The verdict in three sentences
For an air conditioning installer with 12 engineers and 3,500 maintenance contracts, a custom field service management app costs GBP 15,500 to 33,000 (about EUR 18,000 to 38,000) and is delivered in 3 months. The typical gain is around 1 hour per engineer per day, thanks to central scheduling, tablet-signed job reports and invoicing triggered as soon as the customer signs. Off-the-shelf software is often enough below 8 engineers, but beyond that, refrigerant record keeping, annual contracts and accounting integration justify a tool built around your trade.
The build phases
2026 ballpark figures for a development agency, local or remote:
| Phase | Scope | Budget (excl. VAT) | Timeline |
|---|---|---|---|
| Scheduling and routes | Engineer calendar, dispatch, automatic generation of annual service visits | GBP 4,300 to 8,700 | 3 weeks |
| Offline engineer app | Job sheet, photos, parts used, works without signal in plant rooms or basements | GBP 3,900 to 7,800 | 3 weeks |
| Signed report and F-gas record | Customer signature on tablet, PDF emailed, refrigerant added and recovered logged | GBP 2,100 to 4,300 | 2 weeks |
| Automatic invoicing | Invoice generated on signature, export to Xero, Sage or QuickBooks | GBP 2,600 to 5,600 | 2 weeks |
| Customer notifications | SMS confirmation the day before, engineer tracking link | GBP 1,300 to 3,000 | 1 week |
| Dashboards | Jobs per engineer, lead times, contracts due for renewal | GBP 1,300 to 3,600 | 1 week |
Total: GBP 15,500 to 33,000, then GBP 260 to 490 per month for maintenance and hosting. Regulatory point: UK F-gas rules require records of refrigerant quantities for every leak check and service on covered equipment. Building that record into the job sheet avoids a parallel paper register.
Off-the-shelf software or custom build
The calculation below assumes 15 users (12 engineers and 3 office staff).
| Option | Upfront cost | Recurring cost | 5-year cost |
|---|---|---|---|
| Entry-level field service software | GBP 0 to 1,300 setup | GBP 22 to 39 per user per month | GBP 19,800 to 36,400 |
| Mid-range field service software | GBP 1,700 to 5,200 rollout | GBP 43 to 78 per user per month | GBP 40,400 to 75,400 |
| Specialist HVAC ERP | GBP 13,000 to 34,500 | 18 % maintenance per year | GBP 24,700 to 65,500 |
| Custom app | GBP 15,500 to 33,000 | GBP 3,100 to 5,900 per year | GBP 31,000 to 62,500 |
A custom build is therefore not always cheaper. It is justified when off-the-shelf software forces double entry (F-gas, contracts, accounting) or cannot automatically generate 3,500 annual visits with your own frequency and territory rules.
The real gain for a 12-engineer service team
| Indicator | Before (paper and phone) | After | Annual effect |
|---|---|---|---|
| Time lost per engineer | 1 h per day (depot trips, calls, re-keying) | Near zero | 2,580 hours over 215 days |
| Value of that time at GBP 36 loaded | GBP 92,880 of capacity | ||
| Office re-keying of reports | 1.5 h per day | 0.3 h per day | 258 hours, or GBP 6,966 |
| Time from job to invoice | 12 days | Same day | Cash collected 11 days earlier |
| Missed service visits | 4 % of contracts | Under 0.5 % | 140 visits recovered, GBP 19,600 revenue |
| Lost or illegible reports | 5 % | 0 % | Fewer customer disputes |
These are 2026 ballpark figures for a service team still using paper job sheets. Freed time only has value if it is reassigned to billable work.
Mini case study
Fiona, service manager at an air conditioning installer in Glasgow (12 engineers, 3,500 maintenance contracts), wants a cautious estimate. She counts only half of the hour saved, converted into extra 1.5-hour jobs with GBP 80 margin each.
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- Custom app: GBP 25,000
- Maintenance and hosting: GBP 4,100 per year
- Time reassigned: 0.5 h x 12 x 215 = 1,290 hours, or 860 jobs and GBP 68,800 margin
- Recovered service visits: GBP 19,600
Net gain in year one: GBP 59,300. The app pays for itself in about 3.5 months of use.
FAQ
Does the app work without signal?
Yes, the engineer app saves everything offline and syncs when the signal returns. That is essential in plant rooms, and this phase costs GBP 3,900 to 7,800.
Can it handle F-gas record keeping?
The refrigerant record is completed on the tablet, with quantities added and recovered, then archived automatically. Allow GBP 2,100 to 4,300 including customer signature.
Does it connect to our accounting software?
Invoices are pushed to Xero, Sage or QuickBooks as soon as the job is signed. The connector is part of the invoicing phase.
How long to equip the engineers?
Development takes 3 months, followed by a 2-week pilot with 3 engineers. A rugged tablet costs GBP 300 to 600.
What happens to our 3,500 existing contracts?
They are imported from your spreadsheet or current software at go-live, with duplicate checks. The import is included in the scheduling phase.
Let's scope your project. Tell us your number of engineers, contracts and your accounting software, and we will price the app phase by phase with an indicative budget and a 3-month plan. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
