I have heard that the darkroom is not the best place to store negatives because of the proximity to chemical fumes, but my choices are limited. I do not have AC in the house and cannot control the temperature except in the colder months (and not in the darkroom). Where I live (Eastern Ontario, Canada), summer is mid-June to mid-September. It can get very cold by November and ridiculously cold in Jan/Feb (-22F/-30C, or even colder for a few days). Here are my options:

1) The darkroom, which is fairly large for a home darkroom (10' x 15' or about 3m x 4.5m) and it is also well-ventilated but has no heat. It is comfortably cool for most of the year (April to October). In the hot months, the temperature in the darkroom stays relatively cool (probably around 68F/20C) except for a short period in the hottest part of the summer when it can touch on 75F/24C in the darkroom. During that time, it can also be quite humid, but this is normally no more than a week or two when it is very hot and humid outdoors. In the winter, the darkroom temperature slowly drops and can go as low as 50F/10C in January and February. When I work in the darkroom in the coldest part of the winter, I use a small heater to bring the room up to 68F/20C. This can be up to 2-3 days a week.

2) The basement, which will be warmer than the darkroom all year: 68F/20C from about October to April, and then it will follow the house temperature and get quite warm in the summer and often humid.

So which is better: cool most of the time with a short high spike in the summer and a lot of cold in the winter; or moderate most of the time with a longer period of higher temperature and humidity in the summer (including a very hot spike for a few weeks in July and August).

Another possibility is add a heating vent to the darkroom which would allow me to keep the temperature up in the cold months but would have no effect in the hot months. The problem there is dust. My house is old (90 years) and full of dust. The forced-air heating system doesn't help in that regard. Have any of you had similar problems with forced-air/dust and are there filters out there which can truly make a difference?