Inverness Castle, a former sheriff court, is being transformed into a new tourist destination.
It had been hoped the 19th Century property, along with neighbouring buildings, could be warmed using sewer water system.
According to Scottish Water, external, showers and washing machines can raise waste water temperature to an average of 15C and systems can be put in place to harness this energy.
Highland Council has asked councillors to grant planning permission the revised project.
A spokeswoman said: “After the feasibility study was completed on the proposed system it was found that flow rates from the sewer on Church Street were not sufficient to support the proposals.
“The sewer on the riverside did have sufficient flow rates but was proving technically difficult to locate and install the correct equipment and get the flow and return pipes from the sewer to the energy centre.”
She added: “The change in the design of the energy system will still achieve the net carbon targets required.”
