New to forum - ex plumber (with a question!)

[Ric2013]

Chris X.

If I were burning with a 78% efficiency, then I would only get 78% of my 130l, which is 101l. I think a Profile is SAP rated at precisely 78% actually!

No offence taken at all. I see where you are coming from. I just would like to get my consumption down further still without turning the heating off altogether, but I think you've got what I mean now...

Obviously I accept that heating my water is not my biggest environmental impact, but it is something I would enjoy getting as efficient as possible, without replacing the boiler, because, as Dave has made me see, the lifespan of new boilers and embodied energy could well make a new boiler a false friend in this respect.

Going back to the water heating question, if we accept 78% as the boiler efficiency (ignoring the fact that it is cycling through much of the water heating stage), I'm probably only using 20 or 30 litres of hot water a day (I'll measure this tomorrow).

If so then, would it be fair to say that the boiler is heating 25 litres of DHW to replace that I have used, but the system is losing 85 litres of water heat through the cylinder walls and through the primary circuit from boiler to cylinder? Because, if so, I am running at an overall efficiency of 19% and electricity would actually be a more efficient way of keeping my cylinder hot, (which is ridiculous)?

Is your home detached?

I think the OP's happy for us to continue off-topic. FWIW, I pay a little over 16p per unit of electricity and this hasn't changed much at all in the last 5 years. I'm with Ebico.

 

[CHRISX]

Chris X.

If I were burning with a 78% efficiency, then I would only get 78% of my 130l, which is 101l. I think a Profile is SAP rated at precisely 78% actually!

No offence taken at all. I see where you are coming from. I just would like to get my consumption down further still without turning the heating off altogether, but I think you've got what I mean now...

Obviously I accept that heating my water is not my biggest environmental impact, but it is something I would enjoy getting as efficient as possible, without replacing the boiler, because, as Dave has made me see, the lifespan of new boilers and embodied energy could well make a new boiler a false friend in this respect.

Going back to the water heating question, if we accept 78% as the boiler efficiency (ignoring the fact that it is cycling through much of the water heating stage), I'm probably only using 20 or 30 litres of hot water a day (I'll measure this tomorrow).

If so then, would it be fair to say that the boiler is heating 25 litres of DHW to replace that I have used, but the system is losing 85 litres of water heat through the cylinder walls and through the primary circuit from boiler to cylinder? Because, if so, I am running at an overall efficiency of 19% and electricity would actually be a more efficient way of keeping my cylinder hot, (which is ridiculous)?

Is your home detached?

I think the OP's happy for us to continue off-topic. FWIW, I pay a little over 16p per unit of electricity and this hasn't changed much at all in the last 5 years. I'm with Ebico.

Hello again Ric2013,

I don`t know whether You have lived in your Home since the Boiler was installed regarding whether you have had control over whether the Heating system has always had Corrosion Inhibitor in it ?

The reason why I mention that is because what you have described about the Boiler seeming to be using MUCH more Gas to heat your Hot Water Cylinder than should be required sounds like a situation where the Boiler Heat Exchanger has a lot of Limescale that has to be `heated through` before the Water flowing through is heated.

Having asked You about the Inhibitor even if there has been Corrosion Inhibitor in the Heating system throughout the last 30 Years there could still be serious Limescale build up in the Boiler Heat Exchanger because as the term `Inhibitor` states it is NOT a Corrosion / Limescale Preventor.

IF this is the case with your Boiler when You are using your Heating system the situation regarding the excessive Gas usage compared to the Heat produced would be even more apparent - which makes me wonder about your previous comments about the Temperature settings that you have been using etc.

If the Cylinder and primary circuit pipework were causing the BIG discrepancy that you described in the amount of heat being produced by the Boiler compared to what should be required to bring the Cylinder water back up to the set temperature there would have to be a massive Heat loss happening somewhere - BUT I know that You will at least have a properly insulated Cylinder even if the primary circuit pipework is not insulated.

