Ordering entries by custom field (integer)
Craft 2
Either of these should work (they are equivalent):
{% set entries = craft.entries.width('&gt; 0').section('windows').order('width') %}

or
{% set entries = craft.entries({
  section: 'windows',
  order: 'width',
  width: '&gt; 0'
}) %}

The reason you are getting &quot;Array to string conversion&quot; error is that find has turned your ElementCriteriaModel into an array.
Craft 3
order is now orderBy
Craft 3 Docs: Element Queries