Not every isolation transformer belongs in a clean, climate-controlled electrical room. Outdoor equipment, corrosive facilities, dusty plants, washdown areas,...
Transformer Solutions
for HVAC Systems
HVAC systems are among the largest electrical loads in any building — and among the most demanding on transformers. From rooftop units and chillers to air handling units, pumps, and building automation, Transformer Source supplies dry-type transformers built to handle the motor inrush, VFD harmonics, and continuous duty that HVAC applications demand.
- CSA & UL Certified
- Ships from Canadian Stock
- 3 kVA – 1,000 kVA Range
- Custom Configurations Available
Powering HVAC Systems
Modern HVAC systems are almost entirely VFD-driven — variable frequency drives on chillers, air handling units, cooling towers, and pumps are now standard practice for energy efficiency. This creates significant harmonic distortion on the electrical distribution system, and transformers that aren’t rated for it will overheat and fail prematurely.
Beyond harmonics, HVAC equipment involves frequent motor starts with high inrush currents, outdoor and rooftop installations requiring weatherproof enclosures, and control circuits for building automation systems (BAS) that demand clean, isolated power.
Key HVAC Power Challenges We Solve:
- VFD harmonic distortion: K-factor rated transformers prevent overheating from non-linear VFD loads on chillers, AHUs, and pumps
- Motor starting: Reduced-voltage autotransformers limit inrush current from large chiller and pump motors
- Outdoor & rooftop installations: NEMA 3R enclosed and weatherproof units for RTUs, chillers, and rooftop mechanical equipment
- Control power isolation: Clean isolated 120V or 24V for BAS controllers, thermostats, damper actuators, and VAV boxes
- Voltage conversion: Adapting imported HVAC equipment rated at 208V, 380V, or 460V to Canadian 600V supply
- Mechanical room distribution: Step-down transformers feeding motor control centres and VFD panels in central plant rooms
HVAC Applications We Serve:
- Centrifugal & Screw Chillers
- Rooftop Units (RTUs) & Packaged Systems
- Air Handling Units (AHUs) & Fan Coil Units
- Cooling Towers & Condenser Water Pumps
- Chilled Water & Heating Hot Water Pumps
- Variable Air Volume (VAV) Systems
- Building Automation Systems (BAS)
- District Energy & Central Plant Rooms
- Heat Pumps & VRF Systems
Recommended Transformers for HVAC
The following transformer types are most commonly specified for HVAC mechanical and electrical design. Filter by kVA, voltage, or enclosure using the product search.
Isolation Transformers
3kVA to 750kVA Capacity
Encapsulated Isolation Transformers
0.25kVA to 150kVA Capacity
Autotransformers
3kVA to 1000kVA Capacity
Encapsulated Autotransformers
3kVA to 300kVA Capacity
Control Transformers
25VA to 5000VA Capacity
Motor Starters
10HP to 500HP Capacity
Mini Power Centers
5kVA to 45kVA Capacity
Recommended Transformer Specifications for HVAC Applications
Use the following as a baseline specification guide. Confirm final sizing with your mechanical and electrical engineer of record.
Small Rooftop Unit (< 20 tons) | 5 – 30 kVA |
Medium RTU / Packaged System (20–60 tons) | 30 – 75 kVA |
Large Rooftop / AHU (60–150 tons) | 75 – 200 kVA |
Centrifugal Chiller (100–300 tons) | 100 – 300 kVA |
Large Chiller (300–1,000 tons) | 300 – 750 kVA |
Cooling Tower Fan & Pump Package | 30 – 150 kVA |
Chilled/HHW Pump Group | 30 – 200 kVA |
BAS / Control Panel Power | 0.5 – 5 kVA |
Central Plant MCC Feed | 150 – 750 kVA |
District Energy Plant | 300 – 1,000 kVA+ |
Size at 125% of running load. For across-the-line motor starting without a motor starter, additional sizing headroom is required.
