Friday, August 16, 2013

Interior hot tub rooms


In our new house we are having the hot tub inside the house, should we heat the room?


In a new home depending on where you are putting the hot tub you definitely need to heat the room that it is going in.

Most people when they design a room with a hot tub in it also put in large opening windows or doors so that you get the feeling of being outside but the convenience of having the tub out of the weather. When you do this you need to take special care of how the room is designed and how it is suppose to function.

There is a reason that you have to really think about the way that the room is going to function, a new home is designed so that it is basically a tightly sealed envelope where as little air as possible is allowed to enter the home without being heated or cooled. This means that a hot tub room is the opposite, it is designed so that the air from outside can freely enter the room and exchange the interior air of the room.

With that in mind there are a couple of things that you are going to need to do;

The walls of the hot tub room that are interior walls need to be treated as exterior walls. They should be insulated and have vapour barrier on them just as if they were outside walls themselves.

The ceiling of this room if it has livable space above should get the same treatment as the exterior walls. Preferably it should be insulated with spray foam, actually if you can get away with spray foaming all the walls then you can limit your problems immediately and efficiently.

The room should have a drain in the floor so that any over splash from people entering or exiting the tub or when you are draining the tub the water has somewhere to go. This is a lot safer than trying to attach a long garden hose and running it out a door or window. If the hot tub room is in the basement then you can have your contractor slope the floor near the hot tub to the drain, if the hot tub is on a floor that is on a wood floor then you need to take steps to create a waterproof base. You need that base to stop water from ending up in the floors below or damaging the ceiling.

You need a water supply. Hot tubs require you to add water from time to time, the best way to do that is to add an exterior hose bib, the same ones that you would use to connect your garden hoses. They are frost free so leaving the windows or door open when it’s cold outside shouldn’t hurt it. Having an interior shut-off in the warm part of the house will help make sure there is no freezing of pipes also.

Make sure that your contractor knows the power requirements for the hot tub. Some larger hot tubs require larger wiring to be run to them as the main feed coming from the hydro panel.

If your hot tub is to sit anywhere other than the basement then you should make sure that your contractor knows the size and the amount of water that it can hold. Your contractor needs to make sure that the floor joists are beefed up enough to hold the extra weight.  Hot tubs when full of water weigh thousands of pounds and that doesn’t include the up to 8 fully grown people that can be in them at any one time.

If the hot tub is in the basement, then the basement floor should be at least 4 to 5 inches thick. A lot of concrete floors are poured in new houses at 3 inches. Without any extra rebar installed in the concrete you run the risk of having the concrete crack because of the heavy load the hot tub will place on it.

You should have some heating in the room, this is so that it is more comfortable for you to be in the room before and after you use the hot tub. Heating the room can be tricky. You shouldn’t heat the room with the same furnace that heats the rest of the house. The smell of the hot tub can be drawn back into the house through the ductwork and the opening of doors leading to the room. If you only add heat through ductwork then you end up pressurizing the room, every time you open the door to the room it will allow that air to enter the rest of the house. Most hot tubs need chemicals such as chlorine to keep them clean, that is a smell that you don’t want in the rest of your home. A simple thing to do is to add an exhaust fan, the fan would exhaust air outside, this way the room would always be drawing air to it instead of pushing air out any opened doors.
If you have the ability the best way to heat the room is with in-floor heating. Other alternatives are to use electric heaters installed on the walls of the room.

Make sure that you make the room big enough that you can have seating in the room; this will allow you to towel off or remove your shoes instead of doing it in another part of the house.

If you lower the middle of the room so that the hot tub can sit at a lower level then the floor that you walk in on. This will allow you to enter and exit the tub easier and it also helps with the view as you are at a lower angle giving you more glass and sky to enjoy.

You should plan to have a bathroom next to the hot tub room. This bathroom should have a shower in it so that people are able to wash the chlorine off without tracking it through the entire house.

Proper planning is the only way specialty rooms like an interior hot tub room will function properly. The more thought that you and your contractor put into it the better it will turn out.

Rob Abbott
Operations Manager
Village Builders Inc.


  1. Hi Rob, I enjoyed read this article you posted mainly because we are doing this type of project and I had some questions. We live in SE Nebraska with R-value of 38+. We added onto the back of our garage where our deck use to be the space is approx. 14'x28' we poured a solid concrete floor 6" thick with a drain as you subject since we do have a 2/3 person hot tub spa already that will be going into this space. My question is how much insulation should we place above in the new roof which will be in closed later with seald knotty pine for a rustic look. There will be 80-90% windows on the 2 new walls. He existing walls one is the back of the garage with clap board sidng and the other 28' long is the actual brick of the house. The clap board we wanted to enclose in the treated pine like the ceiling. The hottub will be at the far end it is 5'x7. And the other half of this space will have seating and entertainment system. Any other concerns on insulating and condensation ect. Thank you
    Sheila Westbrook

    1. You should install a humidistat exhaust fan in the area of the hot tub, this will automatically turn on when there is an excessive amount of humidity in the room. Humidity can be really hard on entertainment equipment especially in a well insulated and sealed room. You should also think about installing a couple of ceiling fans to help move the humid air around from off the ceiling and down toward the exhaust fan.

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  4. i need to exhaust a spa room, what type of fan is best,14" duct, with motor on roof, duct in place

    1. It would depend on the size of the spa room. Most spa rooms do not need more the a 6 inch powered humidistat fan to regulate the humidity. But a large room would require it to be sized by an engineer for perfect performance.