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]

Man up I did the virtual orgy in 100 degree temps.

Yes you did! You should be taking notes here for your Herf Shed!

[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.

[josh lucky 13]

Yes you did! You should be taking notes here for your Herf Shed!

I got old barn tin. I plan on tining it up and a smoke stack in the roof with a fan running to exhaust out thru there. I got my plans, that one is just a bit further down.

[WNYTONY]

This is a joke, right ? We talked about this and hell yeah baller - living in the perfect weather why you wanna go inside ????? LOL

Ok, here we go

I'd estimate my room at about 12 x 20 and 8 high. Always just me smoking in here.

Yes, I did an inline fan in the attic above with 2 drops in the ceiling. Fan vents outside thru a window in the attic. I wouldn't recommend just letting it sit in the attic - think you gotta get it outside but I've not tried it. Fan pulls air under the door into the room and keeps anything from going out into the rest of the house. I've never had any problem with it pulling too much air out of the house or anything and I will say it's a little less effective if I crack a window while smoking as it pulls in direct from the window and doesn't seem to clear as fast.
Here's the fan I use
https://www.amazon.com/Fantech-PB370...87&s=hi&sr=1-4


I have a switch that is on a timer so I can set it to run while I'm smoking and leave it running after I'm done, which is usually as I head to bed. Here's the switch I use
https://www.homedepot.com/p/Defiant-...0469/206264395

Lastly, I use a scrubber to clean the air. I have it set on a regular plug in light timer so it comes on several times a day. I think it's for a half hour or an hour at like 5 am, late morning and late afternoon and then it comes on for about an hour and a half at around 1 am which is usually about when I'd dome with my nightly cigar - so it also runs after I go to bed. Here's the one I use
https://www.airpurifiersmoke.com/rev...-air-purifier/

I do get some residual smoke smell as I have some curtains and a carpet remnant under my desk chair but it's not too bad, doesn't get outside the room and is wife approved.

I'm sure you can spend alot more and do a better system, but it works for my situation and it's my home office / man cave so no one but me spends any time in here. Probably wouldn't work for multiple smokers or a room you want to entertain in as common area.

Some of these may not be available any more - I set this up back in 2014 after my kids were gone and not coming back. But these are the items I used - for reference purposes. YMMV

[Emperor Zurg]

I'd concentrate on exhausting thru the existing window if possible rather than poking a bunch of holes in the house. Actually if it were me, I wouldn't smoke in the house at all but I digress... I imagine it's not a sash window tho. That would make things way too easy.

[Regiampiero]

Lastly, I use a scrubber to clean the air. I have it set on a regular plug in light timer so it comes on several times a day. I think it's for a half hour or an hour at like 5 am, late morning and late afternoon and then it comes on for about an hour and a half at around 1 am which is usually about when I'd dome with my nightly cigar - so it also runs after I go to bed.

I do get some residual smoke smell as I have some curtains and a carpet remnant under my desk chair but it's not too bad, doesn't get outside the room and is wife approved.

The reason the curtains and carpet smell is because of the smoke scrubber. That's a particle ionizer which works by charging the smoke particles so they precipitates faster. The pro is that it eliminates the particles out of the air quick, the con is that the particles coming out are charged (like a static balloon) and they stick to the first surface they come in contact with, so floors, furniture, curtains and so on. Hence the lingering smell. The same happens in my garage, but it's a garage and I don't care. I think you have a pretty good setup where you shouldn't even need to run that scrubber, just my two cents.

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[Hermit]

I use a window fan.

[SoCal gunner]

I put a call into an HVAC company to discuss it and hear what they have to say. As many of you so graciously mentioned, I have the ability to smoke outside more so than others. With that said, I'm not willing to go full-bore with a separate dedicated HVAC unit, etc. I'm hoping to go with something like Tony, G, and Mark have talked about. I'm not going to build a full walk-in humidor or any of that stuff either. Just want the option to smoke indoors, if reasonable.