Deciding between a combi-boiler or a condensing boiler

mrcheez · 06-01-2013 3:11pm #1

Our house is a 2 bed house with one bathroom. There is an old cold water tank in the attic taking up a large chunk of room, and an old hot water cylinder in the hot press with a (loud) analogue timer.

I want to get the boiler upgraded with a high-efficiency one and it would be great to get some help determining if I should go for a combi-boiler or condensing boiler...

- My plumber suggested I should get a new condensing boiler, and update the water tank/hot water cylinder, rather than go for the combi-boiler. Is there any reason why a combi-boiler might not be suitable for my house? Water pressure? Is it a bigger job to install a combi-boiler and remove the existing setup?

- If I went for a combi-boiler am I correct that I can disconnect the water tank in the attic (potentially cut it up later with a jigsaw) and remove the hot water cylinder?

- Is a condensing boiler cheaper to run than a combi, or vice versa?

- Is a condensing boiler cheaper to buy than a combi, or vice versa?

- Can I run a power shower with a combi-boiler?

- If I decided to go for the condensing boiler, my plumber suggested that I should keep the analogue timer rather than replace it with a digital one (due to water pressure apparently?!?). Is there any reason why I couldn't get a digital timer that would be silent?

Lastly, should I bother with the SEAI grant for this upgrade? All I see on the forums are plumbers complaining that it requires the customer to pay for more than they need. This true?

Thanks!

DGOBS · 06-01-2013 3:49pm

You can have Cobh that is a high efficiency condensing boiler
But if your have mutiliple draw off points and showers the vast majority of combo boilers wouldn't cope with it

mrcheez · 06-01-2013 4:54pm

Hi, thanks for the reply. There's only one shower and two taps (one in the bathroom, one in the kitchen) so not too many draw off points afaik

corkgsxr · 06-01-2013 5:13pm

If you're water pressure is decent I couldn't see why not. I love combis myself.

And there both condensing.

mrcheez · 06-01-2013 5:25pm

corkgsxr wrote: »

And there both condensing.

Ah ok, I thought that there were 2 types of combi (non-condensing and condensing).

corkgsxr · 06-01-2013 5:30pm

mrcheez wrote: »

Ah ok, I thought that there were 2 types of combi (non-condensing and condensing).

Not any more, all new boilers sold have to be condensing

DGOBS · 06-01-2013 5:59pm

not only just condensing, make sure the are rated band A

JohnnieK · 06-01-2013 7:30pm

You can also apply for an SEAI grant if you choose a combi. The grant is worth €560 to you. You don't nesseseraly have to tear the place apart when putting a combi in. There are some cases out there that require extensive re configuring of the system to enable an upgrade and this makes the process un economical in respect to the time it takes to get your return.

You need to get a survey done to way up the options.

Dtp79 · 06-01-2013 7:44pm

mrcheez wrote: »

Our house is a 2 bed house with one bathroom. There is an old cold water tank in the attic taking up a large chunk of room, and an old hot water cylinder in the hot press with a (loud) analogue timer.

I want to get the boiler upgraded with a high-efficiency one and it would be great to get some help determining if I should go for a combi-boiler or condensing boiler...

- My plumber suggested I should get a new condensing boiler, and update the water tank/hot water cylinder, rather than go for the combi-boiler. Is there any reason why a combi-boiler might not be suitable for my house? Water pressure? Is it a bigger job to install a combi-boiler and remove the existing setup?

- If I went for a combi-boiler am I correct that I can disconnect the water tank in the attic (potentially cut it up later with a jigsaw) and remove the hot water cylinder?

- Is a condensing boiler cheaper to run than a combi, or vice versa?

- Is a condensing boiler cheaper to buy than a combi, or vice versa?

- Can I run a power shower with a combi-boiler?

- If I decided to go for the condensing boiler, my plumber suggested that I should keep the analogue timer rather than replace it with a digital one (due to water pressure apparently?!?). Is there any reason why I couldn't get a digital timer that would be silent?

Lastly, should I bother with the SEAI grant for this upgrade? All I see on the forums are plumbers complaining that it requires the customer to pay for more than they need. This true?

Thanks!

Get a hardness test done on your water. Limescale loves combis
Plus I don't see what a timer has to do with water pressure either

TPM · 06-01-2013 8:54pm

mrcheez wrote: »

Our house is a 2 bed house with one bathroom. There is an old cold water tank in the attic taking up a large chunk of room, and an old hot water cylinder in the hot press with a (loud) analogue timer.

