How Condensing Boilers Work – Plumbing Tips

How Condensing Boilers Work – Plumbing Tips

– [Announcer]
Honest reviews and advice. Sponsored by – 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. The condense itself is
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 and 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. This time the return
comes back from the system into the connecting chamber first and picks up latent heat. Now, the reason it condenses is, if you imagine you breathing
on a window on a cold day it will condense onto that window. So, as cold water comes back
into this really hot area it will condense through here and a little condense
drain will take that off and safely dispose of it. After going through
this condensing chamber return flows down into the
bottom of our primary chamber takes up this heat here and
then goes off back to the system This time, our flue temperature
will be about 55 degrees C. So that shows that you
have the same heat input at the bottom as a conventional boiler but you save all this energy
because so much extra heat is being extracted and put into the water that goes off into the radiators. Remember, there are
two much more efficient heat exchanges here. Even when the boiler is not condensing because sometimes when the
return temperature is warm it won’t condense it will
always be a lot more efficient. I hope you found today’s
video interesting and helpful. If you think we haven’t covered anything or you think we should have
done something slightly better please do contact us on our YouTube. And as ever, don’t forget to subscribe. See you soon everyone, have a great time. Bye. – [Announcer]
Honest reviews and advice. Sponsored by

89 thoughts on “How Condensing Boilers Work – Plumbing Tips

  1. Another good one mate, you explained the boiler very well.
    Pity about the dodgy boiler install though!! Who on earth ran that 21.5mm condensate pipe & will it survive another Winter without freezing up?
    Better hair cut by the way, at least you don't look like you've been dragged through a hedge backwards…………….Keep them coming, thanks mate…….;-)

  2. Great video. Is the condensing boiler service procedure much different from servicing the conventional type? I know the burners are the same.

  3. You do great some great plumbing videos, at least I don't look too stupid when calling out someone to fix my heating system. I shall be subscribing to your channel.

  4. Nice video with great explanations etc. I would just add to it a little and explain to the non technical people watching that the energy and money saving advantage of this boiler comes from the fact that the boiler needs to work less to get the water up to flow temperature. Hence the efficiency level being greater than a normal boiler. The key element is get one because it saves lots of oil (therefore money) when heating your home and water.

  5. hello how are u my friend? i need some advice from you about my boiler which is green star 25si/30si bolier (worcester) the problem is with the pressure gauge which is on 0, when i tried filling the system the gauge stays on 0 and dont fill up. it would be great help for some feedback. thanks

  6. I need a new oil boiler. i have a Velaime Vitesse in at the moment on a reguler system. which boiler would be best to replace it?

  7. Big dude. I've got an old gravity fed boiler, with HW cylinder and F&E tank. It's making a 'shit' load of noise. There's loads of Inhib and boiler descaler in that mother. Can I 'razz' out the heat exchanger and 'slap' that 'mother' in a bucket of descaller? Rads also need bleedin' bleeding a lot, is that from the boiler 'descalling'?

  8. OK dude, I don't understand what I say either, must be the ginger beard. I've drained and flushed, water was yellow and F&E tank was full 'o' gunge. Not all that old, 6 months. Refilled and added 2x inhib and descaler, sounds better, It's almost like a kettling sound but not that bad. Wondered if heat exchanger was scaled, out water is pretty hard.

  9. Just want to say, I'm a third year mechanical engineering student looking into a project to optimise condensing boiler efficiency. I had experience with heat exchangers but no experience specifically with boiler. Your video and the images contained within it were very helpful to help explain and understand condensing boilers very quickly. Cheers

  10. why lol 🙂 is it because we might go out to the shed and pull our own burner apart and end up burning the shed to the ground or sumthin haha

  11. That was a fantastic video. I presume that condensing gas boilers work the same as the oil boilers? Can you recommend a brand in the USA? I was looking at Weil-Mclean vs. Buderus vs. Triangle Tube. Which is the best for a 3,300 Sq. / Ft house?

  12. Very good video.. I have one quistion tho. I ordered a gas boiler for a job, but the delivery guys said that a gas boiler would not do the job, due to the temperatur on the water comming back to the boiler only is 4-5 degree lower than the water comming out. He says that i wornt condensate, and therefore cant work, without beeing able to explain why. But as you say, dosent that just lower the effency of the boiler?

