How much wood needed?

Thanks everyone. I have about 6 already but I'm gonna get another 4. Thinking about adding an Auf, is it worth the $$

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Yes it is. It does not need to be very expensive. A squirrel cage blower that will make a big difference can be had for less than $100 on eBay. If you have an old oil burner kicking around you can use that, just remove the ignition parts.