You can replace the "(loud) analogue timer" with a silent digital one regardless of whatever work/changes you are going to make.
The timer is most likely for the immersion, with a combi boiler you wont have an immersion so no timer but also you wont be able to heat the water from the electricity if the boiler breaks down or you run out of oil(if its oil and not gas)

mrcheez wrote: »

I want to get the boiler upgraded with a high-efficiency one and it would be great to get some help determining if I should go for a combi-boiler or condensing boiler...

As already said you can get a condensing combi boiler, and you need to determine if you want a combi or normal boiler

mrcheez wrote: »

- My plumber suggested I should get a new condensing boiler, and update the water tank/hot water cylinder, rather than go for the combi-boiler. Is there any reason why a combi-boiler might not be suitable for my house? Water pressure? Is it a bigger job to install a combi-boiler and remove the existing setup?

A certain amount of this can be down to the plumbers preference and the actual conditions in the house.
As johnnie you could really do with getting a survey done to determine the amount of work and practicality of installing a combi boiler versus a standard one. Imo A big thing to consider is if you are on gas or oil, combi boilers are usually sized by the flow rate of hot water leading to the boiler being oversized for the heating, this is ok in a modulating gas boiler but not good in an oil boiler as it leads to short cycling and poorer efficiency.

mrcheez wrote: »

- If I went for a combi-boiler am I correct that I can disconnect the water tank in the attic (potentially cut it up later with a jigsaw) and remove the hot water cylinder?

Not really you will still need the tank in the attic for your cold water supply for the toilets, hand basins and bath.

you would be able to do away without the hot water cylinder.

mrcheez wrote: »

- Is a condensing boiler cheaper to buy than a combi, or vice versa?

- Can I run a power shower with a combi-boiler?

I am not sure with gas but I would think with the fact they are modulating there shouldnt be too much difference.
In my experience with oil the combi's tend to be more expensive to run

It could be possible to run a power shower off a combi boiler but you would have to check the flow rates, if the flow rares are very high you will require a very high out boiler which could be a fair bit more expensive

mrcheez wrote: »

- If I decided to go for the condensing boiler, my plumber suggested that I should keep the analogue timer rather than replace it with a digital one (due to water pressure apparently?!?). Is there any reason why I couldn't get a digital timer that would be silent?

There is no reason I can think of why you couldnt fit a digital timer specially when you will be getting all the other work done.

mrcheez wrote: »

Lastly, should I bother with the SEAI grant for this upgrade? All I see on the forums are plumbers complaining that it requires the customer to pay for more than they need. This true?

Thanks!

There is a lot of talk about installers charging extra for grant work, and of there is no need to do all that work.

In reality there is no reason you should be charged more for a job just because it is for an seai grant, it may be possible to do it cheaper with out the grand but this will because it will be less of a job (less zoning, controls, non listed appliances) but this could be a false economy.

Personally I prefer a normal boiler with a well insulated hot cylinder and proper controls and zoning because you still have a reserve of hot water in the event of a power failure, boiler breakdown, no oil/gas. You also get to have an immersion to heat the water if you cant with the boiler for some reason(admittedly only a small thing)
Plus I prefer servicing normal boilers because there is less in the casing:P

As with any job involving i reasonable amount of work/money get a few quotes and opinions on the suitability of each boiler for your needs and the plumbing in your house

mrcheez · 06-01-2013 9:44pm

cool thanks

06-01-2013 10:50pm

Good post TPM,

TPM wrote: »

Imo A big thing to consider is if you are on gas or oil, combi boilers are usually sized by the flow rate of hot water leading to the boiler being oversized for the heating, this is ok in a modulating gas boiler but not good in an oil boiler as it leads to short cycling and poorer efficiency.

without me sounding like a picky cantankerous old git but:) gas boilers can't be over sized if they are commissioned correctly, a combi can have it's heating output adjusted to match the required heat load, they can be adjusted from maximum output down to a few KW, so you can have a 38kw combi heating just a few rads or a big house without any short cycling issues, gas boiler with short cycling issues havn't been commissioned correctly.

TPM · 07-01-2013 1:00am

gary71 wrote: »

Good post TPM,

without me sounding like a picky cantankerous old git but:) gas boilers can't be over sized if they are commissioned correctly, a combi can have it's heating output adjusted to match the required heat load, they can be adjusted from maximum output down to a few KW, so you can have a 38kw combi heating just a few rads or a big house without any short cycling issues, gas boiler with short cycling issues havn't been commissioned correctly.

