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How to choose a commercial HVAC contractor

Updated 23 October 2026 · SEO Dons Editorial

What are the 12 checks?

This guide is published information. The site does not install, maintain or certify anything, and it does not vet, rank or recommend contractors, so each check below is one for the buyer to apply to whichever contractors are being considered. The sections after the table explain the checks that rest on a rule, a register or a standard.

#CheckEvidence to ask for
1F-gas company certificationA copy of the certificate, with number, activities, charge limit and expiry, confirmed on the issuing body's register
2Trade body membershipMembership shown on the body's own register, not only a logo
3InsuranceAn employers' liability certificate, plus details of the other cover held
4Design responsibilityA named designer, and the design calculations or a summary
5Load-calculation methodThe method, inputs and diversity assumptions, per zone
6Commissioning recordsThe procedure, a sample record sheet, and who gives any commissioning notice
7Maintenance offer based on SFG20A schedule by asset, and what each visit covers
8Refrigerant strategyThe refrigerant, the reason for it, the charge, and the plan if rules change
9ReferencesSimilar buildings, with contact details the buyer can use
10SubcontractingWho will do the work on site, and their certificates
11Warranty termsWritten terms, including any conditions about servicing
12F-gas paperworkHow the refrigerant record and certificate numbers are handed over

F-gas certification (check 1). GOV.UK says a company, including a sole trader, must be certified by an approved body to service stationary equipment containing F gas operated by others, and that working with F gas without the correct certification is against the law. Individuals need their own qualifications too, even when they work for someone else. The guide to checking an F-gas certificate sets out how to verify both.

Insurance (check 3). GOV.UK says employers' liability insurance must be in place as soon as a business becomes an employer, with cover of at least £5 million from an authorised insurer, and that a business can be fined £2,500 every day it is not properly insured. Ask to see the certificate. Public liability and professional indemnity cover are separate matters, so ask what is held and whether the limits suit the value of the project and any design work.

Appointments (checks 4 and 10). HSE says CDM client duties apply in full to commercial clients, and that a commercial client must appoint contractors and designers while making sure they have the skills, knowledge, experience and organisational capability.

Gas-fired plant. Where the project touches gas fittings, HSE says that in workplaces such as shops, restaurants, schools and hospitals the work must be done by a Gas Safe registered engineer qualified for it, and that the employer is responsible for checking. The engineer's ID card shows the type of work they are qualified to do and whether their qualifications are up to date. In places such as factories, HSE requires a competent person instead.

How is trade body membership checked?

Membership is voluntary, so it is a quality signal rather than a legal test. BESA describes itself as the UK trade association for building engineering services, and its website has a facility to find a BESA contractor. BESA says its Competence Assessment Standard audit provides independent assessment of members' technical competence and commercial capability, with new members assessed on joining and at the end of their first year, then every 3 years.

Three cautions apply:

  • Check the register, not the logo. Confirm the exact company name against the body's own member search, and note what the entry covers.
  • Related schemes are different things. BESA's site lists the REFCOM F-gas register, SKILLcard registration and the Competent Person Scheme as BESA Group services. REFCOM is a BESA Group company, so a REFCOM entry is an F-gas check and not evidence of BESA membership.
  • Voluntary tiers are extras. REFCOM Elite and the F-Gas Register's FGAS Premium are both described by their operators as voluntary, so neither replaces the legal certificate.

What should the design, commissioning and refrigerant answers look like?

Design responsibility (check 4). HSE says a design includes drawings, specifications and design calculations, and that specialist contractors count as designers when they get actively involved in design work. A contractor that sizes the plant is taking on that role, so the answer should name who is the designer and show the calculation.

Load-calculation method (check 5). Ask which method and software were used, what occupancy, equipment, glazing and solar assumptions went in, what each zone came out at, and what diversity was applied between zones. The guide to sizing commercial air conditioning explains what the numbers mean, and how to compare commercial HVAC quotes shows where they should appear in a bid.

Commissioning records (check 6). In England, regulation 44 of the Building Regulations 2010 requires the person carrying out certain work to give building control a notice confirming the fixed building services were commissioned in accordance with an approved procedure. CIBSE publishes commissioning codes by system type, including Code R for refrigeration and Code A for air distribution. The answer should say which procedure applies, show what measured records come back, and say who gives the notice.

Refrigerant strategy (check 8). GOV.UK says banned F gases must not be placed on the market in Great Britain, and its list of bans in new equipment was last updated on 27 August 2026, so the rules are still moving. Ask which refrigerant is proposed, why, and what the plan is if the rules tighten. The guide to GB F-gas changes covers the direction of travel.

What about maintenance, references, subcontractors, warranty and paperwork?

Maintenance offer (check 7). SFG20 describes itself as the industry standard for building maintenance, and BESA publishes a member list showing who holds an active SFG20 licence. Ask for the proposed schedule by asset, built from SFG20 or an equivalent, with what each visit covers. The maintenance contract checklist goes through what that contract should say.

References (check 9). Ask for two or three buildings similar in use and size, and for contact details the buyer can use directly. Ask what went wrong on those jobs and how it was handled.

Subcontracting (check 10). REFCOM says subcontractors carrying out the work must hold their own company certificate, and that a contractor cannot apply for one on their behalf. Ask who will be on site, who employs them, and see their certificates.

Warranty terms (check 11). Ask for them in writing: duration, parts and labour, exclusions, and any condition about servicing or records. If servicing is a condition, it belongs in the comparison.

F-gas paperwork (check 12). For equipment holding F gas equivalent to 5 tonnes of carbon dioxide or more, GOV.UK says the operator must keep records for 5 years, including the quantity and type of gas when installed and the certificate number of each company used. Ask how the contractor will produce and hand over the installation record.

How should the checks be used together?

No single check settles the choice. Score each contractor against the table and compare the gaps. A contractor that cannot provide evidence for a check has told the buyer something.

Readers who want to put a project to contractors can send an enquiry through the site's form. The same twelve questions apply to whoever responds.

Sources

Common questions

Does BESA or REFCOM Elite membership mean a contractor is better?

It shows the contractor has met that body's own tests, such as BESA's Competence Assessment Standard audit. It is voluntary and it does not replace project-specific checks on design, commissioning and references. Verify it on the body's register.

What if a contractor belongs to no trade body?

Membership is voluntary, so the legal checks still decide eligibility: F-gas certification, insurance and, for gas work, Gas Safe registration. Ask for equivalent evidence on competence and past work.

Do the CDM Regulations apply to a small air conditioning replacement?

HSE says client duties apply in full to commercial clients, and that a commercial client has contractual control and appoints designers and contractors whatever the project size. Whether a particular job counts as a construction project is a question for HSE's guidance.

Does a sole trader need employers' liability insurance?

GOV.UK says the requirement starts as soon as a business becomes an employer, and lists exemptions such as employing only family members. A sole trader with no employees may therefore not hold it, so ask what cover the business does hold.

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