In a 5 gallon batch, you're better off using about 1 oz. of light toast American oak chips. The oak chips have more surface area than cubes, spirals or bigger chunks of wood so you'll get a lot more oak flavor out of them. Brewer's tend to overlook that if they're not familiar with using wood chips. I use them in a strong scotch ale and they impart plenty of whiskey oak flavor in my beers. If you use too much oak, the beer will taste overly oaky and you'll never get rid of the flavor. I did a barleywine with 2 oz of the same chips and one year later, the oak flavor is just now starting to fade. Since it's better to add too few ingredients to a beer than too much, go with a lesser amount and just add more if it isn't to your taste.
Here's my procedure:
Two weeks before bottling, I take one ounce of the chips and put them into a 4 oz. bell jelly jar. I cover the chips with whichever whiskey I feel like pouring over them. As i'm not a whiskey drinker, it's usually whichever whiskey I can buy in a mini bottle. I buy two mini bottles (last time Johnny Walker black) and poured them over the wood chips, then I screwed on the jelly jar lid and shook them up a little. Just let them sit for a week in the alcohol. The strong ABV of the whiskey is usually sufficient to sterilize a small amount of wood chips.
After a week (a week before bottling/kegging the beer), I take the wood chips and put them into a small hops bag with a few sanitized glass marbles in it. Marble, a quartz rock or anything chemically neutral that won't leach into the beer will work fine to sink the bag of wood chips straight to the bottom. I put the chips in the hops bag, add the marbles and toss it into the primary.
This is the important part: At 3 days, I start pulling samples of the beer with a turkey baster and taste test it. In my setup, it usually takes about five days to a week to reach a flavor level that tastes like it juuuuuuuuuuuust barely has too much oak flavor than i'd like. This is when it's time to pull out the bag or bottle/keg the beer. As it typically takes about a month to carbonate up a good strong beer, that's enough time for the oak flavor to fade just a crotch hair. If you time it right, you hit a nice sweet spot of whiskey oak flavor that will be in effect in your finished beer for the next six to eight months.
Just remember to taste test it, and rack it off the oak when it just barely exceeds the flavor level you want.