Even if You have quite a long run of uninsulated primary pipework I cannot see how that could cause the loss of Heat to the Cylinder that you have described.

Please don`t take this as me trying to be `funny` in any way - You mention only using 25 - 30 Litres of Hot Water per day but what about Showering or a Bath - even an average gravity Shower must use about that amount of Hot Water for a 10 minute shower ?

Regarding using a 3Kw Immersion Heater / Electricity to heat the Cylinder when I have done this in the past while I was doing work on my Home which included installing a new Boiler it was taking 2 Hours [36" Immersion] to heat about 66% of the Cylinder [Immersion not reaching the lower third] - if this was at my current Electricity price of 16.24p per KwHr it would cost 97.44p.

However if the Immersion Heater was then left on to keep the water hot throughout the day that would become prohibitively expensive.

Further to my description of my Home`s Utility Bills and your question - my House is `Semi Detatched` on a corner plot.

I will probably end up staying with my Electricity provider EDF at the end of October because I don`t want to pay by Direct Debit or `Manage my Account online`.

But as I previously described if / when I go for the Fixed Price Tariff October 2019 @ 19p per KwHr that will have been a 50% increase in KwHr price in the last 4-5 Years !

Chris

 

[Ric2013]

If the Cylinder and primary circuit pipework were causing the BIG discrepancy that you described in the amount of heat being produced by the Boiler compared to what should be required to bring the Cylinder water back up to the set temperature there would have to be a massive Heat loss happening somewhere - BUT I know that You will at least have a properly insulated Cylinder even if the primary circuit pipework is not insulated.

Chris: you will never offend me by asking technical questions, and I appreciate having someone who spares the time to bounce ideas around with me.

Reason I asked about your house is that my house, unlike yours, is centre terrace and the only section of solid wall still exposed is south facing and of small area, so the heat loss through it is obviously less great than on your house, as I suspected, but wanted to check.

The insulation on my cylinder is only 20mm thick, but I don't think that's the main problem. Thanks for making me look at this again, though as I've just done a little survey as I would if I were my own customer:

The cold feed isn't lagged (though it is not getting warm, so not the main cause)
The primary return is lagged, but the primary flow isn't. Since the primary flow runs down before reaching the cylinder, it does seem that the primary cold feed, vent, and pump are getting warmed by the cylinder, which cannot be a good thing. (I'd never considered the primary flow as a loss of heat before on this system.)
The expansion pipe is 13" long, not the 18" or 450m/m it should be and there is some parasitical warming of the secondary vent.

My shower is electric as all my cold water is direct from mains.

Last night I closed the isolator to the cylinder feed cistern at around 20.30, after the cylinder stat was satisfied. While water is being heated from 19.00 today, I will open that isolator and read my water meter to see exactly how much hot water has been drawn and then, again, check the gas used to reheat the cylinder against hot water usage (including running cold from dead legs) over the last 24 hours.

I suspect there IS a lot of limescale in the boiler heat exchanger. I also suspect there is a lot of limescale on the secondary side of the coil inside the cylinder.

Ebico doesn't officially accept cheques either. However, it was only when they changed their supplier from SSE to Robin Hood Energy, that this became the case. I pulled them up on this as I had always paid them by cheque and so I have a special agreement with them that I can pay by cheque. I see your point about price rises in your case. Not a fan of fixed rates myself, but we're all different.

 

[CHRISX]

Chris: you will never offend me by asking technical questions, and I appreciate having someone who spares the time to bounce ideas around with me.

Reason I asked about your house is that my house, unlike yours, is centre terrace and the only section of solid wall still exposed is south facing and of small area, so the heat loss through it is obviously less great than on your house, as I suspected, but wanted to check.

