Robert Butler - Aspect Inspection

Thermal Bridging Explained - Fine Homebuilding What is thermal bridging? Energy nerd Martin Holladay explains how to improve the effectiveness of insulation.

Drain-Waste-Vent Systems - Fine Homebuilding The pipes that make up a house’s drain-waste-vent (DWV) system are the exit for the water provided through the supply lines. They also carry waste from the toilet, and they connect to outside air for venting sewer gas and relieving pressure.

All air handling systems have this risk.
It's not always visible or even accessible to the non-professional.
Your heat pump, air conditioning, humidifier, dehumidifer, HRV (heat recovery ventilator) and furnace are all air handling systems.
They all need regular cleaning and periodic replacement of filters.
This article describes overhaul cleaning.
Basically the equipment is taken apart, cleaned and reassembled.
If you haven't had it done or can't remember when it was last done, it's time.

'I had no idea,' heat pump owner says about potential for mould As more and more homeowners turn to heat pumps, many seem unaware of the potential for mould buildup and the need for regular deep cleaning.