You will need to cut into the brickwork and install them to comply with local building regulations.
Yes vents can be in the floor instead of the wall.
Return air vents.........
Cold air return vents are the ones on the wall
No sunlight reaches that depths, although if you go far enough down there're hydrothermal vents which in return heat things up.
No. Doors will suffice.
Gable vents go on the ends of the house where the peak is. At the top point of the triangle.
In my opinion where the supply vents are located is not as important as where the return air vents are located. the supply vents should be located towards the outer walls if possible. the return air vents should be located towards the center of the dwelling if possible. every effort should be made to get the return air vents as high as possible on the wall , if not in the ceiling.Remember you are trying to get the warm air back to the a-coil so it can be pumped outside through the refrigeration lines to the condensing unit. if the ductwork is used for heating also you should put some return air vents down low to get the cool air to the furnace. This is my personal opinion and may not be everyones.
Hydrothermal vents can get very tall. Many of them are as tall as a three story house.
Return air vents in each room (none in bath or restrooms) sized for the amount of cfm needed for that specific room are best but if this is not possible then pick a central location and return vent should be sized for total cfm required of house.
Cose the high vents in the winter and low in the summer..
The average number of HVAC vents in a house can vary depending on factors such as the size of the house, layout, and HVAC system design. However, a typical house may have around 8-12 vents spread throughout different rooms to ensure efficient heating and cooling distribution.
Around 34% of house fires are caused by clothes dryers, with the majority of these fires being caused by dirty or clogged dryer vents. Regular cleaning and maintenance of dryer vents can help prevent fire hazards.