[gmac]

I normally use 1 oz of Northen Brewer boiled for an hour in a 6 gallon boil.  Just wondering what would happen if I used 2 ounces of Northern Brewer and only boiled for 30 minutes.  Would I get similar results? 
Thanks

[tygo]

Nope, you'd have a lot more bitterness and more flavor as well.

[gmac]

So can I assume from your reply that you'd advocate 2 oz x 30 min over 1 oz x 60 min?  I am after a good level of bitterness and flavour is certainly welcome.  I would also be adding an aroma or flavouring hop as well. 

[gmac]

I plugged the two versions into beertools.com and here's what I got.
2 x 30 - 48 IBU
1 x 60 - 43 IBU
Both with East Kent Golding added for the last 10 min. 

I also put in 2 x60 - 80 IBU.  I really want to try that but I'm sure it would be all out of balance and taste terrible.  But I do like strongly bitter beers....

[hopfenundmalz]

It depends on how you are estimating your bitterness.  Your online calcualtor has a default setting, which you might want to play around with, or maybe not.  Find what works and stay consistant.

This may help.
http://www.realbeer.com/hops/FAQ.html#units

[bonjour]

I would still boil for 60 minutes unless you have a specific reason for only boiling for 30 minutes.
Whether to add 1 oz at 60 min or 2 oz at 30 minutes depends on what you want in the finished beer.  Style also plays into this.

Look at my Amarillo Pale Ale for a good late hopped beer with lots of flavor and aroma.

[tygo]

I plugged the two versions into beertools.com and here's what I got.
2 x 30 - 48 IBU
1 x 60 - 43 IBU
Both with East Kent Golding added for the last 10 min.  

I also put in 2 x60 - 80 IBU.  I really want to try that but I'm sure it would be all out of balance and taste terrible.  But I do like strongly bitter beers....

As stated above it depends on how you're calculating (estimating) your bitterness.  When I plug that into Beersmith using the Tinseth scale I get:

2 x 30 = 51 IBU
1 x 60 = 33 IBU
Assuming Northern Brewer hops at 8.5% AA, a beginning boil gravity of 1.036, and OG of 1.050, and a 60 minute boil.  I left out the EKG at 10 minutes.

[gmwren]

Don't forget to account for the age and storage method of your hops. This year's leaf will be negligible, but if you are using pellet, it is probably over a year old as I don't think pellet production has ramped up yet. If you use BeerSmith, be aware if you change the age of one hop, it makes all the hops in the data base the same age.