CENTRAL DUCTED COMFORT, BUILT TO LAST
Hydronic central air handling units for ducted HVAC systems — residential and large commercial AHUs that heat, cool, humidify, and dehumidify from a single air-to-water heat pump loop.
Central ducted air | Heat & cool | Heat pump ready
An air handling unit (AHU) conditions and distributes air for a whole building or a large zone through a duct network. A blower draws return air across a coil that heats or cools it, then pushes that conditioned air out through the supply ducts to every room. It is the central engine of a ducted HVAC system.
A hydronic AHU like the APOLLO Central AHU uses hot or chilled water at that coil — not refrigerant. An air-to-water heat pump sends hot water in heating mode and chilled water in cooling mode to the same coil, so one outdoor unit drives whole-building comfort through your existing ductwork. The APOLLO Central AHU is built and sized for this air-to-water application.
A hydronic AHU carries its heating and cooling energy in water, which keeps the refrigerant charge outside at the heat pump. There are no refrigerant lines running through the building and no packaged rooftop compressor to maintain. The same water loop that feeds the AHU can also serve fan coil units, radiant floors, or domestic hot water — all from one outdoor unit.
For retrofits, this means the APOLLO Central AHU can replace an outdated forced-air unit while reusing your existing ducts, upgrading airflow, temperature control, and indoor air quality without tearing out the duct system. For new construction, it centralizes heating, cooling, humidity control, and evaporative cooling in a single cabinet tied to the APOLLO Air to Water Heat Pump.
All three APOLLO Central AHUs are hydronic and heat-pump ready. The right model depends on the size of the space and whether the application is residential, light commercial, or large commercial.
Residential and light commercial ducted systems. 1400 CFM airflow, high-efficiency 800W fan, hydronic coil up to 193,600 BTU. Upflow standard; downflow and sideflow special order.
View productLarger residential and light commercial systems. 2400 CFM airflow, coil up to 460,000 BTU, with humidification, dehumidification, backup heating, and evaporative cooling.
View productLarge commercial ducted systems. Full comfort functions with backup heater and automatic-feed evaporative cooling; designed to replace outdated central duct systems.
View productA central system that conditions and distributes air for a whole building or a large section through ductwork. One AHU serves many rooms from a single cabinet. Best when you already have — or want — a central duct system and prefer one unit doing the work.
A compact, room-level device that conditions one zone with no central duct network. Each fan coil is controlled independently. Best for ductless installs, retrofits, and room-by-room zoning. See the hydronic fan coil units collection.
The APOLLO Central AHU brings several climate functions into one central cabinet:
Hot water heats and chilled water cools at the same coil — every model, both seasons, fed by the air-to-water heat pump.
The 6 and 25 Ton models add humidification and dehumidification for steadier, more comfortable whole-building air.
An integrated cooling pad with automatic water feed on the 6 and 25 Ton models provides free or backup cooling.
The 6 and 25 Ton models include a backup heater for demanding loads and large commercial conditions.
The 3.5 and 6 Ton ship upflow as standard, with downflow and sideflow available as special order.
A hydronic AHU has no indoor refrigerant circuit to service, which keeps upkeep straightforward. A few regular checks keep it running efficiently:
Clean or replace the return-air filter on a regular schedule based on use and air quality.
Keep the coil clear and supply and return grilles unobstructed so airflow stays strong.
If using evaporative cooling, check the cooling pad and confirm the automatic water feed is supplying it.
Inspect the condensate drain when cooling, and check duct connections and registers periodically.
Verify thermostat and control settings at the start of each heating and cooling season.
Air Handling Unit FAQ
Direct answers about how hydronic air handling units work, compatibility with air-to-water heat pumps, how an AHU differs from a fan coil or rooftop unit, sizing, installation, and maintenance.
