Work on fixed water and heating installations needs an autoriseret VVS-installatør (authorised plumbing contractor), or a firm that brings one. Ask which it is, and ask for that on the invoice (faktura). Authorisations are looked up at Sikkerhedsstyrelsen, sik.dk.
Herning is mostly houses and business premises. Distances inside the municipality are longer than in a dense city, so the drive is often a clear line on the quote. The same 4 businesses as the Danish page: Bech´s VVS ApS, GUNNAR KRISTENSEN VVS A/S, Ikast VVS Service A/S, VVS-Installatør Carsten B. Hansen ApS.