Register vent size (and hole size) for small bathroom

We live in the Northeast and have an approximately 8x4ft 1st bathroom with one outside exposure on the first floor of our house.
We have gas-fired forced air heat but interestingly, the bathroom currently does not have any registers.
We are thinking of adding a register which will require cutting through a marble tile floor, so before we cut we want to make sure we are doing the right thing...
1. A heating contractor suggested a 2x12 inch register to be placed on the floor an inch or two back from the outside wall.
Does this sound like the right size and placement for a register for that size room?
2. If we go with a 2x12 inch register, is that the exact size that we should cut for the hole through the tile or do we need to leave a "little extra" room?
Thanks, Jeff
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I will cede to the HVAC guy on the correct size. I would use a 4 x 10 because they are easier to find and miss obstructions with. I suggest you buy the boot before you cut the hole. Then cut for what you bought. I usually add 1/4" to the width and length of the boot for the rough cut. This will be some tough cutting and you better make sure you are clear of the joists below the floor before you start.
Is the bathroom cold? Or why do you want to add a vent? My 4 x 6 half bath doesn't have one and it has never been a problem.
Colbyt
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Very difficult for someone here to see your home and what you have. I would suggest your local man is likely right.
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Yup..what did the manual D say for the bathroom? You DID get a room by room manual J calc complete with D calculations didnt you?
if not.... Woah...another hack finds a customer.

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Jeffrey J. Kosowsky wrote:

Sounds like a standard placement and a standard size. If this is on the first floor and you can easily get to the underside and place the duct where ever you want, I would think twice about cutting through the marble floor. One possibility is to put the duct in through a cabinet with the the register vertical (2 inches high) in the kick space. Not only would this direct the on you, but the register would be hidden. A bathroom is not like a regular living space where you need registers under the windows for long term comfort. Typically you use a bathroom for only a short period increasing the heat only when you take a bath or shower. 24 square inches is a lot but most likely you will have it turned down 1/2 or 3/4 most of the time.
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This is Turtle.
First I think a vent in a bath room is a mistake in the first place. What happens is when your running you heat and have a bath room heater on. It will pull the heat out of the bathroom to cool it off. Then if you have cooling on the system. You then have 55 to 60F air blowing on you when you get out of the Shower. You may be alright with just heat onthe hvac syatem but cooling on it, it will give you some problems.
Now of cource there is all forms of thoughts on this and it may be just what you would like.
TURTLE
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