Lone Star Cooling and Heating
Get help with Dual-Fuel Systems
Call Lone Star Cooling and Heating, have us call you, or describe the issue.
Prefer to talk?
Call (325) 219-0005A heat pump paired with a gas or propane furnace, set up so the heat pump handles milder weather and the furnace takes over in the cold, with the switchover point tuned to the building, the climate and local fuel costs.
01Dual fuel
Most dual-fuel trouble is about which heat source runs, and when.
If the furnace fires in weather the heat pump should handle easily, the switchover point may be set too high, or the outdoor temperature sensor may be misreading. Adjusting the controls can shift more of the heating back to the heat pump.
When the heat pump keeps running on the coldest days and the rooms drift below the setting, the handoff to the furnace is not happening. A sensor fault, a thermostat set up for the wrong equipment or a furnace that will not start are the usual causes.
A dual-fuel system is usually set up to favor whichever source is cheaper to heat with at each outdoor temperature. When fuel prices move, or the switchover was never tuned for the building, it can lean on the more expensive one for much of the winter.
Both halves share a thermostat, a blower and often a control board. When neither the heat pump nor the furnace starts, the fault usually sits in one of those shared parts rather than in either piece of equipment.
02Who it suits
Both use a heat pump for most of the year. The difference is what carries the building through the cold.
Winters are cold enough that a heat pump alone would lean hard on its backup, gas or propane is already on site, and the furnace is sound or due for replacement anyway. The furnace carries the coldest weeks with strong, hot air while the heat pump keeps the rest of the season efficient.
Winters are mild, or a model built for cold climates can carry the building by itself. There is no gas line, or the plan is to move away from burning fuel on site. Electric backup in the indoor unit covers the occasional cold snap, and there is no furnace or flue to look after.
Dual-Fuel Systems
Serving Abilene, TX.
03How it switches
The switchover is a decision made by the controls, based on the temperature outside.
An outdoor temperature sensor, or a thermostat that knows the outdoor temperature, tells the controls how cold it is. Above a set point the heat pump heats the building. Below it, the heat pump is locked out and the furnace takes over, and the controls hand back to the heat pump once the weather warms again. In summer the heat pump does all of the cooling.
Where that set point sits is the heart of the system. It can be placed where the heat pump stops keeping up with the building, known as the balance point, or higher, where the furnace becomes cheaper to run than the heat pump. Either way it is a setting rather than a fixed part of the equipment, and it can be moved as fuel prices or the building change.
04The switchover point
The right switchover temperature is different for every building. These are what move it.
Each heat pump holds its output down to a different outdoor temperature. A model built for cold climates can run much deeper into winter before the furnace needs to take over.
A well-insulated, tight building needs less heat on a cold day, so the heat pump keeps up longer. A drafty one reaches the point where it falls behind at a milder temperature.
The cheaper electricity is compared with gas or propane, the lower the switchover can sensibly go. When those prices shift, moving the set point keeps the system running on the less expensive source.
Furnace air comes out noticeably warmer than heat pump air. Some people prefer an earlier handover for that feel, accepting that the furnace then does more of the season.
05Questions
It tends to suit places with cold winters where the building already has gas or propane, or a furnace with plenty of life left in it. The heat pump handles much of the season and the furnace covers the cold stretches. Where winters are mild, a heat pump with electric backup is often the simpler choice.
Normally not. The heat pump indoor coil sits in the furnace airflow, and hot furnace air passing over it while the heat pump runs would push its pressures too high, so the controls run one or the other. Some systems do fire the furnace briefly to warm the air while the heat pump defrosts.
Often it can, in place of the outdoor air conditioner, as long as the furnace is in good condition and its blower and controls can work with a heat pump. The thermostat usually has to be one that manages both, and the indoor coil has to be matched to the new outdoor unit.
What the system is doing, when it started, what the thermostat is set to and what it reads, and whether the outdoor unit is running. The age of the equipment and a photo of its label help a technician arrive prepared.
Lone Star Cooling and Heating
Call Lone Star Cooling and Heating, have us call you, or describe the issue.
Prefer to talk?
Call (325) 219-0005