Does the ONT’s Wi-Fi cover my entire residence?

No.
Wi-Fi signals experience attenuation due to distance from their source just like any other radio. This signal attenuation subsequently causes the radio to be less effective and throughput suffers. Eventually, connectivity is lost when the signal becomes too weak. There are essentially two factors that affect signal attenuation between the access point and the client, and those are range (or distance), and attenuation due to obstructions
 

Building Material 2.4GHz Attenuation 5 GHz Attenuation
Free Space Range • • • • • • • •
Solid wooden door • • • • • •
Hollow wooden door • • • • • • •
Steel or fire exit door
Concrete Wall (double brick) • • • •
Concrete Wall (single brick) • • • • • •
Reinforced Slab in double storey • •
Single Pane Window • • • • • • •
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Category: 
Speed & Connectivity