This project is located on Tilghman Island in Maryland where inclement weather puts a damper on outdoor soak sessions. That’s why the homeowners opted for a hot tub sheltered from the elements. However, it was important that the spa environment connect to the outdoor living space. “They wanted the wide-open feel, but indoors for year round use,” explains Danny Morris, general manager of AQUA Pools & Spas in Easton, Md. Sliding glass doors give way to a stunning view a 44-foot long geometric pool just off the deck outside. This spa room also includes a shower and a sauna with a unique flooring material that Morris described as “rubberized slate.” It’s a nonslip surface, a wise safety feature.
Danny Morris This project is located on Tilghman Island in Maryland where inclement weather puts a damper on outdoor soak sessions. That’s why the homeowners opted for a hot tub sheltered from the elements. However, it was important that the spa environment connect to the outdoor living space. “They wanted the wide-open feel, but indoors for year round use,” explains Danny Morris, general manager of AQUA Pools & Spas in Easton, Md. Sliding glass doors give way to a stunning view a 44-foot long geometric pool just off the deck outside. This spa room also includes a shower and a sauna with a unique flooring material that Morris described as “rubberized slate.” It’s a nonslip surface, a wise safety feature.

There's nothing quite like the sensation of soaking under the night sky.

But some prefer an indoor hot tub experience, citing privacy as a concern or because they can’t bear the thought of braving the frigid climes before stepping into a steaming tub.

That’s when dealers walk customers through a laundry list of considerations, such as moisture control, access to a drain and the serviceability of the unit, among other details.

Whether their customers plan to retrofit an existing room or build a whole new room around the portable tub, dealers say it’s important to get involved early in the process. That means collaborating with electricians, HVAC contractors and builders to ensure the spa environment will be functional and code compliant.

Here, PSN offers a primer on indoor installations.

Code clears the way
Dealers and service techs report that hot tubs are being installed in master bathrooms, sunrooms and basements with increasing frequency.

The reason for this trend could be attributed to a change in the National Electrical Code that makes it easier to bring these luxuries inside.

It used to be that the NEC did not differentiate between inground and aboveground hot tubs when it mandated that all spas be connected to an equipotential bonding grid to prevent shock hazards. This meant homeowners had to rip apart their floorboards in order to install bonding wires and grids under their portable tubs, even when the units met UL and ANSI/APSP standards. Critics argued that the safety measure was redundant, unnecessary and cost-prohibitive.

So the code was changed in recent years to clarify that a bonding grid was not required for self-contained hot tubs installed above a finished floor. (However, there may be cases when a bonding grid is still recommended. See  sidebar below.) This seems to have broadened installation options.

“It’s getting really popular,” says Torrell Lebron, owner of Crystal Clear Pool and Spa in Culver City, Calif. “You sometimes have whole rooms dedicated to these spas.”

While the code change has made it easier to have a hot tub inside, there’s still the very important matter of determining where to place it.

Location, location, location
When assessing a space to determine if it is appropriate for the hot tub, installers must consider three things: engineering, access and serviceability.

  • Engineering: Will the floor support the weight?


Consider that the typical portable hot tub that seats six to seven people weighs somewhere in the neighborhood of 900 pounds. Add about 420 gallons of water and a person for each seat and you’re looking at an approximate weight of 6,000 pounds, give or take.

If you consider that spa measures approximately 60 square feet, then the floor must be able to support at least 100 pounds per square foot.

Floors in most homes can handle 125 to 300 pounds psf. However, each home is built differently, so diligent dealers should consult with an engineer before determining the tub’s final destination.

“Obviously, part of this procedure would be to know the supporting nature of that floor,” advises Dan Hyatt, owner of Northwest Hot Spring Spas, with two locations in northwest Washington, a region prone to indoor spa retreats. “You’re sticking your neck out if you don’t know and you’re just throwing it in there.”

  • Access: The shorter the distance between a dressing area and the hot tub the better, which is why some opt to have the unit in a master bathroom. It’s a good place to towel off so they don’t walk through the house dripping wet.


While convenient, this placement does have one major drawback: Depending on the model, vibrations from bubbling jets are sometimes felt through the floorboards, potentially disturbing someone’s sleep. Setting the tub on a rubber matt can help. However, these deteriorate over time.

That’s why some dealers recommend a dedicated room far removed from sleeping quarters, such as a sunroom or a greenhouse-type environment.

  • Serviceability: Service technicians would rather not have to army-crawl under the house to access the tub’s interior equipment. Some will even charge extra if they have to contend with cobwebs and creepy-crawlies en route to the spa pack.


But this is what happens when homeowners insist on recessing their hot tubs flush with the floor.

Fortunately, when homeowners want to do that, installers have a couple workarounds. “I had a customer that was going to put a portable spa in his entertaining room and I recommended that we cut the guts out of that thing and reroute the plumbing outside,” Labron says. “That way it’s serviceable and the pumps aren’t there making a bunch of noise.”

Word of caution: Check the manufacturer’s warranty before tampering with the equipment in such a way.

Another option is to create a vault that the spa rests in, large enough that techs have enough elbow room to make repairs.  A hatch makes the equipment accessible through the floor.

