We went with a 42 inch side by side but it has not yet been installed. I did not have room for a larger refrigerator but would certainly have gone larger if I did have the room. 36 will not be large enough for you. We are also a family of 4 (with older kids) and if you think refrigerator space is tight now, just wait until those little ones hit puberty and start eating up a storm. Go with the largest fridge you can fit into your space. You won't be sorry.

Go with the 36" all ref built in with a magnificent 23 cu ft of refrigerator if you want more ref space. The 36" integrated all ref weighs in at 20 cu ft. Even the 48" sxs has 19 cu ft of refrigeration space. The 36" over and under has 16 cu ft.

Alternately, some people have ref drawers for cooking supplies near the prep area - butter, milk, eggs, veg sorta thing. Some people add undercounter beverage center refs to get the wine/beer/soda stuff out of their normal ref.

If you need more mostly for party storage - or perhaps you use a lot of fresh ingredients that need refrigeration, you could always place a Frigidaire Commercial all ref in the pantry - 19 cu ft of completely tray space. And get something nice for out front use.

We have a small kitchen and there are just the two of us but we have a 48 side by side. I am amazed that we really do need the space and keep it quite full. We eat lots of salad and vegetables and they take up a lot of space. And the top is filled with bottles of seltzer, tonic, iced tea. Bread, yogurt, cheese -- it is crammed, always. It very much depends on how you eat, how you cook. We could never get by with anything smaller. I'm always wonder why a 48 range is such a popular choice as we never have a need for more than the 30, but there are loads of people who are totally happy with a smaller fridge and could never imagine needing the 48.

Is the frig in the mudroom a frig/freezer, or just frig? If it's both frig/freezer, I would think the 36" built in bottom freezer would be fine. If it's only a frig, I'd be worried about freezer space. Those bottom freezers don't hold enough, in my opinion, for a family of four. But maybe I just have too many quarts of ice cream in ours!!! We have the 24" thermador frig and freezer columns, along with undercounter frig drawers. This is the perfect amount of space for our family of 4.

I have three kids and a DH. I have a 42" counter depth side by side thermador. We cook every night and shop bi-weekly. I am able to get everything that I need in it. I do have a seperate deep freezer though for all of my meat b/c we grow and butcher our own.

We bought our 30" fridge and 30" freezer set in anticipation of our reno over 3 years ago which we put into service in our garage. We have an older s x s in our kitchen as well. When we renovate, my husband says we should get rid of the old kitchen one since it is inefficient, but that freaks me out as I "need" all the space we currently have (not really, but I do love it).
Our fridge and freezer each have 17 cubic feet of space.

I have 2 young sons, 7 & 8.5, and know they will eat even more when they hit their teen years. Add in their friends and the occasional party and the need for more than a regular size fridge becomes clear. I love how I can put a pizza box in my fridge (or several) and have room to spare on each side. When Costco messed up and made 2 of their huge sheet cakes for the same day a few weeks ago (2 little league parties, a day apart), the guy there was shocked when my husband said he'd take both home the same day and save a trip back.

I would rather give up the space for other things than my refrigeration space. Ours are Energy Star rated, so probably no more power sucking than a smaller non-Energy Star fridge.

You know your own needs best. Comparing cubic feet is only the first issue. Different fridges are organized differently and will hold more or less of your actual stuff depending on how they're designed. If you don't have a good handle on what's in your fridge when it's full, take daily pictures for a couple of weeks, morning and evening, so that you capture the new groceries as well as the containers of partially prepped, fully prepped, cooked foods, and leftovers. Don't forget the doors.

Do you love gallon jugs? If so, do you love having them in the door? Or do you want them colder and on a shelf. Do you want your shelves deep enough for a platter or shallow enough that you don't lose stuff in the back? Do you love specialized compartments, like an egg keeper, deli drawer, 2 liter cradle? Or are those wasted space gewgaws to you that make it difficult because they don't hold enough or are in the way?

Go to the appliance showrooms and try them all out. Compare your pictures. Measure your food if you have to. Choose the fridge that actually works for you.

Also, assess freezer space. Do you freeze food you've cooked? Or want to? I was brought up with the idea that it's just as easy to cook two chickens as one, and with a really good freezer that makes instant meals for when you don't have the time or inclination to cook. Lots of foods freeze really well. If that sounds attractive, maybe you need an all fridge and an all freezer, instead of two fridge/freezer combos. Unless you have dual compressors (I think you were originally talking about SubZero, which does have them), separate units work better. If all of that sounds dreadful, maybe less freezer space is the way to go.

My own idea of what someone in your position might need if you shop infrequently, live in a warm climate, and/or entertain large groups, is a 36" over/under SubZero, a spare fridge with minimal freezer space, and a full sized freezer. If you cook less and shop more, then the 36" plus a full sized spare fridge with a decent sized freezer should be plenty.

But then we get to what you want. Do you want a 48" fridge? Do you prefer a side by side to an over under? Are water and ice dispensers important to you?

Back to what I said before. You have to choose your fridge to suit your own needs and desires.

(Just for comparison, I decided against SubZero because I didn't like the current layout, and especially how deep the door shelves were. I got Miele 30" all fridge and all freezer, 24" fridge drawers which hold standing tall bottles for prep, and my old coil shelf upright freezer in the garage.)

pllog is absolutely right. Each refrigerator is different.
I nixed Subzero integrated 700 series in the size that I needed because it had very inadequate produce bins. Their Built ins had much nicer bins in the size I wanted. But I did NOT want the built in with the grill/cover showing on the top.

I nixed Miele because it did not hold gallon jugs in the door. (completely the other reason from pllog) We prefer our milk in the door because of the kids. It is easier for them to get the milk out.

We ended up getting Thermador Freedom column because I wanted fully integrated (not built in) and was able to hold milk jugs in the door AND had enough produce storage.

Their is also the certain build quality. I thought some "built in" brands did not look very nice inside. They used the same bins you see in the cheap models.

Built ins look different from Integrated fridges. You also need to decide if you want Built in or Integrated.

Do you have someone come in and cook for you? Do you cater parties at your house? Do you have large family get togethers where you have to prepare dishes in advance? I know many families that are the same size/age as our family and they have more than double the refrigerator/freezer space that we do. Each family's need is unique.