I will be moving into a new house in a month. First few things I want to do is to make simple changes to the existing doors to "harden" them up before getting more quality doors all together. Aside from new deadbolt, strike plate, U pin type look on the interior, I would like to use longer screws to secure the door into the frame studs. Looking around I see the general recommendation is 3" or 4" deck screws, however I see some suggest drywall screws.

What do you recommend?

Also, this is my extreme attention to detail kicking in, but is there a preferred brand of deck screws that are stronger or have better features than others? If so, can you post a link to the specific deck screw?

Thanks

I"ve just always used 4" deck screws from Lowes. I'll buy 4 lbs at a time, and try to use them whenever possible. I'd avoid drywall screws, they tend to by much weaker and can be brittle. Keep in mind, the weakest point on your door isn't the hinges or the latch plates, its the wood all of those things are held to. They sell door reinforcement plates that help strengthen things up considerably. I swear there was a thread here just a few days ago about them.

This is what you seek.

http://armorconcepts.com/

Screws suck for shear strength. Rule of thumb is screws go vertical, nails horizontal. It would take a lag bolt of some sort to come close to the shear strength of a common nail.

This is correct for general construction, but a door experiences more than just shear forces. Screws have about 60-70 % of the shear strength of a similarly sized nail. But screws typically have about 4x more pullout strength. While a door being kicked in might experience shear forces, it is also experiencing pullout forces as the door is likely to flex inward and pull away from the wall, at an angle. Use enough screws, and you wind up with a very strong mount. Also, a door held in with nails is likely to start pulling hinges out of the walls over time.

By the numbers below, it would take less than two screws to exceed the strength of a single similarly sized nail. But, you could probably use BOTH to your benefit, dill extra holes in your hinges and latch plates, and add two nails to each. Classic example of the ar15.com do both.  

Examples:
16d nail:
    Diameter: .162"
    Shear Strength: 138 Lb  
    Pullout Strength: 40 Lb
#8 Screw:
    Major Thread Diameter: .164"
    Shear Strength: 90 Lb
    Pullout Strength: 168 Lb

Go to Home Depot.  Find the screw aisle.  Look for the name Spax.

Find some 14x3-1/2"  or 14x4" flat head screws.

Go to the tool area.  Find a Countersink big enough for the heads on the #14 screws.  Find a 5/32" drill bit for the pilot hole - so the screw does not split the 2x4 behind the door case.

Takes very little time to fix the problem for good.

There is more than just drywall screws on the market. IMHO, drywall screws blow; I used to buy them for all my projects because they're cheap, but that was when I was young and dumb. I don't have too many left anymore. I primarily use construction screws, which are much stronger. When I need even high load I go for the Spax mentioned above. The Spax screws are made of high-strength steel and are rated for shear load even higher than that of nails. Spax is what was used to sister 2X12 floor joists together in my house when removing 2 load-bearing posts near my stairs. They are incredible screws.

Thanks for the input.

Looks like the countersink size required for #14 a screw is 1/2" according to this link - https://www.boltdepot.com/fastener-information/Wood-Screws/Wood-Screw-Pilot-Hole-Size.aspx

You are welcome.  I use the Spax stuff for heavy loads.  Here is the countersunk range:

http://spax.us/en/multi-material-construction-screws/unidrive-flat-head.html#.WV5Ub4WcGUk

I prefer to use the square drive, but the #3 phillips part of the head works too. Just don't try to drive them with a #2 tip.

Around here lots of homes have a self closing fire door from the attached garage.  The stupid hinge screws wallow out the holes because they are heavy & slam all the time.  It takes me about 45 minutes start to finish including vacuuming up the drill chips to do a 3 hinge door.  Generally I use 3" screws on the door itself, and 4" screws in the jamb.

Of course you still want reinforcement plates at the strike. Use #12 screws in the strike plate reinforcement mentioned above.

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Use only heavy steel screws, plated. Drywall screws are pretty brittle and I think that they are cast metal and they rust very quickly.

ETA - I have to often remove old drywall screws that the previous owner used in several places around my house. They were all very badly rusted and most broke off in the hole. Older flathead steel screws all came out in one piece.

Good info here. I just ordered 3 sets of the EZ Armor (or whatever it's called now) door kits today.

Very good info, now what to do to re-enforce the windows that are on either side of the door and all around the house... If someone wants in bad enough they'll just make a couple whacks on the window and hop in that way unfortunately.

Since you are planning to replace the doors anyway, why not go ahead and remove the trim around the door so that you can get a good look at what the door is mounted to.  You can use brads to re-attach the trim when you are done.  You might be surprised what the builder did.  I certainly was.  There's no point using 4 inch screws if you only have 3 inches of wood to screw into.