How should I ventilate this?

[Islandkid17]

Hello,

 so I am putting a hot tub in a 25x18 room. The room is kind of like a gazebo as it's just hooked onto my cottage and not heated.  The room is closed in though, but it has lots of windows and I have 4 skylight windows on the ceiling directly over the tub that open. Just wondering if there is anything else I should do to vent the room especially using the tub in the cold winter months. Thinking maybe a ceiling fan or something as well I'm not sure. Want to hear what some of you guys think. 

Thanks. 

[wondertub]

Hi, I was looking into the electrical codes for indoor spas myself, and they seem to restrict placement of things like ceiling fans, while they require a convenience outlet to be placed betwen six and ten feet from it, so a floor fan would probably be easier to put in a safe/effective place. There are ones called air circulators which can be pointed vertically too, I have a "Vornado" like that (660 model), it isn't huge, yet circulates more air than the average ceiling fan I'd say.

[danthespaman316]

Depending how the room is finished (sheet rock, cedar, tile, etc.), I'd really look into installing a large exhaust fan to purge the moist air during usage and minimize the chance of discoloration, deterioration and mold growth to your walls and ceiling. A simple circulation fan will move the air but there's no guarantee that it will find the skylight windows before it condenses, especially considering the overall size of the room. 

[Islandkid17]

Thanks for the replies, the room will be finished. I'll have cedar walls and vinyl floor. Floor and walls will be insulated. I'll look into what was suggested.  Again thank you for the replies. 

[wondertub]

By the way, I was reading a spa manual and it mentions CFM (cubic feet per minute) for ventilating indoor spas. Which should be enough to remove all the air in the room in 3 minutes. Measure the room's length x width x height and divide by 3 to get recommended CFM.  Another reference says we can subtract at least 20 CFM from that for an open window, and I'd imagine more for overhead windows, especially if air flow was directed upward (and hot air already rises by itself). Thermal energy is said to naturally transfer from higher to lower temperature objects or atmospheres, so unless it's blazing hot outside you don't have to rely as much on extra energy to move the air away from a hot tub.  Water is said to be a better conductor of energy than air for that matter, so water in the air could only help.

 

I checked out a small exhaust fan/light I have, and it says 110 CFM (unless it's hooked up to higher voltage), while that air circulator I mentioned says 584 CFM, and a few-hundred CFM is good enough for an average sized room with windows open, or at least I'll try that myself.  I can feel air circulating from across a room with that blowing (in any direction), and it's quieter than the vent fan, which I can't feel circulating anything (unless it were huge—I could feel an industrial one overhead in a hardware store).

 

Reading more about some concepts involved here, fans or air circulators are said to cause forced convection: "If you have a hot object in your hand you could just hold onto it and let it cool by conduction.  That might take a while because air is a poor conductor.  Or you could blow on the hot object and force it to cool more quickly" ... whereas free conduction involves temperature differences in air that make it a better conductor: "because hot air is also low density air, it actually isn't necessary to blow on the hot object, the warm air will rise by itself.  Energy is being transported away from the hot object into the cooler surrounding air. Cooler air moves in to take the place of the rising air and the cycle repeats itself". So between open windows, heat and moisture from the tub, cooler temperature outside, and some air circulation, there are more things working together than in a closed temperature-controlled room, and I don't suppose the CFM would need to be wholly controlled by an extra powerful ventilator, in an unheated open air room (temperature-wise, it would be about the same as being outside to begin with, then ambient temperature differences would cycle air in and out along with moderate ventilation)... and to some extent, the size of the hot tub would factor in there, perhaps how close it was to the walls, more so than whatever was overead to supposedly suck up moisture. I think dehumidifiers are something else, but in a cool open room, a dehumidifier would not do much more than circulate a little air anyway.

http://www.atmo.arizona.edu/students/courselinks/spring13/atmo170a1s1/online_course/week_4/lect11_temperature_conduction_convection_latent_heat.html

[Islandkid17]

On 2017-12-04 at 5:56 PM, wondertub said:

By the way, I was reading a spa manual and it mentions CFM (cubic feet per minute) for ventilating indoor spas. Which should be enough to remove all the air in the room in 3 minutes. Measure the room's length x width x height and divide by 3 to get recommended CFM.  Another reference says we can subtract at least 20 CFM from that for an open window, and I'd imagine more for overhead windows, especially if air flow was directed upward (and hot air already rises by itself). Thermal energy is said to naturally transfer from higher to lower temperature objects or atmospheres, so unless it's blazing hot outside you don't have to rely as much on extra energy to move the air away from a hot tub.  Water is said to be a better conductor of energy than air for that matter, so water in the air could only help.

 

I checked out a small exhaust fan/light I have, and it says 110 CFM (unless it's hooked up to higher voltage), while that air circulator I mentioned says 584 CFM, and a few-hundred CFM is good enough for an average sized room with windows open, or at least I'll try that myself.  I can feel air circulating from across a room with that blowing (in any direction), and it's quieter than the vent fan, which I can't feel circulating anything (unless it were huge—I could feel an industrial one overhead in a hardware store).

 

Reading more about some concepts involved here, fans or air circulators are said to cause forced convection: "If you have a hot object in your hand you could just hold onto it and let it cool by conduction.  That might take a while because air is a poor conductor.  Or you could blow on the hot object and force it to cool more quickly" ... whereas free conduction involves temperature differences in air that make it a better conductor: "because hot air is also low density air, it actually isn't necessary to blow on the hot object, the warm air will rise by itself.  Energy is being transported away from the hot object into the cooler surrounding air. Cooler air moves in to take the place of the rising air and the cycle repeats itself". So between open windows, heat and moisture from the tub, cooler temperature outside, and some air circulation, there are more things working together than in a closed temperature-controlled room, and I don't suppose the CFM would need to be wholly controlled by an extra powerful ventilator, in an unheated open air room (temperature-wise, it would be about the same as being outside to begin with, then ambient temperature differences would cycle air in and out along with moderate ventilation)... and to some extent, the size of the hot tub would factor in there, perhaps how close it was to the walls, more so than whatever was overead to supposedly suck up moisture. I think dehumidifiers are something else, but in a cool open room, a dehumidifier would not do much more than circulate a little air anyway.

http://www.atmo.arizona.edu/students/courselinks/spring13/atmo170a1s1/online_course/week_4/lect11_temperature_conduction_convection_latent_heat.html

Thank you wondertub, this has been incredibly helpful. Exactly what I am looking for.  Thanks again!