Posted by in Plumber Talk, on February 23, 2017

What is the difference between direct and indirect cylinders? We dispel the myths, we cut the cylinders in half and show you the coil, the heat transfer and immersion heaters. If you want to know the difference then this is the video to find out what it is…I hope this video helps you!

If you guys have been lucky enough to stumble across this video, all about indirect and direct hot water cylinders, then great, we’re gonna get down to that any minute now.
What is the difference between an indirect and direct hot water cylinder? Now, if you’re watching this from outside of the UK, this is probably not gonna mean anything to you, but in the United Kingdom, all right, this is a pretty standard way for us to heat up and deliver water to the taps for washing in and all the rest of it. So, I’m gonna have two tanks appear either side of me right now just like this. On this side, we’re gonna have our indirect tank, and on this side, we’re gonna have our direct tank. So, the differences are, and let’s firstly look at the indirect tank.
The indirect tank next to me here has usually an immersion heater in the top or the bottom, or if it’s an Economy one or if they’ve got some sort of photovoltaic solar panel system set up, they might have two. You might have a top one and a bottom one, but for the indirect hot water cylinders, that doesn’t matter. The main heat source comes from heated water from the boiler. Now, that heated water comes up. It usually goes through a two port or a three port valve, which is gonna direct hot water through a coil inside that hot water cylinder. Now, that is the main thing that differentiates it from a direct cylinder. The water comes up from the boiler through our control valve according to the thermostat and the time clock that’s on that system, and then it goes through that coil and the water, the two bodies of water, don’t mix at all. You’ve got the hot water from your boiler, which if it hasn’t been inhibited properly is gonna be all black and manky, and also, let’s face it, even if it has, no one wants to be washing in the water that comes out of a radiator, all right? So, that water is kept inside that coil nice and hot, usually gets introduced at sort of degrees, maybe degrees, which is the boiler temperature coming out and then it transfers its heat into the hot water, okay, that you’re gonna be washing in and the water that comes out of the tap, and then usually on the side of an indirect tank, you’ve got a little thermostat, and that usually gets set at roughly degrees. So when it gets up to degrees, it signals to the control valve to shut off the flow of hot water to the hot water coil going through the tank, and also it tells the boiler and the pump to go off. And that is what an indirect hot water tank does. It effectively has two sources of heat, the direct source, which is what you’d say was the immersion heaters that are in it, and the indirect source, which is what you’d say is the boiler somewhere else in the house which is putting hot water and is being circulated through a coil in the tank just like that. I mean, if we look inside this absolutely naked indirect tank here, you’ll clearly see the coil inside the tank there that has hot water flowing from the heating system in the boiler going through it and then back out the tank again, transferring its heat into the water that you’re going to wash in. If we look at the direct tank to this side, it’s so much more simpler. There is no coil. You don’t have a coil coming from the boiler. There’s nothing like that. All you have is usually an immersion heater at the bottom and sometimes an immersion heater at the top as well. This is especially common on Economy systems and Economy systems. The difference between the and the is purely how much of a cheap rate you have in electricity, the idea being is the top immersion heater is a boost immersion heater, so say you get back, I don’t know, : on a Saturday morning, and you’re at a high rate of electricity, but you still want a bath. You press that boost and all it’s gonna try and do is effectively kind of heat the top part of the cylinder up, but then at night when you’ve got a lower rate of electricity, you have what’s called a night setback immersion, which is the bottom one, and what that does is that comes on when the electricity rate is nice and low, and it heats the whole tank up just like that. So, you’d say that because you’ve got those two immersion heaters in there like that, that it’s a direct source there and then, and that’s it, it’s a direct cylinder.

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