Primary (Input) | 600V or 575V, 3-phase (standard Canadian building supply) |
Secondary — VFD / MCC Panels | 480V or 208V, 3-phase |
Secondary — Control Circuits | 120V or 24V single-phase |
Imported HVAC Equipment | 600V → 208V, 380V, 415V, or 460V as required |
Taps | ±2.5% and ±5% standard — allows fine-tuning for long cable runs to rooftop equipment |
Frequency | 60 Hz standard; 50/60 Hz dual-rated available for imported equipment |
NEMA 1 | Indoor mechanical rooms and central plant electrical rooms — clean, dry environments |
NEMA 2 (Drip-proof) | Mechanical penthouses and above-ceiling locations with potential drip |
NEMA 3R (Rainproof) | Rooftop installations, outdoor mechanical yards, and pad-mount beside condensing units |
Encapsulated | Cooling towers, outdoor condensing units, exposed rooftop locations with high humidity or wash-down |
NEMA 12 (Dust-tight) | Mechanical rooms in industrial or mixed-use facilities with dust or contaminants |
Indoor (Mechanical Room) | Central plant, basement boiler/chiller room, dedicated electrical room serving MCC |
Indoor (Penthouse) | NEMA 2 or NEMA 3R; verify drip and condensation conditions |
Rooftop | NEMA 3R minimum; weatherproof canopy or housekeeping pad; verify wind and snow load |
Outdoor Ground Level | NEMA 3R on housekeeping pad beside condensing units or cooling towers |
Clearances | 18″ sides/top, 36″ front minimum — verify with local AHJ and equipment manufacturer |
Ventilation | Transformer heat output ~2% of kVA rating — factor into mechanical room HVAC design |
Canadian Standard | CSA C22.2 No. 47 — mandatory for all Canadian installations |
US Standard | UL 506 / UL 1561 — for US projects |
Energy Efficiency | NRCan DOE 2016 compliant units available — supports LEED and utility rebate programs |
Electrical Code | CEC Part I (Canada) / NEC NFPA 70 (US) governs installation |
ASHRAE 90.1 | Transformer efficiency requirements referenced in ASHRAE 90.1 energy standard for buildings |
Seismic | Required in BC and Alberta foothills — specify seismic rated hardware for rooftop and mechanical room units |
K-1 (Standard) | Resistive heating loads, simple motor loads without VFDs |
K-4 | Mixed loads with small VFDs or some electronic ballasts — light commercial HVAC |
K-13 Recommended | Any system with VFD-driven chillers, AHUs, pumps, or cooling tower fans — the standard for modern HVAC |
Harmonic Sources | VFDs on all rotating equipment, BAS power supplies, VFD bypass circuits, UPS feeds |
Neutral Sizing | Specify double-sized neutral conductor with K-13 units — standard practice with VFD-heavy HVAC loads |
Consequence of Under-Rating | Standard transformers feeding VFD loads will overheat, reduce service life, and may fail during peak cooling season |
Rule: If more than 20% of the connected load is VFD-driven, specify K-13 minimum. For modern VFD-heavy mechanical rooms, K-13 should be the default specification.
Ambient Temperature | 40°C standard rating; rooftop locations in summer may approach or exceed this — verify and derate if needed |
Altitude | Derate above 1,000m — relevant for Calgary, Edmonton, and interior BC mechanical projects |
Moisture & Condensation | Rooftop and cooling tower locations — specify encapsulated or NEMA 3R with internal heater option |
Vibration | Specify vibration isolation pads for all mechanical room transformers — chiller and pump vibration transmits through structure |
Cold Weather Startup | Canadian outdoor installations — consider low-temperature rated units or enclosure heaters for winter startup |
Seismic Bracing | Required in BC and seismic zones — specify seismic rated mounting hardware at time of order |
Frequently Asked Questions — HVAC
Do I need a K-factor rated transformer for a VFD-driven chiller?
Yes — a K-13 rated transformer is the correct specification for any transformer feeding a VFD-driven chiller or a motor control centre with multiple VFDs. Modern centrifugal and screw chillers are almost universally VFD-driven for part-load efficiency, and their input rectifiers generate significant harmonic currents (5th, 7th, 11th, 13th harmonics). A standard K-1 transformer will overheat under these conditions, reducing service life and risking failure during peak cooling demand. Specifying K-13 is low-cost insurance against a very expensive problem.
What transformer do I need for a rooftop unit installation?
For rooftop units, the transformer must match both the electrical load and the outdoor environment. A NEMA 3R enclosed unit is the minimum for rooftop exposure — it provides rain and weather protection. Size the transformer based on the RTU’s full-load amp rating plus 25% headroom. For modern RTUs with VFD compressors and fans, specify K-4 or K-13 rated. If the RTU is imported and rated at 208V, 460V, or 380V, an autotransformer or isolation transformer with the appropriate secondary voltage will be required. Transformer Source stocks NEMA 3R units in common RTU kVA ranges ready for immediate shipment.
