Hydronic Air Handling Units

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.