Offices, shops, clinics, small hotels, and restaurants sit in an awkward middle ground. They are too large for a residential system specification and too small to justify the engineering approach applied to a hospital or a tower block.
This guide covers what changes when a hydronic system moves from a house into a light commercial building, the decisions that determine whether it performs, and the specification points that are frequently missed at quotation stage.
What Changes from Residential
The technology is largely the same. What differs is how it is used, and that changes the specification in several specific ways.
| Aspect | Residential | Light commercial |
|---|---|---|
| Operating hours | Occupied evenings and weekends | Long weekday hours, often unoccupied nights |
| Occupancy density | Low and stable | High and variable through the day |
| Internal heat gains | Modest | Substantial from people, lighting, equipment |
| Cooling requirement | Often optional | Usually essential |
| Zone count | A handful | Many, often on separate schedules |
| Consequence of failure | Discomfort | Business interruption |
| Electrical supply | Single phase, adequate | Must be verified, may need three phase |
| Documentation | Often absent | Needed for maintenance and compliance |
The one that changes the sizing calculation most. Internal heat gains. A room with twenty people, lighting, and computers generates substantial heat, and in a well-insulated commercial building those gains can meet a meaningful share of the heating requirement during occupied hours. A calculation that ignores them oversizes the system. The same gains are why cooling is usually essential in commercial buildings even in climates where residential cooling is optional.
The Emitter Decision: Fan Coils or Underfloor
This is the decision with the longest consequence, and the answer differs by building type rather than by preference.
Fan coil units
A fan coil takes hot or chilled water from the heat pump and blows air across the coil into the room. Each unit serves one zone with its own control.
Fast response is the main advantage, and in a commercial building it matters. A meeting room occupied for two hours needs to reach temperature quickly, and a fan coil does that in minutes where underfloor heating takes hours.
Cooling is straightforward. The coil handles chilled water directly, and condensate is managed by a drain in the unit. This is the decisive point in most commercial specifications, because commercial buildings need cooling and radiant cooling through a floor requires careful condensation management.
Zone-by-zone control is inherent, since each unit has its own valve and thermostat.
The trade-offs are visible equipment in the space, fan noise, and air movement that circulates dust. Fan coils also need maintenance access and condensate drainage at each unit.
Underfloor heating
Underfloor heating operates at 30 to 45°C flow temperature, which is where a heat pump is most efficient, and it produces even comfort with no visible equipment.
It suits commercial spaces where occupancy is steady through the day and the slow response is not a constraint: retail floors, hotel corridors and lobbies, showrooms, and open-plan offices with consistent hours.
Where it struggles is in spaces with intermittent occupancy and high internal gains, because the thermal mass that produces even comfort also means the floor keeps releasing heat after a room has filled with people and equipment.
Both together
Frequently the right answer rather than a compromise. Underfloor heating in circulation areas, lobbies, and steadily occupied spaces; fan coils in meeting rooms, offices, and anywhere needing fast response or cooling.
Both run from the same heat source and the same water circuit, which is one of the practical advantages of a hydronic approach: the emitter can be chosen per space rather than imposed throughout.
| Space | Usually suits | Why |
|---|---|---|
| Meeting rooms | Fan coil | Intermittent use, fast response, high gains |
| Open-plan office | Either, or both | Steady occupancy but cooling needed |
| Retail floor | Underfloor | Even comfort, no visible equipment |
| Hotel bedrooms | Fan coil | Individual control, cooling, fast response |
| Lobby and circulation | Underfloor | Steady occupancy, comfort underfoot |
| Restaurant dining | Fan coil | High and variable gains, cooling essential |
Sizing and Multiple Units
Light commercial loads frequently exceed what a single residential-scale unit delivers, and there are two approaches.
One larger unit
Simpler to install, fewer connections, one point of maintenance. The 16 kW unit covers a calculated load in roughly the 10 to 16 kW region, which suits a small office, a shop, or a clinic.
Worth knowing: within this range, the largest unit is also the most efficient. The 16 kW achieves a COP of 4.53 at A7/W35 against 4.5, 4.46, and 4.42 for the smaller models, and an EER of 3.14 in cooling against 2.85 for all three. That cooling advantage of roughly 10% matters in a commercial building where cooling runs through the working day.