The insulation on my cylinder is only 20mm thick, but I don't think that's the main problem. Thanks for making me look at this again, though as I've just done a little survey as I would if I were my own customer:

The cold feed isn't lagged (though it is not getting warm, so not the main cause)
The primary return is lagged, but the primary flow isn't. Since the primary flow runs down before reaching the cylinder, it does seem that the primary cold feed, vent, and pump are getting warmed by the cylinder, which cannot be a good thing. (I'd never considered the primary flow as a loss of heat before on this system.)
The expansion pipe is 13" long, not the 18" or 450m/m it should be and there is some parasitical warming of the secondary vent.

My shower is electric as all my cold water is direct from mains.

Last night I closed the isolator to the cylinder feed cistern at around 20.30, after the cylinder stat was satisfied. While water is being heated from 19.00 today, I will open that isolator and read my water meter to see exactly how much hot water has been drawn and then, again, check the gas used to reheat the cylinder against hot water usage (including running cold from dead legs) over the last 24 hours.

I suspect there IS a lot of limescale in the boiler heat exchanger. I also suspect there is a lot of limescale on the secondary side of the coil inside the cylinder.

Ebico doesn't officially accept cheques either. However, it was only when they changed their supplier from SSE to Robin Hood Energy, that this became the case. I pulled them up on this as I had always paid them by cheque and so I have a special agreement with them that I can pay by cheque. I see your point about price rises in your case. Not a fan of fixed rates myself, but we're all different.

Hello again Ric2013,

The more that I think about your description that your Boiler is using far more Gas than it should be to heat your Hot Water Cylinder the more I think that is can only be being caused by excessive Limescale within the Boiler`s Heat Exchanger and as You mentioned probably a large build up of Limescale on the Cylinder Coil.

In my theory - the Boiler burners are having to fire for much longer than they should have to in order to heat the system water - through a layer of Limescale in the Heat Exchanger - which in turn then circulates around the Cylinder coil which because it also has a thick layer of Limescale slows down the Heat up of the Hot Water and in turn also causes the Boiler to be firing for much longer than it should to Heat the Hot Water in the Cylinder whatever amount of water is required to be reheated.

With regard to pipe insulation - as We know ideally the Primary Flow & Return should be well insulated and the Hot Water Service pipework.

Having written that - I have all of my Hot Water pipework well insulated from the Cylinder to almost every outlet - under the Baths - inside Vanity Units and Sink Units.

BUT - it only takes a metal Tap to gradually dissipate the Heat from each pipework `Leg`.

When we draw off some Hot Water that section of insulated pipe is obviously full of Hot Water - then the Heat starts dissipating by rising up to gently heat the metal Tap after a while the heat in that section of pipe will have gradually risen up to the Tap - irrespective of how well insulated the Hot Water pipework is.

Obviously an uninsulated Hot Water Service would lose the heat from the Hot Water much quicker but in the case of Bath / Shower pipework which might not be used again for hours what difference is there whether that section of Hot Water pipework loses the usable heat in 20 minutes or 40 minutes [guesstimates] ?

When I asked about your Hot Water usage shortly after posting the message I realised that You probably had an Electric Shower but I did not have time to Edit the message until much later by which time I guessed that you might have seen what I wrote so I left it.

When I wrote that I did not want to pay my Electricity Bills by Direct Debit or `Manage my Account online` I want to `Pay on receipt of Bill` in Cash at a local Paypoint or Post Office - something that they do not want people to do so a higher KwHr rate is charged.

Chris

 

[Ric2013]

Well, I've read my water meter having now opened the isolation valve, so my hot water usage (this obviously includes the dead legs, but that is correct as I wish to identify how much hot water has left the cylinder) has been: 17 litres.
I have used 0.68 cu m of gas, which is about 7.5 kWh, to reheat the cylinder.
7.5kW to heat 17 litres of water, plus make good any heat lost in storage, plus any system or boiler inefficiencies, some of which heat my home, which, in winter, cannot really be considered a waste.

So 441W per useful litre, heated through 50°C
At 78% efficiency, it should should take 75W per litre!

