No. Just like with a mortgage, refinancing requires you to get an appraisal to ensure that the loaned amount lines up with what your house is actually worth. A home value estimator is too unreliable for any lender to take seriously. It's best used for a ballpark home value estimate. Learn more about home value website accuracy rates.
Because an appraisal is done in-person, the appraiser has a better idea of the condition of your home than a home estimator does. That can mean the appraised value of your home — and therefore what you can refinance it for — may be far from what an online home value estimator says.
But a home value estimator can give you a ballpark estimate of how much you may be able to refinance for — just don’t be surprised if that estimate ends up being far from what a bank will actually lend you.