Our kit-built sunroom has room for a 2-person above-ground hot tub. Electricity and water are available in the adjoining kitchen wall. There's cement flooring. The sunroom door would provide venting. Drainage and soundproofing the pump are the only problems I see. What costs besides the tub might we have?
Hi, I haven't seen too many hot tubs installed inside a sunroom--actually I don't think I have ever seen one--and I would be a little concerned about the moisture it would generate. Hot tubs can get pretty hot and that results in a lot of humidity in the surrounding area. When they are on a deck or patio that humidity just escapes into the atmosphere, but in your sunroom there isn't anywhere for it to escape to. I assume your sunroom kit consists of a room with a lot of windows and a door to the exterior and to the interior of your home. Keeping the exterior door open as you suggested would provide some ventilation--provided it's screened to keep the bugs out--and Colorado's dry air would also help, but I think you are going to need some sort of ventilation system to circulate the air.
A lot of the moisture from the tub is going to collect on the inside of your sunroom and eventually cause some expensive damage. I have built indoor pools in the past and while a hot tub is on a smaller scale, the water is also much hotter. I had to put in pretty elaborate ventilation systems to keep the humidity level down and while I don't think you'll need anything of that level--I think you do need something. I suggest you have a contractor around Colorado Springs take a look at your situation and give you some suggestions. They may be able to visit the job site and see something I'm not aware of and it turns out you don't need any additional ventilation.
As far as the other costs, it sounds like they should be minimal. Your concrete slab should be able to support the weight of the hot tub without a problem and you can fill and drain the tub with garden hoses. The electrical hookup might be a little more complicated than you anticipate. A hot tub should be on a Ground Fault circuit and there should be a disconnect located close to the tub. Depending on the location of your panel box, I would estimate that it could cost $300-$500 for your electrical. It might be a little less with the hot tub not being located outside and if your panel box is in close proximity. I'm not sure on labor rates in Colorado Springs either so that could cause it to vary a little.
Wiring a hot tub is not a job for a DIYer. Use a licensed electrical contractor and get the work inspected by the local building or electrical inspector. Electricity and water can be a dangerous combination and someone who knows what they're doing should be involved.
I'm not sure how much sound proofing you'll need for the pump. Most of the hot tubs I've been around are fairly quiet.