An air handling unit (AHU) is a central HVAC device that conditions and distributes air for a whole building or a large zone through a duct network. Inside, a fan draws air across a coil that heats or cools it, and the unit delivers that conditioned air through supply ducts. A hydronic AHU like the APOLLO Central AHU uses hot or chilled water — supplied by an air-to-water heat pump, boiler, or chiller — as its heating and cooling source rather than refrigerant.
A blower pulls return air through a filter and across a water coil. In heating mode the coil carries hot water; in cooling mode it carries chilled water. The air is conditioned as it passes the coil and is pushed out through the supply ductwork to each room. The APOLLO Central AHU also humidifies, dehumidifies, and can run integrated evaporative cooling, all from one central cabinet tied into your duct system.
A hydronic air handling unit uses water — not refrigerant — to carry heating and cooling energy to its coil. Hot or chilled water is produced by a central source such as an air-to-water heat pump and circulated to the AHU through insulated pipes. This lets one outdoor heat pump feed the AHU, and other emitters like fan coils or radiant floors, through a single water loop, with no refrigerant lines running through the building.
Yes. The APOLLO Central AHU is designed to pair with the APOLLO Air to Water Heat Pump. The heat pump produces hot water for heating and chilled water for cooling, and the AHU uses that water at its coil to condition the air it distributes through your ducts. It connects to the same hydronic loop that can also serve fan coils, radiant floors, or domestic hot water.
An air handling unit is a central system that conditions and distributes air for an entire building or large section through ductwork. A fan coil unit is a compact, room-level device that conditions a single zone with no central duct network. Use an AHU for whole-building ducted comfort; use fan coils for individual room or zone control. Both APOLLO options run on the same hydronic heat pump loop.
A packaged rooftop unit (RTU) is a self-contained refrigerant system that sits outdoors and blows conditioned air down into the ducts. An air handling unit is typically installed indoors and, in a hydronic setup, carries no refrigerant — it conditions air using hot or chilled water from a separate heat pump or boiler. The hydronic AHU keeps the refrigerant charge outside at the heat pump and lets the same water loop serve other parts of the system.
Yes. Because the coil can receive either hot or chilled water, every APOLLO Central AHU heats and cools from the same cabinet. The 6 and 25 Ton models also humidify, dehumidify, and add integrated evaporative cooling and a backup heater for larger and commercial loads.
Sizing depends on the square footage, insulation, climate, and load of the space the AHU serves. The APOLLO Central AHU comes in 3.5 and 6 Ton models for residential and light commercial ducted systems, and a 25 Ton model for large commercial buildings. The right size comes from a load calculation — MBTEK can help confirm the correct model for your project.
Upflow and downflow describe the direction the AHU moves air. An upflow unit pulls air in low and discharges it out the top — common for basement or closet installs with ducts overhead. A downflow unit discharges air out the bottom — used when ducts run below, such as an attic install. The APOLLO Central AHU 3.5 and 6 Ton ship upflow as standard, with downflow and sideflow available as special order.
Yes. The APOLLO Central AHU is designed to replace or upgrade an outdated central duct system. It reuses your existing ductwork while improving airflow, temperature control, and indoor air quality, and it swaps refrigerant-based equipment for a hydronic system driven by the APOLLO Air to Water Heat Pump. This is a common way to modernize an older forced-air system without tearing out the ducts.
Evaporative cooling uses a wetted pad and an automatic water feed to cool incoming air as water evaporates. In the APOLLO Central AHU it provides free cooling in suitable conditions or backup cooling when needed, reducing how hard the rest of the system has to work. The water feed is automatic, so the pad stays supplied without manual filling.
Keep the return-air filter clean or replaced on a regular schedule, keep supply and return grilles clear, and inspect the coil, condensate drain, and ductwork periodically. If you use evaporative cooling, check the cooling pad and the automatic water feed. Confirm thermostat and control settings at the start of each heating and cooling season. A hydronic AHU has no indoor refrigerant circuit to service, which keeps upkeep straightforward.
