Air conditioning and maintenance
It is very pleasant if there is air conditioning. Each B&B room has one and there are also two in the apartment. One in the living room and one in the smaller bedroom. So there are five air conditioners in total.
You can use this for every season, both summer and winter. They can be selected cold, warm, drying or simply blowing. Every guest who stays uses it and that is nice. By using the air conditioning, it attracts and cools the air and returns it to the room. Naturally attracts dust and this is stopped by a filter. This will accumulate and must also be removed.
The air conditioning itself is a closed system, but it does require maintenance to prevent strange odors from spreading. Keeping this clean is important.
There are plenty of products to clean this with a very handy "bag", so to speak, keep the wall and floor clean of "dirt". Clean filters and module and use a cleaning agent. You can then choose to add a product to make it smell nice (or leave it that way, of course). Not everyone likes it.