Short answer: about 2 hours.
A heating outage can last about 1 hour.
The tank replacement algorithm is quite simple and consists of several steps.
There is always some oil left in your tank that can still be used, as well as dirty residues (deposits, condensate and even ordinary rubbish) that accumulate at the bottom of the tank.
In our practice we have had one case where we found a wedding ring among the deposits. How it got there is unknown, but the ring was returned to the homeowner who had dropped it in the tank several years ago.
For professional heating oil tank services please contact Brian Carey on 086 806 8776.
Web: https://oiltankreplacement.ie