maximizing flow from tub spout

[Bette]

My husband and I are remodeling a bathroom which will have a shower over large (70 gal) whirlpool tub and want to maximize the flow rate on the spout for the quickest fill possible. We can not use a roman spout do to type of tub (alcove with no room for spout) hence it will be a traditional wall mounted filler. We have 1/2 inch copper pipe going to the bathroom on the second floor. Water pressure is good. Kohler has recommended their rite temp valve with a twin ell to maximize the flow. They said to connect a 3/4 inch copper pipe between the valve and the spout. This is much more costly than a standard valve. Any idea if this will really increase the flow rate to the spout? Any other suggestions?

 

[Reach4]

How practical would it to be to run a bigger hot water (only) line to the tub?

I don't know how the valve affects the flow. If Kohler thinks it is significant, I would think they have a reason other than trying to sell you a more expensive valve.

I suspect that the hotter your water is, the more important the bigger spout and valve would be. Why? Because if the fill is all hot water (not uncommon), the hot supply pipe carries all of the water. That will be a limiting factor. If the water is hot enough to mix significant cold water, then the cold pipe will carry part of the water. Now you may have to have a mixing valve to limit the temperature out of the spout. But if you must have a thermostatic mixing valve, you could put a thermostatic mixing valve at the bathroom fed by 150 degree hot water. Then you would have less drop through your existing pipes. You would need another thermostatic mixing valve for the kitchen or other hot faucets. If your only mixing valve is at the hot water heater, the common cheaper solution, then the hot water supply pipe diameter is more critical.

 

[Sponsor]

 

[hj]

They do NOT make a "3/4" twin ell", in fact a twin ell has severely restricted openings to prevent shower operation when the tub is filling. The tub flow will be completely dependent on the size of the openings in the valve, and because most modern valves are quarter or half turn, the openings are fairly small, even with a 3/4" valve.

 

[Jadnashua]

Sometimes you have to dig deep, but most spec sheets do list maximum flow rates of valves. Once in awhile, to get that, you may need to call the manufacturer. 6-8gpm is about normal for a 1/2" valve. A few 3/4" ones I've seen can go up to about 17gpm.

All of those specs are based on a specific pressure range...outside of that, it could be higher or lower. A roman tub spout may not actually have great flow rates...it all depends on what is used to connect it to the valve and what size its internal passageway is.