Why is my circulator pump heating my house?
High probably you have non-insulated pipes or components in the area of the vent system.

If you do not want completely and professionally remounting the hot water pipe, you have various ways to reduce the heating of the air:


Insulate the hot water pipe as much as possible. There are suitable foamed insulations that can be easily pushed over pipes. But you have also to find suitable places in the ventilation duct for inserting.
What is the temperature of the hot water? You can set the temperature of the water to 55°C/131°F. Or lower if the system has automatic intermediate heating to combat of legionella.
Put a electric timer to the circulation pump. If you do not need hot water all day, you can limit the duration of the hot water pipes.