Capital gains for a rental house will be higher than for a principle residence. On a principle residence (assuming you meet all requirements) the 1st 500k for a married couple is excluded (i.e., no tax owed). No such exclusion for a rental. Plus for rentals the IRS will recapture the depreciation taken on taxes over the years. Most will be taxed at 20% but it could be higher if total income (including cap gains) goes over a threshold...something like 400K.
Still not a reason to not do it. As time passes the capital gains will just get larger.