What size transformer do I need for a 200-ton centrifugal chiller?
A 200-ton centrifugal chiller draws approximately 200–250 kW at full load (depending on efficiency rating and operating conditions), which translates to roughly 250–320 kVA at 600V, 3-phase. For a standalone transformer feeding the chiller VFD panel, a 300 kVA K-13 rated isolation transformer is a common specification. If the transformer also feeds chilled water pumps, condenser water pumps, and cooling tower fans, size up to 500 kVA minimum. Always confirm with the chiller manufacturer’s electrical data and the mechanical engineer’s equipment schedule.
Can I use a standard transformer for HVAC motor control centres?
Not recommended if the MCC contains VFDs, which is the case for virtually all modern HVAC MCCs. A standard K-1 transformer feeding a VFD-loaded MCC will experience additional heating from harmonic currents that it is not designed to dissipate. The result is reduced insulation life and premature failure — often timed to peak load periods like summer cooling season. Specify K-13 rated isolation transformers for all MCCs with VFD-driven loads. The cost premium over a standard transformer is minimal compared to the cost of an unplanned transformer replacement during peak building operation.
What transformer do I need for a building automation system (BAS) panel?
BAS panels require small, dedicated control transformers providing clean isolated 120V or 24V power independent of the main building distribution. This isolation prevents ground loops, voltage fluctuations from motor starts, and electrical noise from interfering with BAS controllers, sensors, and communication networks. A control transformer in the 100–500 VA range is typical for a single BAS panel. For a central BAS head-end room with multiple panels and a server, a 1–5 kVA isolation transformer is more appropriate. Transformer Source control transformers are machine-tool rated with high short-circuit withstand — well-suited for BAS applications.
How do I connect an imported HVAC unit rated at 460V to a Canadian 600V supply?
This is a common situation with US-manufactured HVAC equipment (rated 460V/60Hz) installed in Canada where the supply voltage is 600V or 575V. The solution is a step-down autotransformer with a 600V primary and 460V secondary, sized at 125% of the unit’s nameplate kVA. For equipment with onboard control transformers or sensitive electronics, an isolation transformer is preferred to prevent ground fault issues. Transformer Source offers standard autotransformers in all common HVAC kVA ratings for this application — contact us with the equipment nameplate data for a direct recommendation.
Do you stock transformers for fast delivery on HVAC projects?
Yes — we maintain stock of the most common HVAC transformer sizes, including isolation transformers from 15 to 300 kVA in standard commercial voltages, motor starting autotransformers in common HP ratings, and control transformers for BAS applications. Standard stocked units ship within 1–3 business days from our Canadian warehouse. For K-13 rated units, large kVA sizes, NEMA 3R enclosures, or non-standard voltages, lead times are 4–12 weeks. Contact us early in the project schedule — mechanical and electrical contractors frequently need transformer deliveries to align with equipment installation milestones.
What is the difference between using a motor starting autotransformer vs. a VFD for large HVAC motors?
A motor starting autotransformer is a passive, one-time inrush limiter — it reduces voltage during startup, limiting inrush current to 50–65% of across-the-line starting, then the motor runs at full voltage. It is a proven, low-cost solution for motors that don’t require speed control. A VFD (variable frequency drive) provides full speed control throughout operation and is preferred for chillers, pumps, and fans where part-load efficiency is critical. However, VFDs generate significant harmonic distortion — which is why K-13 rated transformers are required to feed them. In modern HVAC design, VFDs have largely replaced reduced-voltage starters for most applications, but motor starting autotransformers remain common for cooling tower fans and pumps in simpler systems.
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Ready to Specify Your HVAC Transformer?
Our technical team works with mechanical engineers, electrical engineers, and HVAC contractors across Canada. Whether it’s a chiller plant, a rooftop unit, or a full central plant MCC — we’ll help you get the right transformer specified and on site when you need it.
Have this information ready:
- HVAC equipment type and nameplate kVA / amperage
- Primary voltage available (600V, 575V, 480V)
- Required secondary voltage
- Number and size of VFDs on the circuit
- Installation location (indoor mechanical room, rooftop, outdoor pad)
- Any special requirements: K-factor, NEMA 3R, NRCan efficiency, seismic