfort and energy savings. No other single item provides more benefits for such a small investment. Winter air is dry air in all parts of the country. Dry air causes drying of skin and respiratory systems. Dry air also supports viruses and related other bacterial growth. For this reason the flu and other respiratory ailments increase substantially in winter months. Dry air dries out hardwood floors and other furniture and construction materials. As well dry air increases static electricity causing computer and other electronic problems and is shocking when walking across carpeted floors. A humidifier increase indoor air quality and comfort eliminating or reducing the problems cause by dry air. A humidifier can allow you to lower the room thermostat setting 3 or 4 degrees without any noticeable comfort change. Even if a humidifier increased your health to the point you were fortunate to avoid catching the flu or a bad cold, the cost of the lost time at work for on illness more than pays for the cost of the humidifier. Add tot his the savings enjoyed from reduced energy consumption there really is no good reason not to install a humidifier with your new gas furnace. The humidifiers of today are much better than ever with low maintenance and better performance. For serious humidification consider the electric heated humidifiers and for standard humidification there is the low cost bypass and injection humidifiers. Consider a humidifier an essential part of your heating system.

Condensate traps need to be installed in the drain lines of every air conditioning system. Without the use of a trap the negative air pressure inside an air handler or the positive pressure on the coil of a furnace block the natural flow of

condensate and result in overflowing of water from the coil. But condensate traps accumulate debris and need to be cleaned at least once annually and in more hot and humid climates once per month. Traps should be installed with screw type unions where they can be easily removed and cleaned. Pouring hot water down the condensate line can be somewhat effective in checking the operation of the trap. But heavy accumulation will inevitably result in build up that blocks the trap.  Being able to remove and effectively clean the trap with warm running water is the best solution. Traps and condensate lines should be a minimum of 3/4" PVC tubing. Copper and steel drain lines should be avoided as they will clog up faster and are more difficult to keep clean.

All condensing gas furnaces produce water and need to be drained to a sewer line. When a drain access is not readily available such as in a basement or first floor application the use of a condensate pump may be required. Condensate from gas furnaces is drained into the pump reservoir where a float energizes operation of the pump. The water can then be pumped to a local sewer line. Alarm contacts are also provided to deenergize the air conditioning system in the event of pump failure. 3/8" clear plastic tubing is then piped outside or to a local sewer drain. Never drain or pump water from a gas furnace outside as the acid in the water will destroy all vegetation.

The auxiliary drain pan is required when placing a condensing furnace in the horizontal position. Eventually condensate traps will clog unless someone is extremely diligent on constant maintenance. So the attitude should always be when and not if it clogs what damage will occur? In almost all instances horizontal applications are above in an attic area where a condensate trap is not easily accessed for routine maintenance and easily forgotten until they clog. By having an auxiliary drain pan the condensate then flows safely out of the coil on to the auxiliary drain pan and drains safely past the clogged trap. There are also auxiliary drain pans available for vertical or upflow applications. Clogged traps can also result in damaging expensive hardwood flooring or ceilings and floors beneath.

Another protective highly recommended device is the drain alarm. Drain alarms come in two possible applications. One such trap shown can provide an alarm as well as deenergize the air conditioning system until the trap can be safely cleaned. Another senses the accumulation of water build up in an auxiliary drain pan and provides the same protection with an alarm and deenergize the air conditioning system.

Hi efficiency condensing furnaces have special needs and consideration for air filtering. Because of the construction and operation of the furnaces any dirt entering the furnace will actually melt on to the condensing coil. This dirt can't be removed even with steam pressure. Continued build up will result in efficiency losses and premature failure of the furnace not covered under warranty. To protect your furnace and provide continued efficient operation a high media filter is strongly recommended. For proper indoor air quality the air system needs to be properly filtered either using a high media or electronic air cleaner. The high media filter is the most recommended because of higher reliability and visual evidence of proper operation. Electronic air cleaners continue to be less reliable and more expensive to maintain and purchase. Hi Media filter protection is essential to maintaining clean efficient operation of any HVAC system.

In humid climates where mold and mildew are a constant problem the use of an ultra violet lighting system needs to be considered. Ultra violet lighting systems provide the only certain method of controlling and eliminating build up of damaging and harmful fungus and mold spores on wet air conditioning coils.