Re Ebico, I switched to them years ago because they are a not-for-profit and (used to) charge exactly the same regardless of payment method. Think it's changed a bit, but it still seems far more ethical than the Big 6 and they now buy from Robin Hood Energy, owned by Nottingham Council (IIRC). For some reason it is cheaper for me to buy from Ebico than directly from Robin Hood!

 

[Ric2013]

Okay, so I turned my water heating off on Friday night for some reason, after it had heated my cylinder. Today, the water was lukewarm and I fired up the boiler. It used 0.889cu m of gas, or 9.8kWh to heat the cylinder.

Bouncing idea about, if we say a conservative estimate of double the heat required, we would expect to see a proportional increse in gas used. Doubling the heat requirement has resulted in only 30% extra gas consumption.

Would it therefore seem reasonable to say that, in all likelihood, the inefficiency is quite possibly that the system requires a certain amount of heat to heat the primaries and cast iron heat exchanger?

This theory could be tested by testing the gas required to heat hot water, when the boiler is already hot from having been used for heating, if winter ever comes, that is!

 

[CHRISX]

Okay, so I turned my water heating off on Friday night for some reason, after it had heated my cylinder. Today, the water was lukewarm and I fired up the boiler. It used 0.889cu m of gas, or 9.8kWh to heat the cylinder.

Bouncing idea about, if we say a conservative estimate of double the heat required, we would expect to see a proportional increse in gas used. Doubling the heat requirement has resulted in only 30% extra gas consumption.

Would it therefore seem reasonable to say that, in all likelihood, the inefficiency is quite possibly that the system requires a certain amount of heat to heat the primaries and cast iron heat exchanger?

This theory could be tested by testing the gas required to heat hot water, when the boiler is already hot from having been used for heating, if winter ever comes, that is!

Hello again Ric2013,

I notice that You have not commented on my previous question about whether you have lived in your Home since the Boiler was installed and whether it is likely that your Heating system has always had Corrosion Inhibitor correctly dosed within it ?

Also as I mentioned even if it has had the Inhibitor a Boiler of that age is bound to have significant Limescale within its cast iron Heat Exchanger because the Inhibitor is not a `Preventor` re. Corrosion & Limescale.

IF there is a significant layer of Limescale within the Boiler Heat Exchanger the burners are having to `heat through` the Limescale to heat the water that is flowing through the Cylinder coil / Heating the Hot water.

In that scenario there would be a significant amount of additional Gas used to `Heat the cast iron Heat Exchanger and Primary Flow & Return water` and consequently the Water in the Cylinder.

Here is a quote from Fernox about Limescale within a Boiler Heat Exchanger:

QUOTE:

While the presence of limescale within a heating system is not as visually apparent to the average homeowner as it is in everyday kitchen appliances, its existence is just as prominent and harmful. Limescale deposits within a heating system can cause blockages in pipework and the boiler’s heat exchanger, significantly impacting on the system’s efficiency. This forces the boiler to work harder than necessary to produce the desired temperature and can eventually lead to the premature failure of system components.

In fact, the presence of limescale in a boiler greatly inhibits heat flow within the home and is one of the main causes of spiralling fuel bills.

With limescale conducting thermal heat at a rate 400 times less efficient than the copper piping, even a 1/16 of an inch deposit of scale around a boiler’s heating elements can increase fuel costs by up to an alarming 15%.

END OF QUOTE

I could easily imagine a Boiler from the 1980`s having far more than 1/16th of an inch of Limescale - probably more than 1/8th of an inch even if there has been Corrosion Inhibitor in the system all of the time.

I could be wrong about this but I don`t think that 1/8th of an inch of Limescale would equate to only about a 30% increase in Gas to heat the water flowing through the Heat Exchanger - it could be much more than an additional 30% ?

I don`t think that the inefficiency would just increase in multiples of 15% for every 1/16th of an inch that the Fernox quote mentions ?

