Ventilation Question

[Nature]

I have not installed one, yet, but have researched in preparation of.
Recommend 20-30 air changes per hour. Also may want to consider if you will have additional guests smoking in there at the same time.
At that rate, some sort of fresh air return is highly recommended, and probably necessary if you have combustible heat sources in the home (gas water heater, furnace, fireplace).
They make fresh air returns that either only turn on when the exhaust is running, or reach a pressure differential limit. You would not want 100% equalization exchange in order to maintain that negative pressure to prevent smoke odor spreading to other areas of the home.
You could get away with cracking the window, but that is probably not to IBC.
Next consideration is your comfort level and efficiency. If you are exhausting air at a decent rate with fresh air intake, you will be pulling in whatever climate is outside, whether that be cold, hot, humid or whatever. You could do a heat recovery exchanger, but they are pricey and I doubt would offset any extra energy spent for heating/cooling your home or room any time soon.

For my room I am contemplating converting, which is about 1/2 the size of what you describe, I was considering about 1450 CFM, but I was also planning on about 3-4 smokers in a more confined space. I also tend to over engineer some things.

[SoCal gunner]

I have not installed one, yet, but have researched in preparation of.
Recommend 20-30 air changes per hour. Also may want to consider if you will have additional guests smoking in there at the same time.
At that rate, some sort of fresh air return is highly recommended, and probably necessary if you have combustible heat sources in the home (gas water heater, furnace, fireplace).
They make fresh air returns that either only turn on when the exhaust is running, or reach a pressure differential limit. You would not want 100% equalization exchange in order to maintain that negative pressure to prevent smoke odor spreading to other areas of the home.
You could get away with cracking the window, but that is probably not to IBC.
Next consideration is your comfort level and efficiency. If you are exhausting air at a decent rate with fresh air intake, you will be pulling in whatever climate is outside, whether that be cold, hot, humid or whatever. You could do a heat recovery exchanger, but they are pricey and I doubt would offset any extra energy spent for heating/cooling your home or room any time soon.

For my room I am contemplating converting, which is about 1/2 the size of what you describe, I was considering about 1450 CFM, but I was also planning on about 3-4 smokers in a more confined space. I also tend to over engineer some things.

Great info here. I'm really hoping to avoid the fresh air return for the reasons you described (definitely do not want a whole second HVAC system for this room either). My water heater is in the garage and furnace is in the attic - any concerns there?

As for fireplace, I'll just have to not have a fire while I'm smoking.

[Nature]

Great info here. I'm really hoping to avoid the fresh air return for the reasons you described (definitely do not want a whole second HVAC system for this room either). My water heater is in the garage and furnace is in the attic - any concerns there?

As for fireplace, I'll just have to not have a fire while I'm smoking.

In that case, I think you would be OK. They would each have their own independent combustion air source and exhaust outside of the living space. You might be OK on the fireplace if it is a direct vent with its own air source to the outside. These would have a sealed glass front and not open to the room.
Keep in mind, I am not a HVAC professional. I wouldn’t want anyone succumbing to carbon monoxide poisoning on my advice.

Make sure to post up what you do. I would love to see it and hear how it goes.