In a comment under your question, you said that you mostly follow APA style.
This is what the Publication Manual of the American Psychological Association (6th ed.) says:
- en dash: An en dash is longer and thinner than a hyphen yet shorter than an em dash and is used between words of equal weight in a compound adjective (e.g., Chicago–London flight). Type as an en dash or, if the end dash is not available on your keyboard, as a single hyphen. In either case, no space before or after.
Although this doesn't specifically address number ranges (as opposed to words), number ranges are mentioned in the APA Style Blog post "Computer Editing Tip: En Dashes":
The Publication Manual shows en dashes for
- items of equal weight (e.g., test–retest, male–female, the Chicago–London flight),
- page ranges (e.g., in references, “... Journal of Applied Psychology, 86, 718–729.”),
- and other types of ranges (e.g., 16–30 kHz).
This, too, does not explicitly discuss non-integer number ranges. However, in the absence of any other guidance, the prevailing guidance—due to consistency and a lack of any reason not to—remains to use en dashes without spaces.
If you have seen en dashes with spaces surrounding them, then they are there because other styles guides or house styles have been followed.