  13. You might consider studying a faster feed of the water going through the condenser section (impeller then reduction) just to pick up as much heat as possible. (Rather then just trying to make the current set up more efficient)

  14. I've got the same condenser boiler but the hot water output (immediately after the pump) is connected to the cold water return through some sort of pressure valve… any idea why this might be? I seems a rather bizarre thing to do

  15. Very good explanation mate. All other condensing boilers that I saw until today were gas fired, instead of oil fired.


  16. Great video, very informative!!
    Just wondering, has anybody in the UK tried Hassle Free Boilers yet? I heard they do new Worcester boilers with no upfront cost and no deposit.

  17. Pretty great explanation, although a little more elaboration on exactly what the condensate is would have helped me!
    As I understand it, condensate is the corrosive material extracted from the return water? Not sure if this is correct, but I'm wondering if it is, and also what form the condensate is in? Is it also a liquid? I'm confused about the difference between the condensate leaving the condenser, and the return water leaving the condenser…

  18. Great video but can you explain a little about how the modulating valve and the venturi system works on a gas boiler and how the gas flow rate is regulated.


  19. Thanks for very interesting video. Also, thanks for NOT putting bad background music on like some other Youtubers seem to do.

  20. i study all youtube videos every day and i love learning from them but i have to say i rate you,r videos for plumbing as the best on youtube from a 68year old pensioner

  21. most people dont need condensing boilers, because their edr is very low or they use water based radiator. Only if you have steam based radiator.
    i see alot of people get oversized boilers, the only reason last long for old models is they have good thermal mass, and cast iron radiators especially, keep giving heat even after boiler shuts off and short cycles to death.

  22. Nice vid but I wish sales people and some plummers would educate customers on the correct application of these boilers before selling them as a replacement to older boilers. The increased efficiency is only realised if the return temperature to the condensing boiler is kept below approximately 55°C. Perfect for low temperature applications such as radiant floors and low temp radiators, but not much good on rads whose sizing was based on the old ΔT60 test standard. Take my advice, if your putting a CB into an old home with existing rads, install a weather compensator to get some benifit from the new CB

  23. You really are a very helpful chap. Very knowledgeable . I have a condenser boiler. I'm going to watch this again for more help. Thanks!

  24. Great vid thanks, i am looking to buy a new energy efficient condensing boiler and was wondering why they all seem to have plastic flue outlets, but if the heat is reduced to around 55 degrees C that would explain it.

  25. Great vid, I have just had a new vortex combi similar to this one installed and am really impressed at how efficient it is, thanks for explaining why.

  26. Thanks for all your help pal, really helpful videos!!! Would just like to ask, is there a common fault that occurs with condensing boilers after you have filled a system back up once you have finished working on it? Recently helped my wifes old Grandad out with a leaking rad valve replacement but now i think i have broke his condensing boiler lol it's a gravity fed system which is connected to a condensing boiler, please help?

  27. I have been reading my uni books to revise these bits, 6 minute video with your explanation and I get it straight away. Thanks, really appreciate it! 🙂 Excellent tutorial!

  28. Thanks for posting up this informative video and in layman's terms. That is amazing that a normal boiler outputs 250c at the flue , but the new condenser boilers only has 50c lost out of the flue!, that is a hell of a saving of oil I bet and less carbon/heat lost into the air!
    Can I ask a question if that is OK please. You know the manufacturers say that the condenser boilers run the most efficient in condensing mode and it only runs in condensing mode when the temperature is less than 55 degrees centigrade, do they mean the temperature coming out of the flue of the boiler or the temperature coming back on the return water pipe to the boiler coming back from the radiators?

  29. Beautiful, so its the same concept as an economizer in an industrial size boiler application. Uses "Leftover" heat to preheat the return water.

  30. So it's nothing to do with any sort of special burner after all?Just a very logical combination of plumbing and flue gasses. Great video!

  31. Modern technology is a bonus on condensing boilers, on the negative side you will go through 3 boilers compared to 1 cast iron mexico due to acidic corrosion inside these exchangers.

  32. Hello! It was hard to understand but your video did the job!
    One thing i dont get though!
    Why is it not as efficient when not condensing? In my understanding, return water, even if hotter, still passes through secondary heat exchanger and picks up heat.
    It is not hotter than flue gasses is it? I cannot find any info on this anywhere!

