I want to hard wire a smoke alarm and co alarm in my wheel house, where is the best spot to mount them. Ceiling? Wall? How high? Close to or away from heater? Thanks guys!!

I would put it away from the heater and then mount it per the guidlines of the unit. I think like six inches from the wall or ceiling.

They make 12V ones?

Yeppers, they make em for rv's.

I don't know about a fish house but in my camper it is half ways between the top of the door and the ceiling... that is the way it came

As you probably guessed the smoke alarm should be high in the house because warm smoke will rise to it quickly. The CO detector is a little different though.

Air has an average molecular mixture weight of 29 while pure CO is almost the same at 30. There isn't enough of a difference to matter so the CO doesn't rise to the ceiling or settle to the floor (like Carbon Dioxide) it blends in evenly so it doesn't matter how hi or low you mount your detector.

However, when I mounted mine the directions said to keep it 10 feet away from the heater.

In my 17' house, the forced air furnace is mounted at the rear blowing forward. I have the CO detector mounted on the front wall about half way up pretty much in the path of the air flow. So far, no false alarms, and thankfully I'm still here

For the CO detector put it in your breathing zone where ever your head is going to be Ie: if sleeping head level!

The manufacturers spend a lot of money designing and testing these units to be sure nobody dies. The last thing they want are lawsuits. With that in mind, I wouldn't do anything other than what the manual indicates.

Co detectors (home use) rarely tell you where to put them as the area and time is pretty flexable as it is a cumulative exposure
"70 ppm CO Concentration 60 – 240 minutes
150 ppm CO Concentration 10 – 50 minutes
400 ppm CO Concentration 4 – 15 minutes

Where by my handheld device alarms at 35 PPM
Where To Install Your Kidde CO Alarm
The following suggestions are intended to help you with
the placement and installation of your Kidde CO alarm.
• Place out of the reach of children. Under no circumstance
should children be allowed to handle the CO alarm.
• Install in a bedroom or hallway located close to the
sleeping area. Take special care to verify the alarm can
be heard in sleeping areas.
• It is recommended that a CO alarm be installed on each
level of a multilevel home.
• Locate at least 5 feet away from all fuel burning appliances.
• Placing at eye level allows for optimum monitoring of
the red and green indicator lights.
Installation Instructions (cont.) Features and Operation
5 6
• Insure that all vents of the unit are unobstructed.
• Do not install in dead air spaces such as peaks of
vaulted ceilings, or gabled roofs.
• Do not install in turbulent air from ceiling fans.
Do not place near fresh air vents or close to doors
and windows that open to the outside.
• Keep the CO alarm away from excessively dusty, dirty,
or greasy areas such as kitchens, garages and furnace
rooms. Dust, grease and household chemicals can
affect the sensor.
• Keep out of damp and humid areas such as the
bathroom. Avoid spraying aerosols near the CO alarm.
• Do not install in areas where the temperature is below
40° Fahrenheit (4.4° Celsius) or hotter than 100°
Fahrenheit (37.8° Celsius).
• Do not place behind curtains or furniture. CO must
be able to reach the sensor for the unit to accurately
detect carbon monoxide."
quoted from Kiddie

so I go back to my statement put the detector where your nose may be cause thats how it gets in your body!