[bnjmn]

On any macOS computer (or replace /usr/share/dict/words with your own word list):

  grep '^[qwertyuiop]*$' /usr/share/dict/words | \
  awk '{ print length(), $0 }' | \
  sort -n

[juujian]

Works for Ubuntu, too. My Colemak self can only get fluffy (6) from the front row, that's the longest word. Middle row really shines though, I can get hardheartedness (15) or assassinations (14).

[tiltowait]

Interesting that your dictionary doesn't have "tenderheartedness", which is two letters longer.

[jmholla]

"tenderheartedness" uses every row, not one row.

[cbsks]

Not on a Colmak keyboard

[seabass-labrax]

Gulp, fluffy puppy pug! Yup. Fly, ugly pup, fly.

I note that hardheartedness and hotheadedness threaten the darnedest nonstandard assassinations. Such sordidness!

[travisgriggs]

Nice.

Middle/Second row result is

8 flagfall "Flagfall, or flag fall, is a common Australian expression for a fixed start fee, especially in the taxi, haulage, railway, and toll road industries."

8 galagala "A name in the Philippine Islands of Dammara Philippinensis, a coniferous tree yielding dammar-resin."

Lower/Third Row: - None

There are no vowels on the bottom row. So no words. I've been typing at ~ 50wpm for 30 years, and I don't think I'd ever actually consciously recognized this fact about the bottom row.

(standard US keyboard layout)

[JoshTriplett]

For QWERTY, I found two nine-letter words using only the middle row: halakhahs and haggadahs.

And yeah, nothing in the bottom row other than acronyms and similar pseudo-words.

[Symbiote]

Dvorak:

  ',.PY FGCRL   pry or Lyly
  AOEUI DHTNS   tendentiousness
  ;QJKX BMWVZ   xxxv, www, bbq or mm

After 'apt install wbritish-insane'

  pyrryl (a chemical group)
  unostentatiousnesses (and anaesthetisations is good too)
  mmmm

[tedunangst]

Knuth vs McIlroy all over again.

[IshKebab]

Just use https://www.visca.com/regexdict/