  33. Hii mate,

    i am not sure i am getting things right with on demand boiler then the older heat oil type of boiler which is not on demand type.
    anyway, i am so confused about the types of boilers available.
    can you do a video on type of boiler for house hold ? and configuration of each ?

    i am trying to understand my aunties boiler system , which they obviously know nothing about..

    one of my aunt in uk have a heating oil type of burner (i know it is pressurized because it has a pressurize membrane vessel),
    and there are so many piping running here and there (they have 3 zoning and each have a pump of itself) , and also a heat storage container, which have also electric heat installed (it is a dual heat).


    another aunt have gas on demand heater for radiator and shower in germany which have a (i think) over 50 gallons of hot water stored in the vessel beside it. and there are several pipes goes in and out of the vessel (which confuses me). i know the heat exchange surely happened inside the vessel itself, but i have no idea which pipe is the closed loop hot water of the boiler system, and which is cold water inlet and stuff..

    both of them i am trying to learn how the piping goes.. since some part of the piping hides inside the walls.. i can't really get the picture where they goes.

    can you pls do a video on such theme in complete ?

    it will be very appreciate. then i will be able to troubleshoot in case anything happen


  34. I live in the states don’t have a lot of condensing boilers here. In Maine it get pretty cold how do they work at 0 degrees f. For a month straight do they run on kerosine or Home heating fuel. Is it worth the price to switch over from a Buderus g115 to a condensing boiler?

  35. hey, thanks for sharing this info as an experienced service engineer in one of the best Combi boiler company I have seen most of the people don't know how to maintain properly that is the only reason for all the problems if they maintain with frequent cheaks no issues will raise the way your explaining is good keep going

  36. Links to the tools I use everyday here:

    Plus, follow my Vlog “TimesWithJames”:

  37. If that boiler was mounted on a slab suspended on a plinth hard against house and condensate was discharged through hole in lbottom of boiler casing and slab to drip onto soil 300mm from building, do you think this will cause problems with founds?

  38. hi, is it the water entering the secondary heat exchanger that's condensing or the flue gas across the surface of the secondary heat exchanger that's condensing? thanks.

  39. Hi.i had my old boiler replaced with a glowworm 25c combi about a year ago.
    It heats 8 small to large rads on 3 floors in a small 200 year old building which ive insulated well.
    I dont know if it is a condensing boiler. I dont know what central heating temp to set it to on the boiler.
    The info about temp setting for central heating and hot water is missing in the manual.
    It has been running on almost max temp since it was installed,but
    I learnt myself that i should be running it cooler to start it condensing and performing properly.
    The max central heating temp is around 75 c ,so i have turned it down to 50 c,to get a cooler return flow of 40 c maybe but i have no way of measuring this.
    Will this manual lowering of the central heating temp (by me pressing a digital button on the front) make a difference or do any internal master settings have to be lowered by the installers/qualified engineer.
    There is little info from glowworm.
    I read i might need to fit an outside weather thermometer thing.
    I had a hive remote thermostat fitted but thats just a glorified temp adjuster is doesnt seem to teach my boiler to perform better like what ive read about the outdoor weather thermostat things.
    Any help greatly appreciated thanks clive

  40. So a old conventonal boiler running for 1 hour uses the same amount of oil as condenser boiler. only the condenser captures more of the lost heat enery lost out the flue.the only way of really saving money is to have your house better insulated to hold this extra waste heat and to be able to run your boiler less.

  41. So its effectively using the exhaust to heat a secondary heat exchanger to preheat returning input making it easier to heat up fully when it goes through the main heat exchanger with the overall thing retaining most of its heat rather than pissing 250c out of the exhaust which could have been utilised?
    What about adding a second condenser to further draw latent heat from exhaust gases or is there really no point?

  42. Hey I know you posted this like almost a decade ago, but just as several of other viewers I too wanted to say, it was a very good educational video. really helped me with my studies understand condensing boilers and the mechanisms that make them more efficient.

  43. Hi there interested stuff. here I would like to know a bit more about the condensing process. My understanding is that water vapour in hot flue gas will condense an change state from gas to liquid when touching cold surface of the return pipe. This will cause water vapour to give off latent heat to fluids (e.g water ) in the return pipe through conduction heat transfer. please correct me if any of it wrong. thanks

  44. Hi mate. Im getting a lot of condensate out of the white outlet pipe. the prv valve also has limescale around. It. And I’m daily refilling the filler loop as I lose pressure. Any tips please?

  45. would i be able to replace m y old kaput Worcester combi oil boiler that has 5 connections to it,
    heating flow & return, domestic flow & return, & mains water supply pipe.thanks regards.

Leave a Reply

Your email address will not be published. Required fields are marked *