I wonder why Fernox are using `1/16th of an inch` as a measurement ?

Here is the Fernox webpage where the Quote came from:

HARD WATER, SIMPLE SOLUTION - Fernox UK

Chris

 

[Ric2013]

Chris,

Sentinel claims it protects against both corrosion and limescale, but you are right that the boiler pre-dates me by 20 years, during which period we have no idea how much inhibitor (if any), or what kind, was in place. I would imagine Fernox is similar. In any case, the boiler kettles, so that would suggest scale is present.

I accept your point that inhibitor is probably not 100% effective (if I understand you correctly) and I have a lot of scepticism with regard to claims made by inhibitor firms.

I hope you can see that the 30% I am referring to above is not the 30% you are referring to. They are two separate 30% figures.

The point I was making is that, even if we accept the boiler efficiency has fallen to 25% or whatever due to limescale (though I am highly sceptical the efficiency could fall to that level before the heat exchanger burns through), then, by doubling the amount of heat required by my DHW cylinder (by letting it run cold), we would expect the gas input required by the boiler to double, whereas it has actually only increased by 30% respective to re-heating a largely warm cylinder. This suggests to me that my original 7.5kWh to reheat a fairly hot cylinder is not only down to boiler inefficiency.

Regarding the 1/16" claim, if a sixteenth of an inch provides x insulation (resistance to heat transfer), then an eighth naturally provides 2x insulation. Couple, though with the insulation of the iron itself, and each doubling of the scale thickness should, theoretically, increase the insulation by a little less than a doubling.

The point I was making is that the primary circuit is composed of about 11 litres of water in the primary circuit and boiler, (and some in the cylinder coil) and around 40kg of cast-iron in the heat exchanger. As such, the primary circuit requires the equivalent of however much heat is needed to heat 15l of water from 20 to 80 degrees, before it is heated through. Which doesn't explain a lot, given that it's little over 1kW, though it's worth testing this theory.

In any case, I've cancelled work as suffering from flu, but I'm getting bored and will probably whip the immersion heater out at some point tomorrow and see what state the inside of the cylinder is in. Can always do a few minutes at a time, eh?

 

[Ric2013]

Well, the hardest thing was having enough strength to coil the poxy hose back up after I'd drained the cistern. Realise now there was no need to drain the cistern, but obviously thought processes not at maximum levels!

The cylinder was also empied. There is a thin coating on the coil, but it looks to be relatively minor, though I appreciate that the thickness of scale is hard to assess. I think I'll dump some citric acid solution in the cylinder and see if I can dissolve some of the limescale, and hope this won't wreck the cylinder! Apart from some none-too-impressive pipe bending inside the cylinder, it seems relatively in order.

Also, a drained cylinder allowed me to test the heat required to heat the primary circuit. Gas input required is 2.28kW before the boiler thermostat switched off. This is interesting. While it could mean the boiler is <50% efficient, assuming my guestimates of heat required by the primary circuit are accurate, it also means that, in summer, the boiler has to use as much gas as, burned efficiently, would be needed by the DHW cylinder (heating the whole cylinder through 15°C requires 2kW) just to get the primaries heated.

 

[CHRISX]

Well, the hardest thing was having enough strength to coil the poxy hose back up after I'd drained the cistern. Realise now there was no need to drain the cistern, but obviously thought processes not at maximum levels!

The cylinder was also empied. There is a thin coating on the coil, but it looks to be relatively minor, though I appreciate that the thickness of scale is hard to assess. I think I'll dump some citric acid solution in the cylinder and see if I can dissolve some of the limescale, and hope this won't wreck the cylinder! Apart from some none-too-impressive pipe bending inside the cylinder, it seems relatively in order.

