The blaze which extensively damaged Masterton Medical on Tuesday night, disrupting services to thousands of patients, is likely to take months to work through.
Moving back into the building was "a good three months away", said Paul Cocks, general manager, Masterton Medical.
He said insurance assessors were inspecting the building at the moment, which may need complete rewiring and a new air-conditioning system.
"I expect it will cost several hundreds of thousands of dollars," said Mr Cocks.
Since the fire, Masterton Medical has been open to acute patients only at the Hiki Te Ora clinic in the Winz building on Lincoln Rd.