for input type="number" how to set default value to 0

For a textbox that accept numbers as shown below, how can the default value be set to 0? <input name="smtpPort" type="number" id="smtpPort" size="30" maxlength="50" class="input-full" tabindex="4" value="{{model.PortNumber}}"> Though the value in DB is null, it still shows 0 in textbox. Any help would be appreciated.