Wiltshire Police have a team of 16 officers looking into the historical allegations against the late prime minister, MPs were told.
The force launched its investigation last August and is “committed to going where the evidence leads”, Chief Constable Mike Veale said.
In a letter to the Home Affairs Select Committee he said: “As with all investigations, the length of the enquiry will usually be commensurate with the complexity, seriousness and volume of allegations.
“I would ask no inference is drawn, suffice to say I am satisfied the length of this investigation is proportionate.”
Detectives are probing several allegations of abuse against Sir Edward, who led the Conservative government between 1970 and 1974, and died aged 89 in July 2005.
Former friends and colleagues of Sir Edward have rallied to defend his reputation and criticised the way the investigation is being handled.
Committee chairman Keith Vaz said: “Concerns have been expressed to the committee over the rationale for this investigation and its cost.
“Ministers have previously criticised the inappropriate decision for a senior police officer to appeal for individuals to come forward with information at the gates of Sir Edward Heath’s former home.
“We will be monitoring this issue closely.”