Several units in parallel
Where the load exceeds what one unit provides, multiple units operating together cover it. This brings three practical advantages in a commercial context.
Better part-load performance. Commercial loads vary widely between occupied and unoccupied hours. Several smaller units allow some to shut down entirely at low demand rather than one large unit cycling.
Redundancy. If one unit fails, the others continue. In a building where heating failure means business interruption, partial capacity is considerably better than none.
Phased installation. Capacity can be added as a building’s use develops rather than committing everything at the outset.
The trade-off is more connections, more controls to coordinate, and more units to maintain.
The figure to check when sizing, as always, is the minimum. The 16 kW unit modulates from 6.5 to 18.0 kW, so it cannot produce less than 6.5 kW. In a building whose demand falls well below that outside occupied hours, it will cycle rather than modulate. Where load varies widely between day and night, several smaller units frequently outperform one large one for exactly this reason.
Electrical Supply: Verify Before Committing
The constraint most often discovered late, and the one that can invalidate an otherwise sound design.
A 16 kW unit draws considerably more current than a residential model: 15.8 A in heating at A7/W35, 19.6 A at A7/W45, and 20.0 A in cooling. Multiple units multiply that.
Power supply can be configured as single or three phase, and the correct option should be confirmed with the technical team at specification stage rather than assumed.
Three checks before committing to a capacity:
Is three-phase supply present on site? Many commercial premises have it; many small ones do not.
What spare capacity exists? An existing supply already close to its limit may not accommodate the addition, and upgrading a supply is expensive and slow.
What does the distribution board allow? Available ways and protection ratings determine what can be connected without alteration.
Discovering a supply limitation during commissioning delays handover and costs far more than the check would have.
Zoning at Commercial Scale
A house has a handful of zones. A commercial building has many, often on different schedules, and managing that is where commercial control differs most from residential.
Multiple manifolds
A larger building typically needs several manifolds, each serving an area, each with its own pump and mixing arrangement.
This has a diagnostic benefit: a fault confined to one area points to that manifold rather than to the plant room, which narrows the search immediately.
Label every loop
Trivial at installation and invaluable afterwards. In a building with thirty circuits, identifying which branch serves which room years later is a genuine obstacle at every service visit if nobody labelled them.
A printed schedule at the manifold, and a marked drawing retained with the building documentation, repays the effort at the first maintenance call.
Schedules per zone
Commercial occupancy is predictable, which makes scheduling more valuable than in a house. A meeting room used two hours a day, an office occupied 8 to 6, and a reception area needing warmth from opening all have different requirements.
Where control runs through a building management system rather than individual thermostats, the demand signal reaches the actuators through the BMS. One diagnostic point worth knowing: if a zone is not heating, confirm the BMS is actually calling for heat before investigating the hydraulics, since the fault may be at the control layer entirely.
Control components
Each zone needs a thermal actuator on its manifold branch or fan coil valve, and a room thermostat or BMS signal driving it.
For fan coil applications in buildings that switch seasonally between heating and cooling, the thermostat needs an automatic changeover terminal to respond to the central switching signal. Not all models have one and it cannot be added later, so this must be identified at specification stage.
Fan Coil Valve Selection
Where fan coils are used, valve configuration affects how the whole circuit behaves.
2-way valves either allow flow through the coil or block it. Simple and economical, but when several zones close simultaneously, flow through the circuit drops sharply. This suits systems with variable-speed pumps that can respond.
3-way valves redirect rather than stop. Closing the coil path simultaneously opens a by-pass, so total circuit flow stays constant and the pump is protected from surge. This suits constant-speed pump systems.
3-way with 4-port built-in by-pass integrates the by-pass into the valve body rather than requiring separate pipework, which simplifies installation where many units are involved.
Sizing by Kvs
Valve sizing is determined by Kvs, the flow coefficient in m³/h at 1 bar pressure drop, and getting it wrong produces poor control that no amount of actuator precision corrects.
For adequate control authority, the pressure drop across the valve at design flow should be 30 to 50% of the total circuit pressure drop. A valve too large for its circuit has little authority: most of its travel produces almost no change in flow, and control becomes effectively on/off.
