What are some songs to play on the piano for background music for a housewarming party?

Great balls of fire

Elvis Presley. Maybe the song I Can’t Help Falling In Love With You.
The Carpenters multiple songs
Neil Sadaka multiple songs
Captain and Tennille multiple songs
Elton John Multiple Songs
Billy Joel Multiple Songs
Beattles multiple songs
Led Zeppelin Stairway to Heaven
Simon and Garfunkel Scarborough Fair
Madonna Isla Bonita
Lady Gaga Alejandro
Enrique Iglesias I’m Your Man
Mamas and the Papas California Dreaming
Music Box dancer (I think Frank Mills did it, not sure).

Try some early Jim Beckman.

Check out this Songs About Homes and Houses list.

La Vie En Rose
It Had To Be You
My Romance
Your Song

How about some jazz standards?

Almost Like Being in Love
April in Paris
Mack the Knife
Can’t Help Lovin’ That Man
Do You Know What It Means to Miss New Orleans
Fools Rush In
The Lady Is a Tramp
Misty
Mood Indigo
Satin Doll
Smoke Gets in Your Eyes

A cheeky little number

Meatloaf!

Our House by Crosby Stills and Nash.