By default Joomla! Search results are shown on the Home Page template. It is possible to change this by adding a hidden field to the search module.

Within your homepage template folder create a new directory called “html” and then “mod_search”.

Copy the “default.php” file from /modules/mod_search/tmpl/ into your newly created “mod_search” folder under your template folder.

Open this file at near the bottom just before the end of the form add:

<input type="hidden" name="Itemid" value="5" /> 

Save and upload to your site. You should now see your site-wide template loading. Change the value of the Itemid as needed.