I am using SP2013 foundation. Can I configure the refiners on the default search page? When I go to the default search page I cannot edit page.
Follow this blog from Bella Engen, How to add refiners to your search results page in SharePoint 2013
Go to the search settings page of your site and set the "Which search results page should queries be sent to?" as the search centre results page.
If you do not want to/can't set up a custom search page in search centre, then create a webpart page in you site pages. Add the Search Box, Search Results and the Refinement Webparts to the page. Once you have the custom search page, go to the search settings page and set the property "Which search results page should queries be sent to?" as the custom search results page.
You should be able to customize the refiners for the Refinement Webpart as per you need.