Do the insert fittings restrict the flow that much? It seems like it would a lot. The 3/4 poly fitting inside diameter almost seem like 1/2 pvc to me. Does it even matter? I'd rather go bigger than smaller.
Nope. The velocity increases to compensate for the smaller cross sectional area which translates to more friction loss(minor) and more noise. One uses a larger pipe diameter to increase the cross sectional area and decrease friction loss(pressure loss) when installing long lengths of pipe. Each fitting also contributes to the loss of pressure through friction loss and with many fittings over a longer length a larger diameter pipe is necessary. If you can afford it always use a larger pipe because it decreases the noise of your system. That's about it. JMHO Aloha
Bigger it is- it's not much more anyway. Thanks