Working with a drop-in hot tub is the equivalent of building two pools side-by-side. Once builders start thinking in this manner, drop-in hot tub installation projects become much easier to tackle—especially from a plumbing perspective.
Plumbing a pool system with a drop-in hot tub does not change the original equipment pad design; it only incorporates the addition of two three-way valves. The first valve is installed in front of the pump to control suction from the pool or hot tub, while the second valve is installed after the heater
to divert water to either the pool or the hot tub.
When installing a spill-over hot tub and pool combination, an inline check valve must be installed in the return line going to the hot tub. This check valve will prevent the backflow of water from the hot tub to the pool. Because the spill-over hot tub sits higher than the pool, this backflow will occur when the system is shutdown as pool water is running the waterfall (spill-over).
If the drop-in hot tub has no more than 12 jets, only one pump is typically required. However, if the unit is a spill-over model with 25 jets, for example, a second booster pump should be installed. These pre-plumbed drop-in hot tub shells typically have two, 51 mm (2 in.) suction and return lines. The suction line attached to the skimmer canister in the hot tub must be connected to the suction side of the booster pump. The return water from the booster pump needs to connect to the diverter valve side of the hot tub. This plumbing configuration will allow water from both pumps to be filtered. It also gives maximum water flow with less restriction to the side of the hot tub with the most jets.
The three-port valve is often used when a pool and hot tub share one filter, heater, and pump. In this situation, the water is alternately diverted to the pool or hot tub. Three-port valves are shaped like a ‘Y’ or a ‘T’ and are used in drop-in hot tubs to divert air bubbles and jet water to one side or the other, or a combination of both. The design of three-port valves is such that water flows from one direction and then divided into a choice of two other directions, or vice versa. A handle placed on top of the valve turns the diverter 180 degrees in either direction, directing the flow and mixture of water that passes through the circulation system.
The suction line from the pool enters one arm of the valve body while suction from the hot tub enters the other. The diverter between the two arms determines which line is connected to the stem from which the water continues to the pump. Conversely, when the water leaves the equipment, it passes through another three-port valve. In this case, water passes through the stem and the diverter determines whether it flows to the arm plumbed into the pool return, or the arm into the hot tub return. By setting the diverter equally between the two, water from each side is mixed. When using the spill-over hot tub for sight and sound effects only, the hot tub’s return valve should be set to send the minimum amount of water needed to create the desired spill-over effect. Remember, the pool is designed to self-clean with water movement. If too much water is diverted to the spill-over hot tub, water circulation in the pool may suffer.