Legom fan coil valves are available in DN15, DN20, and DN25 with Kvs values from 1.4 to 3.1 depending on configuration, rated to 16 bar on constant Kv models, which matters in multi-storey buildings where static column pressure at lower floors is a design consideration.
Noise and Siting
A consideration that carries more weight commercially than residentially, because the unit is frequently near a boundary shared with neighbouring premises.
Many jurisdictions set limits on noise at property boundaries, particularly at night, and for commercial installations demonstrating compliance is often a formal requirement rather than a courtesy.
The Legom 16 kW unit is rated at ≤56 dB(A), only 4 dB above the smallest model in the range despite delivering more than three times the output, because it uses twin fans so each runs at lower speed than a single fan moving the same volume would need to.
Two practical points. Sound reflects off hard surfaces, so a unit tight against a wall or in a corner is heard as louder than the same unit in open space. And check local requirements before selecting a position, since relocating a unit after installation is considerably more expensive than siting it correctly.
Commissioning and Documentation
The stage most often compressed when a commercial project runs behind schedule, and the one that determines whether the system can be maintained.
Balance the circuits. Loops differ in length across a commercial floor plate, and without deliberate balancing the shortest take a disproportionate share of the flow while distant ones are starved. This is the most common cause of uneven temperature complaints in commercial installations, and it is a commissioning task rather than an equipment problem.
Set flow temperature to the lowest the emitters allow. Every degree lower improves heat pump efficiency, and over long commercial operating hours that difference accumulates substantially.
Record everything. Flow temperatures, balanced flow rates, control settings, zone schedules, and the loop schedule identifying which branch serves which space.
Without that record, detecting drift years later becomes guesswork, since a mixing valve that has crept upward changes performance with no visible symptom. In a commercial building that will be maintained by people who were not present at installation, documentation is what makes the system serviceable.
Maintenance Planning
Commercial buildings justify a maintenance schedule in a way houses often do not, because downtime carries business cost.
Service before the heating season, not during it. Contractors are busiest when systems are running, and availability is worst exactly when a failure matters most.
Verify flow temperature annually against the commissioning record, since mixing valve drift is invisible without measurement.
Check zone control per zone annually, confirming each thermostat or BMS signal operates its corresponding actuator.
Keep the outdoor unit clear. Restricted airflow reduces output and efficiency measurably, and commercial plant areas accumulate debris.
Plan for spares. Actuators and thermostats are consumable over a building’s life, and holding a small stock avoids waiting for delivery when a zone fails.
Healthcare and Specialised Buildings
Worth noting the boundary. Clinics and consulting rooms generally fall within light commercial practice, and the guidance above applies.
Hospitals and healthcare facilities do not. Those involve ventilation requirements, pressure relationships between spaces, infection control considerations, and regulatory obligations that go well beyond hydronic heating specification. Our article on HVAC for hospitals covers that context.
Where scald protection is required in care settings, regulations frequently mandate specific delivery temperatures and documented testing. Our guide to scald protection valves covers those components.
“The two things that catch out light commercial projects are the electrical supply and the commissioning. Nobody checks whether three-phase is actually on site until the unit arrives, and then you have a problem that takes weeks and a supply upgrade to solve. And commissioning is what gets cut when a job runs late, which is exactly backwards: on a commercial building with thirty circuits, an unbalanced system means complaints from day one and nobody can diagnose it later because nothing was written down. Both cost almost nothing at the right moment.”
— Maggie Shen, Director of Legom
The Legom Range for Light Commercial
Heat pumps
| Parameter | 9 kW | 16 kW |
|---|---|---|
| Heating range | 3.5–10.0 kW | 6.5–18.0 kW |
| COP at A7/W35 | 4.46 | 4.53 |
| Cooling capacity | 6.5 kW | 14 kW |
| Cooling EER | 2.85 | 3.14 |
| Hot water | 10 kW, 215 L/h | 18 kW, 387 L/h |
| Water port | G1.0 DN25 | G1.0 DN25 |
| Noise | ≤55 dB(A) | ≤56 dB(A) |
| Expansion vessel | Not included | 5 L included |
| Power supply | Single phase | Single or three phase, confirm |
Both use R32 refrigerant with full DC inverter twin rotary compressors, carry an ERP rating of A+++ at 35°C, operate down to -35°C, and hold CE and RoHS certification. See the 16 kW and 9 kW product pages for full specifications.
