Today’s high efficiency furnaces include energy saving features which work great but confuse some consumers.
Traditional 80% efficient gas furnaces are very simple – they kick ON when temperature falls a degree or two below set point and then turn OFF when temperature rises a degree or so over set point. The furnace operates at one speed and is either ON or OFF. Room temperature follows a sine wave fluctuation around set point.
Modern furnaces utilize variable speed technology and more sophisticated controls which operate very differently. An informed consumer will want to know:
- Run times are much longer. It may be counter intuitive but operating a furnace at low speeds for long periods of time is more efficient than shorter on / off bursts. No need to worry if a furnace seems to “always be running” during cold weather snaps.
- Discharge air may seem “cooler” than with traditional furnaces. Once again, variable capacity furnaces throttle back heat output to steadily maintain set point.
- Energy code dictates furnace capacity. Bigger is not better. Energy codes have evolved and Seattle heating design parameters call for indoor temperature capability of 72 ˚F at an assumed minimum outdoor temperature of 24 ˚F. In the event of sustained outdoor temperature below design, properly sized systems (as per code) may have difficulty maintaining design indoor temperatures. Most years outdoor temperatures are not extreme and comfort is not an issue. In some instances outdoor temperatures below design are experienced and systems strain to keep up. A slightly upsized system will provide better comfort at extreme conditions but has somewhat higher initial purchase and operating cost.
- Modern furnaces are designed to EFFICIENTLY maintain temperature – not necessarily QUICKLY heat up a cold house – especially under very cold conditions. Gradually “ramping up” heat is more efficient than immediate full capacity operation.
- Variable speed furnaces maintain temperature very close to set point. Sine wave fluctuation of temperature is nearly eliminated – providing increased comfort. Some consumers accustomed to the “overheating” aspect of single speed furnaces may want to increase set point a degree or two to maintain desired comfort. Keep in mind all furnaces operate to maintain temperature at thermostat location. Temperatures may vary somewhat throughout the home depending on heat loss by room and duct work configuration / capacity.
- High efficiency furnaces discharge water (condensate). It is important to keep condensate line free of obstructions and protected from freezing. Do not reposition condensate lines to avoid loss of slope. A “leak” due to failed condensate pump, blocked line, etc is usually easily repaired by a professional.
- Wi-Fi capability is increasingly popular. Manufacturers offer slick Apps which allow consumers to monitor and control heating systems from any smart device. Professional installation is recommended to ensure compatibility and correct wiring. Generic thermostats sold at retail locations are typically lower quality, functionality and cost than manufacturer models designed to be compatible with their specific system.