How Condensing Boilers Work – Plumbing Tips

Posted by in Plumber Talk, on October 3, 2017

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A brief video about condensing boilers. How they work. Why they are more efficient compared to conventional boilers. Why they are green and save energy and money. For more information visit our website at

This video is relevant to Oil and Gas.

Hello and welcome to this week’s video. Today I’m gonna tell you all about condensing boilers.
For the purposes of today’s video we’re going to use Grant Vortex Combi condensing boiler. This is the outdoor model as well. All I’m gonna show you in this video is the burner at the bottom, the primary heat exchanger and the secondary, condensing heat exchanger. The first thing you should know when comparing a condensing boiler to a standard conventional boiler is that the heat input is very much the same at the bottom. Roughly 250 to 350 degrees C. This is the burner, we’re just gonna pop out the bottom now. This part here is what inputs the heat at the start of the heating process. This burner here is likely to be fitted with a small nozzle that atomizes the oil, much like putting your finger over the end of a hose. There’s two electrodes that light that oil and that’s what inputs the heat into the combustion chamber and the heat exchanger for transferring heat into the water. Now I’ve got the burner out, we can have a look at the primary heat exchanger. To do this remove this front panel just here. So first we have the primary heat exchanger which is set up in a group of baffles, that all slide out when they need to be cleaned. Burner fan is down in here so hot air, which is heated by the burner at the bottom, goes though these convector fins and tries to keep the heat in this area for as long as possible to allow the hot water to take heat away and off to the radiators. Let’s take a closer look at the primary heat exchanging baffles of this boiler. Right, so here we have the primary baffle area just here. Now remember, most boilers, especially quite old ones, the baffles are really just a metal plate usually just about three of them they’re at a slight angle one, two, three and then that flue gas goes off out to atmosphere never to be gotten back again. Often at about 250 degrees flue temperature.
Have another look at these here, this is only the start of the heat exchanging possibilities. So firstly the hot gases come up through here, round here, up through this small hole here, like so, goes round this part here. Up here, and is again forced round another area. Round here, around the back here, up here, round here, round here and then finally out the front where it then goes up to the condensing chamber. You have two columns like this so straightaway without there even being a condensing part the actual standard primary heat exchanger is already miles more efficient. Because it keeps the heat in there for as long as possible to allow the water a chance to collect heat from that and take it off to the radiators. So, heat comes out of our two little holes at the top goes around, through this condensing area. Each one of these tubes points downwards and has a small, spiral fin that goes down the middle. As it condenses it goes down, causes condensed droplets. taken away in a drain and disposed of safely. So that’s the first major difference between a conventional boiler and a condensing boiler. Most condensing boilers are gonna be more modern and the primary heat exchanging area at the bottom is gonna be better designed nd have much better capability in taking heat away into the water and off to your radiators.
Secondly, we have, obviously the top part is the condensing chamber. How they work that’s different. Most conventional boilers have a flue that comes out the top of the burner and a return that comes in the bottom, because generally the bottom is colder. So, cold water comes back from the heating system in the return, is heated up through the chamber, and then goes out through the flue, back off to the rads. That doesn’t happen with a condensing boiler. The return goes into the
condensing chamber first picking up latent heat from the flue gases. Then it goes in at the bottom of the primary heat exchanger and out.
So effectively you have two heat exchanges instead of one. Right, let’s just slow down for a sec, okay?
We’ll have a quick look firstly of a conventional boiler. So, we have our heat input of 300 degrees at the bottom, our standard baffles, we have our return coming back from the heating system. That water picks up that heat, goes out through the flue 300 degrees starts off around here and we lose about 250 off to atmosphere, out through the flue. A condensing boiler has the same heat input at the bottom has more modern baffles and a condensing chamber on top.

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