Ready for ceiling and heat. Is this ok?

[sideways]

As money was available this summer, I've studded the interior walls of my 30x50 metal building, run electricity, insulated the side walls with R19 and put up paneled walls. The ceiling is 10ft high and it has concrete floors with two garage doors. I know this has been discussed multiple times on various threads but, I beg your indulgence. Here is my plan: My trusses are
4 ft apart and I plan to staple 3 mil plastic to the bottom of my trusses as a vapor barrier. Next, I plan to screw 12ft long metal sheets (similar to those on the outside of my building) directly on the plastic sheets. Finally, I will lay R30 batts of insulation in the ceiling on the plastic, which will be supported by the metal ceiling underneath. Lights will be attached to the metal ceiling.

Question 1; will that be sufficient for preventing moisture and providing adequate insulation for my heater? I plan on suspending a 75K Mr. Heater in one of the back corners.

Question 2; I know the Mr. Heater is 120v and about 6 amps according to the manufacturer...is 14/2, 14/3, 12/2 or 12/3 best to use? It will be on its own circuit...should it be 15 or 20 amp? I'm obviously not an electrician. Thanks to all the "experts' on this site...appreciate the advice.

 

[bloodvette]

I've always been told 6mil polly should be the bare minimum 10 is preferred... I have a general contractor I work for who insists on 10 mil becuase he's opened up a lot of walls and found mold due to thin/torn poly.

I am an electrician, you said a "75k heater"? based on 6 amps at 120V that will produce approximately 750Watts. which is very little. I have a 10kw heater in my infloor, a lot of houses have 20-30kilowatt heaters, so a .75kW is what you would chose for a baseboard heater in your bathroom if it gets a little cold in the winter... no where even close to adequate.... but in the event you decide to run a dedicated circuit for it, you are fine with a 14/2 wire for that particular described device. 14/2 is good for 15 amps however the breaker should be loaded no more than 80% which means 12 amps, so your only 1/2 way loaded on that circuit which is a good place to be.

 

[gregsrt]

He didn't mention the Mr Heater is a natural gas 75k btu unit, not an electric heater. The fan runs on 120V. 14/2 is what I ran for mine.

I agree with the bloodvette on the poly, thicker is better. Its also easier to work with.

 

[sideways]

Thanks. I've already hung the 3 mil on the side walls so it is what it is now. I will look for heavier mil plastic for my ceiling. I was hoping that the configuration was correct and would work...if I use the correct mil plastic. Sorry for the confusion...I was referring to a ceiling mount 75K btu Propane Mr. Heater and I do intend to put it on its own circuit. I will plan on using 14/2 wire and a 15amp breaker. Thanks again.