Well I rather think the effectiveness if this has been over played.
Two different sized terracotta pots balances over 4 tea lights. I understand the whole convection heating theory but sadly this feels no warmer than tea lights alone.
We quite like having the t lights on the table during the evening anyhow. For our warmth though the most effective thing seems to be our fluffy blankets and warming cups of de-caff. Very nice and snugly indeed