View attachment 34919

Also, a drained cylinder allowed me to test the heat required to heat the primary circuit. Gas input required is 2.28kW before the boiler thermostat switched off. This is interesting. While it could mean the boiler is <50% efficient, assuming my guestimates of heat required by the primary circuit are accurate, it also means that, in summer, the boiler has to use as much gas as, burned efficiently, would be needed by the DHW cylinder (heating the whole cylinder through 15°C requires 2kW) just to get the primaries heated.

Hello Ric2013,

The Cylinder looks fine, how old is it ?

As You know a `badly scaled` Cylinder would have not only much more Limescale on the Coil but also there would be Limescale debris in the bottom where it had broken off the Coil.

It is very interesting when the results of `experiments` like you have just done are available because we very rarely get to see the figures from a physical `Test`.

How much water do You calculate is contained in the Primary pipework and the Boiler Heat Exchanger ?

Obviously the Boiler Heat Exchanger Limescale level is unknown regarding how much additional heat is used to `heat through` any scale.

Chris

 

[Ric2013]

Hi Chris (and whoever else is reading),

The cylinder was there in 2006. How much older than that, I do not know.

Well, yes, I am surprised there is not a collection of limescale flakes at the base. Not bad for its age. I've taken out cylinders that are perhaps 50 years old, but this was not even a tenth as much limescale.

Thank you. I find it interesting to see how things work in real world situations, and I'm glad you appreciate the sharing. It would be interesting to compare how other systems of this kind are functioning. I do have a couple of friends/family/customers who might let me run the experiment, but I digress.

The primary pipework is around (2 x 7m of 22mm) 4.5l, and heat exchanger water content is another 6l. Round the total to 11l and it shouldn't be far off.

Given that the F&E was not covered and therefore subject to increased evaporation when I bought the place, I would imagine there is very likely to be quite a lot of limescale in the boiler.

 

[Ric2013]

Well, 500grammes of citric acid powder dissolved in water and then filled to the top of coil and heated through did indeed remove the limescale, so it must have been quite a thin layer. As expected, this made little difference to performance.

 

[CHRISX]

Hello Ric2013,

I would still be looking at the Boiler being heavily scaled.

I feel that the calculated excessive amount of Gas to heat your Cylinder / Hot Water can only be attributed to it having to heat the water in the Primary loop through a layer of Limescale.

If as I suspect there is a significant layer of Limescale within the Boiler Heat Exchanger that would be absorbing a significant amount of heat from the burners before the heat is actually heating the water that flows through the Cylinder coil.

I cannot see anywhere else that the amount of `Heat loss` that You previously described could be lost - it cannot be being lost from the Primary Flow & Return ?

Chris

 

[Chuck]

I've never done a decent heat calc but when the old Mexico finally dies I will do because having a boiler that's oversized is very inefficient due to cycling.

You've probably thought of this, but...

While you're waiting for your boiler to die, make a note of the average external temperature and how much fuel it consumes (daily) during a spell of cold weather. This information will give a reassuring sanity check for your calculations.

 

[Welder]

There is software now that does a certified heat calc for you at £10 or less per pop. No need to do any measurements yourself. I'll look it up and post.

For any heating installers it looks a no brainer cos it makes sure everything is sized perfectly so minimal cycling and maximising reliability...

 

[Welder]

Www.Heat-engineer.Com

 

[ShaunCorbs]

Costing too much for me 10 per report is way too much and the monthly cost is too high for me

 

[Welder]

Costing too much for me 10 per report is way too much and the monthly cost is too high for me

The monthly includes unlimited fully warranted reports... Surely being able warrent a smaller boiler & its consumption savings & more effectiveness is worth £10 to a customer over, at best, a bloomin guess!?

 

[ShaunCorbs]

The monthly includes unlimited fully warranted reports... Surely being able warrent a smaller boiler & its consumption savings & more effectiveness is worth £10 to a customer over, at best, a bloomin guess!?

If your doing a lot of commercial new build I could see it but domestically mr combi app works or the mears calc for next to no cost