When installing a spa inside consider the following points:
The spa needs ventilation similar to a large shower room. The humidity coming off a spa is quite strong. The jets, aeration, and bubble action can create a lot of humidity. This can be dealt with by installing a humidistat controlled vent, sized to do the job and make sure all fixtures, walls, floor, ceiling are made of materials that can withstand moisture.
2/ The floor structure needs to be capable of supporting a live load with the weight of the water and the weight of the occupants. That normally is about 110 Lb. per square foot. This is determined by the weight of the tub, water and people, divided into the square footage of the tub. A small tub say 30 square feet weighing at 1500 LBS of water and normally maximum of three bathers at 200 Lb. ( worst case scenario) = 1700 LB in 30 square feet. 1700 divided by 30 = 56.6 Lb. per square foot. Since it is a live load and considering the affects of age on wood, the engineers normally figure 2x factor on floor structure. That is 113 Lb. per square foot. Please consult your engineer on this.
3/ A good therapy spa, like most of the Haven spas, has great neck and shoulder jets. This means there is spray out. On most jetted bathtubs, there are no neck jets at all, because of this. I would never own a tub without above water neck jets now that I am addicted to the wonderful therapy. Because of this you need some sort of water shield around the tub. This can be accomplished by putting the spa in it's own chamber with a shower type of door.
4/ The air space around the spa needs to be kept from mixing with the whole house heating system. Never allow a cold air return in the spa room. There have been cases where a poorly kept spa emitted bacteria into the air system and made the whole family sick. The headlines read "Hot Tub Make Family Seriously Ill". I have some problems with that. It was the original designer of the installation that caused the problems. If you go into the spa room and the water is sour, you need to turn on the vent right away and dump in about 1/2 pound of chlorine. Then come back later to drain the tub. It would be much better to not let the spa go sour in the first place, but we engineer for the human factor.
5/ Design in a place to keep the spa chemicals up high in the spa room. Use some sort of seal on the door to keep moisture out of the chemicals. It needs to be up high for the sake of little children. Even if there are no children living in the home now, if you sell it there may be some.
6/ If you buy a spa to fit in the spa room, I recommend one with a lip over design, so the spa can be shipped and dropped into the space.
7/ Around the spa it needs a drain to remove water accumulation, from the spray out. For instance if the spa is set flush to a tiled area, that tile area needs to be drained.
8/ Under the spa you need a drain pan, if the spa is on the second floor. The drain should be able to take the volume of about 100 GPM. Plan for the worst case scenario. I had a customer with a 12 -year old spa above the living room. When the pipe popped open, it took out the ceiling, couch, carpeted floor, coffee and end tables. He was lucky there was no one home, sitting on the couch.
9/ Do not use an ozonator inside your
unless it is the 100% SC ozone from Haven Spas. All other ozone
will off gas ozone into the room. When ozone mixes with air it
some poison gasses. Outside there is no problem because it is
10/ The walls of the spa room need to be water
proof against a build up of moisture and mold. Redwood, Cedar, sealed
drywall are all good.
11/ The floor needs to be non-slip
flooring. Do not use any smoothe tile. There are
antimicrobial flooring that keep the spa area safer.
The Freeport spa is used in the above example on size and weight.
The dimensions of the spa are Base frame 55.75 inches wide by 75.25 inches long the corners have a 6 inch 2x frame on 45 degrees to accommodate the radius of the outer acrylic shell. The height from the bottom to the edge of the lip overhang is 27 inches. The spa comes in a framed structure that can be set directly on the floor, or a sub structural floor or concrete, large enough to fit the base of the spa. When the spa is shipped the outer framework has a set of siding boards 1/2 inch thick. These need to be removed before the spa is set in place.
The outer dimensions of the spa are 59x79 to the outer acrylic. See http://www.spaspecialist.com/freeport.html