Protective devices should also be considered for the longest most reliable system performance. If the air conditioning system you are selecting will be operating under unusual circumstances then a low ambient kit should be considered. Low ambient kits provide system protection and efficient operation when the outside temperature falls below 65 degrees.  This type of application occurs in restaurants, computer cooled areas and offices with high heat loads. It can also occur in residential applications where internal areas only are being cooled and the cooling is operating beyond it's design conditions. A low ambient kit cycles or varies the speed of the outdoor fan to maintain a consistent pressure in the refrigeration system essential for efficient operation and protection of the compressor.

Another protective device the hard start kit is used when there is frequent operation of the air conditioning system and/or when there are low power voltages or brown outs. Lower voltages or situations where the refrigeration pressures do not have sufficient time to properly equalize will cause the compressor motor to stall and trip on it's internal overloads creating extreme stress on the motor. Systems using TXVs should also consider the use of hard start kits where undue time is needed for the system refrigerant pressures to equalize. An example of a stalled condition imposed by people can occur by turning the thermostat setting up and down several times quickly. This will cause the compressor motor to stall and trip on it's overloads. With a hard start kit this problem is eliminated and provides extra energy to the compressor motor to overcome problems of insufficient power or rapid cycling substantially increasing compressor life.

A new protective device is also available to monitor and provide added protection to the Copeland Scroll compressors. A very important module which is only available from certain HVAC manufacturers on their highest efficiency models. At the very least the compressor monitor will reduce unnecessary compressor replacements that result from incompetent technicians and contractors misdiagnosing problems. Remember Copeland reports over 35 % of compressors returned under warranty have absolutely no defects and the other 60% are returned with defects that could have been avoided due to improper installations. How many compressors are condemned with no defects out of warranty? You can help avoid this costly mistake and problem as well as provide better compressor protection with the compressor protection module by Copeland.

For customers using propane gas you will require a propane conversion. For single stage gas furnaces this conversion is a simple change of gas orifices. For two stage furnaces the entire gas valve is changed. DESCO Energy will provide the propane conversion for you when requested. We do however advise all customers considering the use of propane gas to reconsider their energy usage. In most parts of the country excluding California the cost of propane gas is more expensive than electric resistance heating. In fact in many parts propane costs 50 to 100% more than electric heat. Ask your technical associate at DESCO Energy about less costly forms of heating. 

Dual Fuel Systems

The most efficient system available is a dual fuel combination system. Dual fuel is exactly as the name implies using two sources of fuel for heating. In the majority of applications this combination is a heat pump with a gas furnace. Another efficient combination is with a heat pump and a fuel oil furnace. What makes a dual fuel system effective, efficient and cost effective is by capitalizing on the maximum efficiency of both systems at the right time. A heat pump is most efficient for heating between outside temperatures of 60 to 35 degrees. At these ambient temperatures a heat pump is more cost efficient for heating than natural gas or fuel oil. At a typical 3.0 coefficient of performance the heat pump will produce 3 times the heat of electric heat and cost less than 1/2 of an ultra efficient gas furnace. A watt of electricity produces 3.4 btus with electric resistance heat. That same watt produces 10.2 btus with a heat pump in moderate outside temperatures as described above.  As outside temperatures fall below the 35 degree mark the heat pump loses efficiency and capacity. A standard heat pump will then use costly electric back up heat to compensate for the loss of efficiency. But a dual fuel system will use a more economical source of heat such as a natural gas or fuel oil furnace.

Dual fuel systems make sense in all areas except in California where electrical energy costs are 3 to 6 times those of the rest of the country. For California it is better to use a natural gas furnace with air conditioning.

For those homeowners having little knowledge of heat pumps please refer to the Heat Pump sub link under Products for a more thorough explanation. Heat pumps more reliable and efficient today than ever. Heat pumps are being used as far north as Canada and as far south as Florida. The average life expectancies are 12 to 15 years on dual fuel applications. 

