1 1/2 inch drain sufficient for a shower?

I have another question about my shower remodel project...

I am replacing a tub and shower combination with a shower only. This is in a condo that was built in the early seventies so the existing drain from the tub/shower is 1.5 inches. Can I reduce a 2 inch show drain down to 1.5 inch and still have sufficient drainage for the shower?

My shower head has a flow rate of 2.5 GPM.

Any thoughts or comments are appreciated.

Thanks!

Our (MN) code is 2". This is due to the fact that the shower does not the storage capacity that a tub has. The shower needs to drain the water quick.

Code in the USA requires 2" for the reasons given. This could entail some significant repiping since nowhere in the line should it go from bigger to smaller. Talk to your local inspector, but they probably won't give you a waiver.

Code in Toronto Canada, and I believe in some areas of the US (Dallas TX for example) does allow for 1.5" since the shower fixtures are limited to 2.5 GPM like tub faucets are.

http://www.dallascityhall.com/pdf/Building/ShowerDrainReduction.pdf

I have a 1.5" drain on my shower and it drains plenty quick enough. I never have any water in the shower pan. It is a Kohler shower unit with a 2" drain, which is reduced on the vertical before entering a 1 1/2" trap.

I think you want what they call a 'bell reducer' as it has a sloped transition vs. creating a flat shelf where it reduces to 1 1/2".

Where are you located? With a 2.5 GPM shower head you should be just fine with a 1 1/2" drain, but of course, codes are codes (and rules are meant to be broken )