Distribution and control
Legom manufactures the complete hydronic chain at the same facility: fan coil valves in 2-way, 3-way, and 4-port configurations, manifolds with flow meters on each branch for balancing, thermal actuators in NC and NO configurations with manual override options, room thermostats including a model with automatic changeover for reversible systems, base stations for zone coordination, floor heating pipe with oxygen barrier protection, and the wider HVAC valve range.
Because components are produced together, compatibility is designed in rather than assumed, which removes a category of problem that becomes expensive at commercial scale where many units are involved.
We supply partners in more than 90 countries, with OEM and ODM services across the range. Contact the technical team with your building type, calculated load, and available electrical supply to discuss specification.
Frequently Asked Questions
What counts as a light commercial building?
Offices, shops, clinics, small hotels, restaurants, and similar premises: larger and more heavily occupied than a house, but without the ventilation, pressure relationship, and regulatory requirements of a hospital or large institutional building. The heating technology is largely the same as residential, but operating hours, occupancy density, internal heat gains, zone count, and the consequence of failure all differ, and those differences change the specification.
Should I use fan coils or underfloor heating in a commercial building?
Frequently both. Fan coils respond within minutes and handle cooling straightforwardly, which suits meeting rooms, hotel bedrooms, restaurants, and any space with intermittent occupancy or high internal gains. Underfloor heating gives even comfort with no visible equipment and operates at the low flow temperatures where a heat pump is most efficient, which suits retail floors, lobbies, and steadily occupied areas. Both run from the same heat source, so the emitter can be chosen per space.
How many heat pump units does a commercial building need?
It depends on the calculated load and how much it varies. One larger unit is simpler to install and maintain. Several smaller units in parallel offer better part-load performance when demand varies widely between occupied and unoccupied hours, provide redundancy so a single failure does not stop heating entirely, and allow phased installation. Where load swings substantially between day and night, multiple units frequently outperform one large one.
Do I need three-phase power for a commercial heat pump?
Possibly, and this must be verified before committing to a capacity. A 16 kW unit draws 15.8 A in heating at standard conditions, 19.6 A at higher flow temperature, and 20.0 A in cooling, and multiple units multiply that. Power supply can be configured as single or three phase depending on the installation. Check whether three phase is present on site, what spare capacity exists, and what the distribution board allows, since discovering a limitation during commissioning delays handover considerably.
The proportion of total circuit pressure drop that occurs across the valve, and it should be 30 to 50% at design flow. A valve sized too large for its circuit has poor authority: most of its travel produces almost no change in flow, so control becomes effectively on/off no matter how precisely the actuator positions it. Size by Kvs against the actual circuit conditions rather than by pipe diameter, and check the manufacturer’s flow curves at your design flow rate.
Why does commissioning matter more in commercial buildings?
Because of scale and continuity. A commercial floor plate has loops of widely differing lengths, and without balancing the shortest take a disproportionate share of flow while distant ones are starved, producing complaints from day one. And the building will be maintained by people who were not present at installation, so without recorded flow temperatures, balanced flow rates, and a loop schedule identifying which branch serves which space, diagnosis years later becomes guesswork.
What noise limits apply to commercial installations?
Many jurisdictions set limits at property boundaries, particularly at night, and for commercial installations demonstrating compliance is frequently a formal requirement rather than a courtesy. Check local rules before selecting a position. Note that sound reflects off hard surfaces, so a unit tight against a wall or in a corner is heard as louder than the same unit in open space, and relocating after installation costs far more than siting correctly at the outset.
Does a commercial system need cooling as well as heating?
Usually yes, and more often than a residential building in the same climate. Internal heat gains from people, lighting, and equipment are substantial in commercial spaces, so a building can require cooling during occupied hours even in conditions where a house would not. Reversible heat pumps provide both from one installation, and the 16 kW unit delivers 14 kW of cooling at an EER of 3.14, the highest cooling efficiency in the range.
Reviewed by Maggie Shen, Director at Legom, on October 5, 2026. This guide to light commercial hydronic systems was reviewed for technical accuracy, including verified capacity and electrical draw figures, fan coil valve sizing criteria, and commissioning requirements at commercial scale.