“We’re going to oversize a cement vault at least 2 feet on all sides and typically 30 or 36 inches on the equipment-door side,” Hyatt says. “Then we make the composite flooring that we fill in between the floor and the side of the spa removable.”

Swim spas are becoming a popular feature in exercise rooms. This one features an insulated floating cover. Notice how it is partially recessed into the floor.
Northwest Hot Spring Spas Swim spas are becoming a popular feature in exercise rooms. This one features an insulated floating cover. Notice how it is partially recessed into the floor.

Fully recessing the hot tub gives it a custom built-in look. But having a body of water in the floor isn’t the safest way to go. If customers insist on a low-profile tub, a good compromise is a partial recession. Dealers recommend that the self-contained spa be about 13- to 24 inches above floor level so bathers can comfortably sit on the lip of the unit and swivel in.

“The most unsafe thing is to stand all the way up on the deck and step into the spa,” Hyatt cautions.

Keep in mind, also, that the hot tub will need to be drained several times a year.  A floor drain would be ideal, but this would be unlikely if the unit is being placed in an existing room.

“If you’re going to build new, absolutely, you would want a floor drain,” suggests Celeste Pyper, a designer with AQUA Pools & Spas in Easton, Md.

Otherwise, position the tub so that water can be pumped out through a door or window.

Breathe easy
Mold and the potential structural failure of the framework surrounding the tub  are serious issues. But they could be the least of your client’s worries if the room isn’t adequately ventilated. There is also the very real threat of respiratory illness from chloramines.

That’s why dealers should work closely with HVAC contractors who have experience with pool and spa environments.

The Environmental Protection Agency recommends that indoor relative humidity be kept below 60 percent. Inviting a 104-degree body of water into the home will obviously create challenges.

HVAC contractors carefully calculate air and water temperatures and the amount of evaporation coming off the surface to ensure that a dehumidifier has enough capacity to remove excess moisture to maintain a relative humidity of 50- to 60 percent.

The dehumidifier should kick on the moment the cover comes off.

But this is only part of the equation. HVAC contractors aim for a certain number of air changes per hour. This factors in the volume of air being added and removed from a room.

The amount of air being drawn out is what HVAC pros call negative pressure.

“Ideally, we also want to have some amount of exhaust to help create that net negative pressure,” explains Eric Knothe, national sales manager of BPA Air Quality Solutions, a sales and consulting operation in Charleston, S.C. “So instead of pushing humid air into cracks and crevices, we’re drawing air out.”

That negative pressure, by the way, should also reduce chemical odors.

“Your heating and air system and dehumidifier is altering temperature and relative humidity levels,” Knothe says. “But it’s not necessarily evacuating any gaseous contaminates, so that’s another benefit of exhaust.”

Even glass structures housing a spa aren’t immune to moisture damage. Condensation on the glass not only obstructs the view, but a green build-up will develop over time and enough moisture could eventually cause the metal frames to corrode. That’s why Knothe recommends placing a simple standalone unit in glass structures to draw out the moisture.

These professionals suggest using dehumidifiers specifically designed for pool and spa environments, which are built to withstand chemical corrosion.

“You want the coatings and protection inside of it to get the longevity of 8- to 15 years out of the dehumidifier,” Knothe says.

Finally, consider chemicals. While HVAC equipment should reduce, if not eliminate, any chemical fumes, some dealers recommend supplemental disinfection systems as an added safety measure.

Indoor air quality can be compromised by chloramines. To combat this, Labron prefers using ultraviolet light.

“The second I started using the UV systems, I noticed the chlorine demand is lower, and the combined chlorine is almost gone,” Labron says. “And the air quality is a lot better.”

Some spa models come equipped with a UV or ozone system. Those that don’t can be easily retrofitted.


A closer look at the code
Article 680.43 of the National Electrical Code specifies distances of electrical outlets and lights in relation to an indoor tub.

For example, any 125-volt outlet with 30 amperes or less that is located within 6- to 10 feet of the tub’s inside wall must have a ground-fault circuit interrupter. Wall switches cannot be located within 5 horizontal feet from the tub. This is so bathers cannot easily reach out and toggle the lights on or off.

Likewise, lights and ceiling fans located within 5 horizontal feet must be at least 12 feet above the spa where there is no GFCI protection. If they are GFCI-protected, they can be mounted as low as 7 ½ feet.

That’s all pretty straightforward.

However, there appears to be some code confusion around the subject of equipotential bonding. The code was changed in recent years to eliminate the need for a bonding grid for self-contained hot tubs above a finished floor. The key word in that sentence is “above.”

What if the unit is recessed partially or fully in the floor?

According to the letter of the law, hot tubs dropped into the floor still need a bonding grid.
But some dealers feel that equipotential bonding is wise in either case. Just like how pool builders bond all the metal components around the pool, such as the handrail and automatic cover frames, some hot-tub installers take the same precaution when placing a unit inside.

“People may not consider that the same thing would apply if you have aluminum windows in the room or stainless or bronze handrails,” advises Dan Hyatt, owner of Northwest Hot Spring Spas, with locations in Burlington and Ferndale, Wash. “These things should be on a common bonding grid, also.”