If there was, just about every B&B in the country would be in trouble.
I am not sure about code, (I’m not a code inspector ;)), but as long as it is installed correctly, with proper venting, I would only advise the client of the maintenance required to maintain safe operation.
If certified to ansi z21.50 no problem.
Usually direct vent type or marked on the name plate stating
ALSO CERTIFIED FOR INSTALLATION IN A BEDROOM OR BED-SITTING ROOM
2006 IRC G2406.2 (303.3) Prohibited locations. (Gas) Appliances shall not
be located in sleeping rooms, bathrooms, toilet rooms, storage
closets or surgical rooms, or in a space that opens only into such
rooms or spaces, except where the installation complies with
one of the following:
The appliance is a direct-vent appliance installed in
accordance with the conditions of the listing and the
manufacturer’s instructions.
Vented room heaters, wall furnaces, vented decorative
appliances, vented gas fireplaces, vented gas fireplace
heaters and decorative appliances for installation in
vented solid fuel-burning fireplaces are installed in
rooms that meet the required volume criteria of Section
G2407.5.
A single wall-mounted unvented room heater is installed
in a bathroom and such unvented room heater is
equipped as specified in Section G2445.6 and has an
input rating not greater than 6,000 Btu/h (1.76 kW). The
bathroom shall meet the required volume criteria of Section
G2407.5.
A single wall-mounted unvented room heater is installed
in a bedroom and such unvented room heater is equipped
as specified in Section G2445.6 and has an input rating
not greater than 10,000 Btu/h (2.93 kW). The bedroom
shall meet the required volume criteria of Section
G2407.5.
The appliance is installed in a room or space that opens
only into a bedroom or bathroom, and such room or
space is used for no other purpose and is provided with a
solid weather-stripped door equipped with an approved
self-closing device. All combustion air shall be taken
directly from the outdoors in accordance with Section
G2407.6.
2006 IRC G2406.2 (303.3) Prohibited locations. (Gas) Appliances shall not
be located in sleeping rooms, bathrooms, toilet rooms, storage
closets or surgical rooms, or in a space that opens only into such
rooms or spaces, except where the installation complies with
one of the following:
What ever codes you are using it all boils down to proper venting and flame safety i.e. pilot or flame recognition system such as a thermoplie or thermocouple.