I myself don't use non-IRS sources to make such determinations. Take a look at IRS Publication 527, page 12 starting at the bottom of the middle column here , and IRS Pub 334 Chapter 5 page 21, section for "Real Estate Rents" here I've copied what I consider the relevant portions of 527 to your query with the specific part in bold print. This will help you make a more educated determination, and easier to deal with an IRS challenge if it happens.
Providing substantial services.
If you provide substantial services that are primarily for your tenant's convenience, such as regular cleaning, changing linen, or maid service, you report your rental income and expenses on Schedule C. Use Form 1065, U.S. Return of Partnership Income, if your rental activity is a partnership (including a partnership with your spouse unless it is a qualified joint venture). Substantial services don’t include the furnishing of heat and light, cleaning of public areas, trash collection, etc. For more information, see Pub. 334, Tax Guide for Small Business. Also, you may have to pay self-employment tax on your rental income using Schedule SE (Form 1040), Self- Employment Tax. For a discussion of “substantial services,” see Real Estate Rents in chapter 5 of Pub. 334
