15 Feb 2015

Residential Indoor Pool Humidity Control & MigrationTreatise

Growing trends in the HVAC Industry and new construction building. No Comments

                      Residential Indoor Pool Humidity Control

Indoor Pool Humidity Control




This article is meant to be an exercise in idea’s concerning a house that contains an indoor swimming pool separated by a wall from the rest of the house. We are going to assume the house is built correctly with all the proper vapor barriers in place. Using materials that will not be destroyed by humidity.There will be a modern H.V.A.C. system in place and a proper Humidity and temperature control system for the pool. The pool water will be heated to 75 degree’s F the air temperature will be close to that and our goal is to maintain humidity in the pool area at 50 to 60 %. We are in a region of the country that has all four seasons and the winters can be very cold and last quite a while.

Residential Indoor Pool Humidity Control & Migration


The question here is really about migration, humidity control is pretty straight forward. Not to say it is easy, it is not. It needs to be done correctly. But the right sized system with all the proper duct work should take care of it nicely.

The real question is our case is How do you control migration of the humidity between the pool and the main structure?

The answer we get from experts is to use pressure differential.

If the structure is built very tight then the way most experts address this problem is by cutting a hole in the building envelope and installing a fan that is pulling from the inside and discharging outside. By doing this they are pulling a very slight negative pressure on the pool area creating a pressure difference between the pool area and the rest of the structure. Thus in theory stopping the migration of excess humidity into the rest of the home.

The rest of the home having a slightly higher pressure would be protected and would be the one loosing it’s conditioned air to the pool. I will ad a hand drawn picture of this. I believe in our area of the country this may be the least expensive to install but over time is not good solution. At a minimum large heat recovery ventilators should be used in place of just a fan. Think of all the energy lost using this method. The infiltration factor for the room has to increase. Every flaw in workmanship will now become a place for infiltration.


Below is a letter I wrote to a customer concerning this very theory and I will ad to it after the letter. This customer also had a large organ in the house that required humidity to operate as per the manufactures recommendations.


 To whom it may concern:

I just wanted to talk to you a little about know facts and some theory. The first fact I want to mention is,  your organ company wants you to maintain a certain amount of humidity in the air all year round, 50 to 60%. Doctors say humidity in the air is good for us. Humidity is not bad, as long as it is not in excess of 60%. And as long as the only source is not your pool water evaporating.

So if your pool dehumidification system is doing it’s job we should have about 50% humidity in the air.

So a little migration from the pool to the house considering you have this new salt water system isn’t really all that bad. So stopping it is not as important as minimizing it to a degree. If there is 50% humidity in the pool, and also 50% humidity in the house, there is no place for the humidity to go. It just stays where it is.

In a structure designed to hold an indoor pool. Pure exhaust in order to pull a negative pressure on the pool area seems like a big waste of money. To me that is why I didn’t bring it up. However I can install it if you like. They had that system installed in a YMCA I took care of and I believe it has flaws. Whenever a negative pressure exists in a space that is not 100 % sealed there is always a higher pressure waiting to get in. This is a fact. That higher pressure is the outdoor air or the conditioned air from your house. So in the winter when energy is at its highest (unless you are using recovery ventilators) you are expelling energy from the pool area and replacing it with energy from the house.

This would all be different if the pool was in a standalone structure of course but it is not. Why worry every time you open a door that you are releasing this pressure. You want to enjoy this lovely pool. I say keep the pressure the same, save the energy that going to be expelled from the house and use it to humidify if necessary so all things being equal there won’t be any migration.

Experts who are in the installation field not the theory field will say that maintaining 60% humidity in the pool is unlikely. The real number will more likely be 50%. This is a perfect % of humidity in the house to maintain people health as well as the health of the organ. All the energy used to make humidity will be used in the house and not simply expelled. And with the use of ERV units as much as 70% of exhausted energy and humidity can be captured and put back into the structure. We can take all the condensed water we have from the house and pump it into a cheap plastic barrel in the mechanical room and you can even use that water to water the indoor plants. No waste!!!!!!!

In another letter I went on to explain the H.V.A.C. system in the house will need to be set up with humidity sensors built into the thermostats and that in the winter we would need to humidify the house and in the summer dehumidify. The entire time maintaining what ever humidity level we have agreed upon. By doing this the migration would be minimal. You will be able to open and close the doors to the pool with out much worry. You would almost certainly reduce the pool water evaporation by eliminating the negative pressure fan.

Greg Murphy



Let’s talk about this more. There is no doubt what I subject will cost more then a fan pulling a negative pressure. That should not be the main consideration. Even a small indoor pool done correctly can cost $500,000 or more to add to the project. I’ll bet the one in the little picture above was more like $750,000. The main house is 3 times that much. Out of all the things on the project why try and cut corners on the mechanical s concerning the pool and the house. You will pay for this in the long run! This is a guarantee!

I witnessed an indoor pool installed years back in which the area around the pool was filled in with out the pool itself being surrounded by insulation. I don’t know how much was saved but I’m sure by now they have spent ten times that amount on energy. Helping to heat the northeast region of our country.


I would like also to help a bit with anyone considering floor mounted dehumidifiers. The only way I can see this working is if you have a indoor structure made our of concrete with no windows. With no worries of condensation.


  Dehumidification is not just about lowering the humidity level. There are a lot of factors involved. All windows and doors and some exterior walls should have a blanket of air on them at all times in order to prevent or minimize condensation. This may mean underground ducts, ducts built into the walls plus overhead ducts and branches pointing into skylights.


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