And if so how big of one do I need for a 6x12 with a v front and also it does have a 6'6" ceiling height and the floor is insulated if it makes a difference or not I don't know?

I've had a ventless heater in my drop down house that I built about 15yrs ago. My windows frost up over night, I don't know if that is because of the ventless heater or not. Other than that I haven't had any problems. That's just my experience.

The newer ones are safer than the older ones. I would install a CO detector and leave a window cracked just to make sure, tho.

Being non-vented you will build up some moisture inside. This is something you will have to contend with. During daytime hours when people are opening doors and such quite often it's not as much of an issue.

I have a 10,000 btu "Outdoorsman" made by Ruddy. It works great on my 7 x 12 and I rarely take it off it's lowest setting, even on the coldest days.

I have used them for I don't know how may years and am still here. But you must make sure you have a CO detecter but thats a given in any fish house, and the only problem Is the moister like said above. Am going to try to put dehumidifier in my fishhouse this year to see if that helps at all.

I have one and no problems here. Just like the other guys said, bring a battery powered CO dector and you will be fine!

H2O is a product of combustion. So yes, the moisture is a result of the ventless heater. Considering how dry the air is in winter, I would welcome the added moisture.

It's a welcome until water is dripping off the ceiling and the windows have as much is on them as the lake....

As far as being safe, well they are probably your safest option for heat, but common sense is still needed...

In my opinion a vented heater is the way to go for safety. I do agree that a CO detector would be a must for me especially if I planned to sleep in the ice house. My heater is a direct vent and I still have a CO detector in it. If I were using a ventless heater I would have vents going directly to the outside.

We have vent-less in our house. We added vents in the wall (on each side) for cross ventilation. We didn't have any moisture problems on the windows or the ceiling. If you install good quality insulated windows, you won't have a problem. No matter what, always have a CO detector. Some houses that I have seen and been in are built too air-tight. The house can't breath, trapping any moisture that is in it. Build your house to breathe.

I actually have sliders on each side of the house This would be plenty sufficient I would think agree????