313A Refrigeration and Air Conditioning Systems Mechanic is the full trade: any cooling or heating-cooling system in a residential, industrial, commercial or institutional setting, and it is a Red Seal trade. 313D Residential Air Conditioning Systems Mechanic has the same scope "but is limited to" an independent unit in a residential family dwelling, at no more than 240 volts single phase, a 60 amp branch circuit, 60,000 Btu/h of cooling and a saturated suction above 2 degrees Celsius; it is an Ontario-only trade, not Red Seal. 313D takes 4,500 hours of training, 313A 9,000. If your work is houses and their split systems and heat pumps, 313D covers it; for anything larger, commercial or refrigeration, you need 313A. Both are compulsory trades, and both certificates come from Skilled Trades Ontario (STO).
Try free 313D questionsGet all 550 – $69
01313A and 313D at a glance
| 313D Residential AC | 313A Refrigeration and AC | |
|---|---|---|
| Scope | Residential AC and heat pump systems inside the s. 119 limits | Any cooling or heating-cooling system, residential, industrial, commercial or institutional |
| Red Seal | No, Ontario only | Yes |
| Compulsory in Ontario | Yes | Yes |
| Training hours | 4,500: 4,020 on the job + 480 in school | 9,000: 8,280 on the job + 720 in school |
| In-school levels | 2 | 3 |
| Academic entry | Grade 10 | Grade 10 |
| Certifying exam | STO provincial exam; 70% to pass; no published question count | Red Seal exam; 125 questions, four hours, 70% to pass |
| Certificate | STO Certificate of Qualification | STO Certificate of Qualification, through the Red Seal exam |
Sources: STO's trade pages for both trades, O. Reg. 875/21 and 877/21 on e-Laws, and, for the 313A exam, our 313A exam guide.
02What is the difference in scope?
The difference is set in one regulation, O. Reg. 875/21. Section 116(1) gives 313A a scope that covers "any cooling system or heating-cooling combination system that is installed and used in a residential, industrial, commercial or institutional setting": planning and laying it out, installing and starting it up, refrigerant piping, maintaining, servicing and repairing it, including its electrical and electronic components, and commissioning and decommissioning.
Section 119(1) gives 313D the same scope, "but is limited to" residential air conditioning systems that meet two requirements: the system "must be installed as an independent unit in a residential family dwelling", and it must operate at no more than 240 volts single phase, with a branch circuit of at most 60 amps, a cooling capacity of at most 60,000 Btu/h and a saturated suction temperature above 2 degrees Celsius (35 degrees Fahrenheit) in the cooling cycle. Section 119(2) leaves out portable, factory-precharged plug-in appliances of up to 240 volts.
So a house's split air conditioner, ducted heat pump or ductless system is 313D work. A rooftop unit on a plaza, a three-phase system, a walk-in cooler or freezer, a chiller or an ice rink is 313A work. For neither trade does the C of Q cover work that needs a Technical Standards and Safety Act certificate, such as gas work on a furnace (s. 116(3)); that needs a TSSA gas ticket.
03How long does each apprenticeship take?
STO sets the training for 313D at 4,500 hours, about two and a half years: 4,020 hours on the job and 480 hours in school, in two levels. 313A is twice as long, at 9,000 hours, about five years: 8,280 hours on the job and 720 hours in school, in three levels. Both trades ask for Grade 10 to start, under O. Reg. 877/21.
The two share their start. Level 1 of the in-school curriculum is a common core for 313A and 313D: trade practices, cooling cycle fundamentals, components and accessories, electrical fundamentals, cutting, soldering, brazing and welding, installation and basic maintenance. 313D's Level 2 then turns to the house: psychrometrics, heat load calculations, residential AC systems, air distribution and residential electrical and control systems. Both trades also need an ODP card under O. Reg. 463/10 to service or test refrigeration equipment.
04Is 313D a Red Seal trade?
No. 313D is not a Red Seal trade: it is an Ontario-only certificate, and its exam is a provincial one that STO sets and delivers. STO's own trade page tags 313A as a Red Seal trade, and the 313A exam is the interprovincial Red Seal exam for Refrigeration and Air Conditioning Mechanic.
That matters if you may work outside Ontario. A Red Seal endorsement is recognized across the provinces and territories; a 313D certificate is an Ontario certificate for Ontario's compulsory residential trade.
05How do the two exams differ?
The 313D exam is STO's provincial Certificate of Qualification exam. STO's 313D counselling sheet sets a 70 per cent pass mark and weights six skill sets, from Plan and Prepare at 7 per cent to Assemble and Install, Service and Maintain at 21 per cent each, but the sheet is dated 2016 and follows the older training standard. STO publishes no 313D question count, only that its exams have between 90 and 150 multiple-choice questions and up to four hours. The 313D exam guide covers it in full.
The 313A exam is the Red Seal exam. As our 313A exam guide sets out, it has 125 multiple-choice questions in four hours and a 70 per cent pass mark, spread over six major work activities set by the Red Seal Program, with a formula sheet and an acronym list provided at the sitting. Its scope runs across the whole trade, from residential heat pumps to supermarket racks, ammonia plants and chillers, which is what 313D candidates do not have to study.
In Ontario, both exams are booked through STO.
06How many people hold each certificate?
