An annual energy consumption simulation is made for one Latvian mansion with swimming pool hall. Building has two main parts: living part (with bedrooms, living room, kitchen, and washing rooms), and a recreation part with 28m² swimming pool, saunas and sports hall. Simulation results show, that swimming pool room consumes 77 MWh of heating energy per year. When using heat pump gained energy to preheat swimming pool supply air, annual heat energy consumption decreases to 62 MWh, which means about 20% saving. The heat pump system annual average coefficient of performance (COP) according to manufacturer’s data is assumed as 2.5. Paper results can be used by HVAC engineers and architects for ventilation and air conditioning design in other multi-purpose buildings with indoor swimming pools.