There's more to changing between induction and gas than just the length. No matter what, it's highly unlikely that you'll find one that actually fits the cutout. If you seriously think changing is a possibility, make sure to save scraps of your counter top material, backsplash tiles and any other materials you're using, so that you can fill in the hole a little and cut to fit the new cooktop. Often, when old appliances die and new ones are put it (which aren't the same size at that future date even if the equivalent models at the time the first one was bought were exactly the same), the installer will make a trim out of wood or stainless or whatever you want to fill any gaps. I've seen this done several times, and you have to really look to notice it.

Obviously none of the people who have responded have even a remote clue about how to properly size a line. When designing a potable water distribution system you begin by selecting all the end use fixtures to determine what the end use load will be. In the case of the original post they want a shower head, body sprays, a hand shower and possibly a rain shower head. Quote:"How many fixtures will you have on at any one time? Remember that 3/4" pipe has double the capacity of 1/2" pipe." Code requires that we design a potable water system for a worst case scenario. The system must be capable of maintaining the code listed minimum fixture "Dynamic head pressure" even when every fixture in the house is turned on at the same time. The statement that a 3/4" pipe has twice the capacity of a 1/2" pipe is not true. The capacity, or properly the volume of flow is determined by the size of the metering orifice in the end use fixture. It is true that a 3/4" line has double the cross sectional area of a 1/2" line however both will supply the same volume, the difference being that the velocity of flow will be twice as fast in the 1/2" pipe. The problem here is that as the velocity of flow increases the "fiction head pressure loss" increases dramatically. In addition to the loss of pressure due to friction head if the velocity of flow exceeds 8fps we start seeing sever pipe wall erosion, which leads to premature pipe failure. In fact, while acidic water is the leading cause of pin hole failure in copper pipe, excessive velocity in undersized pipe is the second leading cause of pinholes. Preferably we should have the end use fixture data available when designing the system but in situations where that information is not yet available we use the gal/min flow rates that are published in the code. Now getting back to the original question. All the end use fixtures in question are types of shower heads and per code shower heads are restricted to 2.5gpm so let us begin putting it all in perspective. Using the code standard of 2.5gpm we get shower head (2.5gpm), hand shower (2.5gpm) and body sprays (2.5gpm)equals and a hand shower(2.5gpm) for a total load of 10gpm. Consulting the "Type L Copper Friction Loss Table" we find that if we supply this shower with a 1/2" line the velocity of flow would be 13.80ft/sec and the pressure loss would be 67.72psi/100ft of pipe. If we increase the pipe size to 3/4" the velocity of flow is 6.62ft/sec and a pressure loss of 11.17psi/100ft.

If you are happy with something under 300cfm, and more noise, you can use the 4 inch. You aren't going to 600cfm, even with 6 inch. If you have a fan curve (cfm vs. static pressure), a calculation can be made. Do you have a make/model for your hood/blower?

I bent the tabs in on my filter holder so it would hold a 4" filter instead of just a 1". I think it gives a bunch more surface area of filter media which should help lower the static pressure. I could hear it build suction as I slid the new 1" filters in place when new and it was horrible after a month and no one here smokes and we don't burn candles. I slid the 4" filter in and could barely hear any change in the air noise. I still do not see waiting a year to change it like the wrap said, that is nuts. I think 4 months is a good interval and go from there. If you can make a 4" filter fit I would sure do it, especially if the filter media is pleated.