STO's Fair Registration Practices reports for 2024 and 2025 give these figures:
| Figure | 313D 2024 | 313D 2025 | 313A 2024 | 313A 2025 |
|---|---|---|---|---|
| Certificate holders | 3,495 | 3,637 | 9,192 | 9,274 |
| Approved applicants | 321 | 254 | 495 | 411 |
| New Certificates of Qualification | 297 | 246 | 445 | 377 |
313A has about two and a half times as many holders, but 313D accounts for a large share of new certificates: in 2025, 246 new 313D C of Qs against 377 for 313A. STO publishes no pass rate for either exam.
07Can you go from 313D to 313A?
The trades are built to connect. STO's notice for the 2023 313D training standard says it was updated in parallel with 313A's, and that the alignment "better supports a smoother transition between the full trade (313A) and residential trade (313D)". The Level 1 curriculum is already shared.
What STO does not publish, as far as we could find, is a rule that credits 313D hours or a 313D certificate toward 313A, or a set path for a 313D holder to challenge 313A. If you plan to move up, ask STO how your hours and certificate will be counted before you register.
08Which one do you need?
- 313D if your work is houses: replacing and servicing split air conditioners and heat pumps, ductless systems and their controls, within the 240 volt, 60 amp and 60,000 Btu/h limits. It takes half the training time of 313A.
- 313A if you want commercial, industrial or institutional work, refrigeration, three-phase or larger equipment, or a Red Seal endorsement that travels across Canada.
- Either way, you also need an ODP card to service refrigeration equipment, and a TSSA gas certificate for the gas side of a furnace.
For the steps to the 313D certificate, by apprenticeship or by challenge, read how to get your 313D licence in Ontario. To test yourself, try the 313D practice exam or the 313A practice exam.
09Questions people ask
- What is the difference between 313A and 313D?
- 313A is the full refrigeration and air conditioning trade, for any setting, and a Red Seal trade. 313D has the same scope but is limited by O. Reg. 875/21 s. 119 to independent units in a residential family dwelling, up to 240 volts single phase, a 60 amp branch circuit and 60,000 Btu/h of cooling; it is Ontario-only.
- Is 313D a Red Seal trade?
- No. 313D is an Ontario-only compulsory trade with a provincial Certificate of Qualification exam. 313A is the Red Seal trade.
- How many hours is 313A compared with 313D?
- 313A is 9,000 hours, 8,280 on the job and 720 in school over three levels. 313D is 4,500 hours, 4,020 on the job and 480 in school over two levels.
- Can a 313D work on commercial systems?
- No. The 313D scope is limited to systems installed as an independent unit in a residential family dwelling within the s. 119 limits. Commercial, industrial and institutional systems, and residential systems beyond those limits, need 313A.
- Does 313D count toward 313A?
- The two trades share their Level 1 curriculum, and STO aligned the 2023 313D standard with 313A for a smoother transition. We found no published STO rule that credits 313D hours or the certificate toward 313A, so ask STO before you rely on one.
- Which exam is harder, 313A or 313D?
- STO publishes no pass rates, so there is no official answer. The 313A Red Seal exam covers the whole trade, from heat pumps to commercial refrigeration and chillers, in 125 questions; the 313D exam stays within residential systems.
10Sources
- O. Reg. 875/21, Scopes of Practice (e-Laws): s. 116, the 313A scope, and s. 119, the 313D scope. Accessed November 1, 2026.
- Skilled Trades Ontario: Residential Air Conditioning Systems Mechanic: 4,500 hours (4,020 on the job, 480 in school), two levels, compulsory status. Accessed November 1, 2026.
- Skilled Trades Ontario: Refrigeration and Air Conditioning Systems Mechanic: Red Seal trade; 9,000 hours (8,280 on the job, 720 in school); compulsory status. Accessed November 1, 2026.
- STO: Notice of change, 313D Apprenticeship Training Standard, December 4, 2023 (PDF): the update done in parallel with 313A and the smoother transition between the two trades. Accessed November 1, 2026.
- STO: 313A and 313D Curriculum Standard, Level 1 common core (PDF): the shared Level 1 subjects. Accessed November 1, 2026.
- O. Reg. 877/21, General (e-Laws): Grade 10 academic entry for both trades. Accessed November 1, 2026.
- STO: Fair Registration Practices Report 2025 (PDF): holders, approved applicants and new Certificates of Qualification by trade, 2025; the 2024 figures are from the 2024 report. Accessed November 1, 2026.
- STO: 313D Exam Counselling Sheet (PDF): the 70 per cent pass mark and the six weighted skill sets; body dated December 5, 2016. Accessed November 1, 2026.
Read on Skilled Trades Ontario's pages and documents and on Ontario e-Laws on November 1, 2026. The quotations are from Ontario regulations and a short phrase from STO's notice of change; STO's training standards and curricula are otherwise used only for what they cover. The 313A exam figures are those in our 313A exam guide, from the Red Seal Program. Where STO publishes nothing, such as a 313D to 313A credit rule or pass rates, we say so. If you find something here out of date, tell us.
Related: How to get your 313D licence in Ontario · 313D exam guide · 313A Refrigeration and AC Red Seal exam guide · 313D practice exam · 313A practice exam · All guides
11Practice for this exam
TicketPrep has practice exams for both trades: 313D on all six skill sets of STO's counselling sheet, and 313A on the Red Seal exam's six major work activities, every option explained. Each Exam Pass is $69 one time for 120 days, and All-Access at $119 covers 313D, 313A and every other exam on the site.
Ten free questions per trade, no account: free practice questions. How our questions are written and checked: how our questions are made.