Hey there, this is a short episode of the HVAC school podcast, just a small little nugget that, hopefully, will be worth your time and before beginning into that, I want to thank our sponsors, one of the people I want to thank that, isn't technically a sponsor, but It's a company that we work with a solder weld. If you haven't taken a look at solder weld products, then I don't know where you been, but you can go to products by pros.com and you can find out more about solder, weld and where you can buy it locally or if you find that you can't buy It locally, then, you can go to true tech tools and specifically, I'm gon na suggest that you look at the all-in-one kit by solder, weld, I think, you're gon na, like it it's a very good value for what you get comes with everything you need to. Basically do all of the brazing and soldering jobs that we run into an HVAC and appropriate quantities, and then I also want to thank filled. Peace filled, peace, comm, refrigeration, technologies, makers of all sorts of really good cleaners and products.

Chemicals for the HVAC industry that are more natural and less chemical navikev. A global comm makes all kinds of great tools for the HVAC industry, they're innovating a lot of new products into the US market that you may be interested in, and you can find out more about them at true tech tools as well. If you want to see the price points on some of the products and again that code gets cooled, always works for these products today, one time a stack effect, stack effect, stack effect gets a real wrap and I think there's some confusion about stack effect. So, let's address it, the idea is that hot air rises, right and hot air does rise, but a better way of saying it.

I think, at least from my mind, is hot air floats on top of cooler air, so he doesn't rise by itself. He'd actually just causes molecules to vibrate more quickly or move more quickly. So when you increase the temperature of something you increase, the average molecular velocity. That's what temperature is.

Temperatures average molecular velocity. So when something is a higher temperature, it means that there's more speed of the molecules that molecules are moving faster. My definition, then something that is a lower temperature. So that's really what we're measuring so when you have air or the molecules are moving faster than those molecules separate from each other if they're allowed to and that results in air that is less dense.

So when something is less dense than something else, the less dense thing is going to tend to float on top of the more dense thing. And so that's what we see when you have a rubber ball, that you shove down into a bathtub and you let go of it. It floats up to the top, because the air inside the ball, the overall density of the ball, is less than the density of the water around, so it floats, it's density is less lower than that's how we can think of that and when you think of air, The air that we work with most often isn't pressurized we're not pressurizing air in a building, at least not to any large degree. Obviously water column scale.

We can measure pressurization of the Pascal scale. We can measure it a little bit but we're not like packing air into a room. That's not our intent like we are in the case of refrigerant, where, when we pressurize something, we know that the temperature increases and we depressurize it decreases, and mostly what we're doing when we change the temperature of air. One of the big facts is that you change the density of the air, so when you heat it the molecules they move more quickly, and so they bounce against each other, and they tend to separate to say that heat rises is kind of false, because hot stuff Tends to rise within itself, so if you have hot air and cold air, then the hot air rises or floats above the cold air and the cold air sinks, colder air sinks, lower temperature, air, that's what we say, colder colder just means lower temperature than something else, And so when we say warm air or hot air rises, what we're saying isn't that hot air intrinsically always Rises? The point is, is that when you have air that is of a higher temperature than the air around it, then it floats on top of the colder air or you could just as easily say the colder air sinks below the hot air.

But those two things happen simultaneously, and so we say this thing that hot air rises, and so, if you think about a house that is a furnace in it and we dump all this heated air into it, we're running it from the house through the furnace. The furnace heats the air and then it puts it back into the space, so it's actually increasing the volume. So if you measure the volume of air that goes into a furnace and the volume of air that comes out of a furnace, if you measure it perfectly, the volume of air will be greater coming out of the furnace, because, by increasing the volume you've decreased. The density as there is less dense coming out at the top of that furnace so that hotter air hotter than the air in the room is going to tend to float on top and the colder air is going to sink below.

So what happens is is if you have a two-story house or house with high ceilings, and you dump some hot air into it out of a furnace, then that air is going to lift and naturally, as that lifts. What's going to tend to happen is that it's gon na leave a vacuum in behind and it's gon na draw in colder air, so you're gon na end up with colder air on the floor, that's drawn in from under the doors and around the windows and any Cracks in the walls low in the building it's gon na draw in cold air and then that warmer air is going to lift to the top of the building. It's almost kind of like a balloon, but the things not taking off you just have this balloon of air, this body of hot air, that's rising to the top. Just because the density is lower within in cooling season.

We get reversed stack effect. So that's we call stack effect as hot air rises to the top, and that happens when you're heating, the air, through an appliance to the air that's coming out of the appliance, is warmer than the air, that's in the space. So when we do the opposite, when we cool the air so we're putting cooler air and then the air that's in the space, then that cooler, air sinks and the warmer air displaces it and moves upwards. So what happens as that cooler? Air sinks is, as there's that motion that movement away then what happens is is it creates a negative pressure in behind, and so we get reversed stack effect.

So that's where we tend to draw in hot air, from around open, can lights or around ceiling boots or around any gaps and cracks or not the top of the drywall. So, in places like Florida, we're very concerned about ceiling around the ceilings, because we're primarily cooling so as we put that cold air and it sinks down, and it creates a negative pressure at the ceiling which drags in that nasty air from the Attic, whereas in colder Climates where you're running the heat, more often you get the stack effect where it's drawing in from the floors, and that's where things like door sweeps become very, very important and you'll notice. You're running the heat, you have a gap underneath the door that cold air is just rushing in or, I should say, colder. Air, lower temperature air is rushing in to take up the space and it can be helpful to think about that, and so it's more important when you're heating to make sure that the low areas are sealed in order to prevent that cold air.

From coming in due to the snack effect and then in cooling season, it's more important that we seal the upper parts that we were not drawing in hot air, but either way that stack effect does occur. And there's these pressure imbalances, because that air is moving. But instead of thinking of it is rising, I think it's helpful to me to think of it as simultaneously floating and/or sinking, so cold air sinks. Hot air floats just in the same way that things sink and float in water.

For my brain that helps me kind of imagine it a little bit better so hopefully that it helps you, and we will talk to you next time on the HVAC school podcast.