Most homeowners with natural gas furnaces have air conditioning systems today. And when replacing existing systems or in new construction homeowners want the most efficient systems especially in do it yourself projects. An ultra efficient two stage gas furnace with 95% efficiency and an air conditioning system of 14 Seer is a step in the right direction. But why not put both feet in the right direction and use a dual fuel system?

Here's how and why dual fuel systems cost less to operate and save energy. In a typical winter in Pennsylvania beginning October 1 and ending April 30 the typical weather data will show there are over 70% of the hours during that time frame where the weather is over 35 degrees. A heat pump costs less than 30% to operate than an ultra efficient gas furnace. So for 70% of the winter the heat pump will produce sufficient heat at 30% of the cost of natural gas or 30% of 70%. Since a heat pump costs less than 1/3 of a natural gas furnace this reduces the average dual fuel homeowner's heating costs by 50%. Take a look at your natural gas costs which have increases an average 50% this year. Take 50% off the cost to heat your home and you quickly see the benefits of a dual fuel system. Assuming the average homeowner in Pennsylvania will spend $1,400 in 2006 to heat their home with natural gas that amounts to $700 saved per year and every year thereafter.

The cost to upgrade to a dual fuel system from a gas furnace only heating system with air conditioning will cost an average $350. That $350 investment is returned in less than one winter of usage. In addition you will save that energy costs year after year and more as energy costs continue to skyrocket.

But is dual fuel only cost effective in the northern parts of the country? No! Going further south into South Carolina the dual fuel system will use the efficiency of the heat pump over 85% of the winter resulting in a 75% reduction in energy costs compared to a high efficiency gas furnace. The average cost to heat a home with natural gas in South Carolina is $900 which amounts to $675 saved in energy costs. Again the payback is less than one heating season or a matter of months.

So if you presently are heating with natural gas there is a lot of incentive to consider using a dual fuel system.

Why aren't dual fuel systems a more  common system? When the concept of dual fuel systems was introduced in the 1980s they had elaborate large complicated control systems called dual fuel control centers. There were numerous relays, thermostats, timers and other wiring that was intimidating to most service technicians and installers. Worse none of the control centers were similar in design or functionality. Control centers were an average 2' x 3' control cabinet loaded with wiring and controls.  With each manufacturer having their own specialty method of controlling and operating dual fuel systems not only were HVAC contractors intimidated but homeowners as well. Anytime a service call was required the homeowner knew there was going to be a healthy bill. And there were a lot of service calls right from the beginning. There was a serious reliability factor with the control systems and the heat pumps at that time because all the technology was new and heat pumps were just in their infancy. So a dual fuel system in the 1980s was very much ahead of the times. Heat pumps in their infancy were only to be installed in moderate winter climates such as South Carolina to Florida. Installing a heat pump in that period in the north with a gas furnace was breakthrough science in the 1980s. An experiment to say the least where most of the experiments failing in the first five years. Most air conditioning systems were only given a 10 year life expectancy at that time.

Today heat pumps are produced with ultimate reliability and efficiency for all types of climates. And dual fuel systems are becoming more common everyday. Those elaborate control centers with their large boxes, masses of wiring, relays and thermostats have been replaced by one simple looking device, the room thermostat. Today's new hi tech thermostats have replaced dual fuel control centers. Until 3 or 4 years ago dual fuel systems continued to use smaller control centers with externally wired thermostats. Today all of this technology and control is performed inside the thermostat. The complexity and operation of the dual fuel system is greatly simplified. Diagnostics are much easier and Installation requires no more expertise than the installation of a gas furnace with air conditioning. There are three additional control wires needed in addition to a conventional installation of a gas furnace air conditioning installation. Dual fuel systems were never thought to be in the realm of a do it yourself project but DESCO Energy provides an easy control system installation with the new hi tech thermostats. An outdoor changeover thermostat is required for all dual fuel systems in addition to the main thermostat.

If you have natural gas and want the most efficient heating and cooling system today, make that choice a dual fuel system. SEER - Solutions for Energy Efficient Results strongly recommends the use of a dual fuel system for all homeowners with natural gas or fuel oil.

For homeowners using propane gas a dual fuel system has the highest payback in dollars saved. Due to continued high propane costs it may be more economical to use a heat pump with electric back up heat as electric heating costs are generally less expensive.