What kind of lumber do I use for my house support beams?

You can replace support beams but you must first support the floor joist that are sitting or attached to them.

2" X 6" X 14 feet does not sound like a support beam. That even is small for floor joists. Most floor joists spanning 12 feet are at least 2" X 8" and often 2" X 10".

Are you referring to support beams or floor joists?

Floor joists are usually spaced:

16" on centre (There would be about 14 1/2" between the joists)

12" 0n centre (There would be about 10 1/2" between the joists)

If the "beams" are actually floor joists, you can place a new joist of the same size along side of the original floor joist and nail it to the old joist.

You want lumber with very few knots and no large knots.

Make sure you fix the water problem first or your money and work will be wasted.

If there are any pipes or wiring going through the joists/beams, they must be removed first; then replaced once the joist/beam is done.

Always crown your wood. Crowning is done by looking along the edge of the wood (2" or 1/1/2 " edge). Most pieces of lumber are not perfectly straight. You want the bend in the lumber to be up in the centre so you mark an arrow with a marker pointing in the direction where the lumber is bowed up. Make sure when you install the lumber that the arrow is up.

But construction grade spruce or better lumber that does not have any large knots; it can have some small knots that are not grouped to-gether; and is not too bowed or twisted; and not split and no rot.

If you cannot find good lumber at home Depot, Lowes, then try a Lumber Yard. You may pay a little more but the lumber should be good.

Always check the lumber before taking it.

You can try lumber yards which may have better quality grades of lumber or engineered wood products with no defects but having some knots are acceptable. Replacing the whole beams may not be possible since subflooring is attached to it. An easier option would be to add lengths of similar or larger size boards in the damaged area...a method called "Sistering" where a section of new 2 X board is glued and nailed or screwed alongside weak or rotted areas of existing beams.Just make sure the floor or old beams are level or straight before nailing / screwing new sister boards in place....jack up sagging areas if needed. And use lengths of new boards that will extend at least a few feet on either side of the damaged area...or wider boards like 2 X 8 which have more strength than 2 X 6 if possible...notch out any areas which may need to be 2 X 6 in width. Another option is to cut 3/4" plywood into 5-6" strips and glue /clamp together to make it 1 12" thick...then glue and screw in place as a sister...plywood being stronger than plain lumber but limited to 8' lengths

Videos and links on sistering methods....

https://www.google.com/search?q=92+jeep+cherokee+s...

https://www.google.com/search?q=92+jeep+cherokee+s...

get some bids for this support and replacement -- that way you know those costs and can better understand what needs to be done to shore up the kitchen floor = it is possible that what is in place needs concrete block under the new support uprights and you could sandwich 2" by 10inch treated boards for the best support .... if you are not dealing with a basement [finished] room or if you are pier & beam under the house it is a relatively easy job to shore up existing everything ..... getting some quotes/bids will get you the best results and help you reach the true repairs .............

You can't replace support beams really only support them. You desperately nerd to hire a contractor.

#2 or better Douglas Fir or Southern Yellow Pine. Doug fir is about half the weight of SYP, but the pine is more dimensionally stable so it won't swell and shrink as much. Tell them what you need. 2x6 should be fairly easy