A valid enough point, which goes to enforce the benefits of gas specially when it comes to what can be a huge difference in heat requirements of heating and hotwater demand in combi boilers

and now its my turn to be a slightly picky cantankerous old git but:) lol
The way the gas burners modulate is great and due to this the burner output will only produce the heat that is required.
but technically speaking if you require 12 kw to heat the house and 38kw for the hot water demand, the actual boiler(not the heat produced by the burner) is oversized for the heating demand (you would never fit a 38kw boiler if you needed 12kw), this fact is almost negated by the modulating of the burner output though. Where as with oil this would be an issue and cause the short cycling that I was referring too

There is a big difference between the efficiency of a gas and oil combi (in favour of the gas) this is what i was pointing out but it may not hav read as clearly as it seemed in my head when I was typing.

@gary71 the point in your post is appreciated and taken in good spirit as my reply is intended

mrcheez · 07-01-2013 8:43pm

TPM wrote: »

Not really you will still need the tank in the attic for your cold water supply for the toilets, hand basins and bath.

A colleague of mine said that when he got his combi installed he was able to connect everything to the mains, including the toilet, and got rid of the tank in the attic.

Now I'm even more confuzzled!

This would suit me down to a T as storage space is a valuable commodity in my house and it would be great to have the entire attic free!

TPM · 07-01-2013 8:50pm

mrcheez wrote: »

A colleague of mine said that when he got his combi installed he was able to connect everything to the mains, including the toilet, and got rid of the tank in the attic.

Now I'm even more confuzzled!

This would suit me down to a T as storage space is a valuable commodity in my house and it would be great to have the entire attic free!

This would not be common practice, It may not even be allowed I think I heard something at one time that you are only suppose to connect the kitchen tap to the mains and nothing else. I am open to correction on this.
I know combi boilers themselves and mains electric showers this.

Regardless of the above, you could run into flow rate issues if everything is connected to the mains specially if the mains pressure drops.
You would also be completely without water for hand basins toilets etc. in the event of a mains water stoppage

mrcheez · 07-01-2013 9:45pm

Yeah it's rather odd as all the UK websites I've seen seem to recommend this method (and I'm aware that all new UK properties have to have combi boilers)... perhaps it's a newer idea in Ireland *shrug*

When a combi boiler is fitted its usual to remove the cold water storage tank in the roofspace and the hot water cylinder (usually in the airing cupboard). The primary purpose of the CWST is to replenish the HWC as hot water is drawn off.

The combi (fed by mains cold) heats hot water on an "on demand" basis so storage is no longer required. Normally all cold taps are converted to mains supply when a combi is fitted so storage is no longer required.

http://forums.moneysavingexpert.com/showthread.php?t=2816002

JohnnieK · 08-01-2013 8:27pm

If you go for the combi and keep the tank, remember that any mixing taps in te house won't mix as there will be unequal pressures. Hot will over ride the cold.

mrcheez · 09-01-2013 11:31am

JohnnieK wrote: »

If you go for the combi and keep the tank, remember that any mixing taps in te house won't mix as there will be unequal pressures. Hot will over ride the cold.

That's what I've read too. Why are there so many different opinions about something that should have a simple "Yes this is possible"

Some people say that I can do the above, others say it's not the norm, then even one guy said it's ILLEGAL to not have a tank in the attic.

WTF?!?

JohnnieK · 09-01-2013 12:35pm

mrcheez wrote: »

That's what I've read too. Why are there so many different opinions about something that should have a simple "Yes this is possible"

Some people say that I can do the above, others say it's not the norm, then even one guy said it's ILLEGAL to not have a tank in the attic.

WTF?!?

Water by-laws state that the only draw off to be connected to the incoming main is the kitchen sink and the CWST in the attic.

Its different in the uk and continent. I would imagine this will change when rates and quality of supply changes.

Another way around it would be a whole house booster being fed from the tank and feeding both the combi and the cold. The problem here is you are swaying away from the manufacturer's recommendations that it's connected to the mains, although i have not experienced any difficulty with manufacturer's as of yet.

I have done both ways and both work fine. Some people even put a tank fed electric shower in as a back up.

TPM · 09-01-2013 8:39pm

mrcheez wrote: »

That's what I've read too. Why are there so many different opinions about something that should have a simple "Yes this is possible"

Some people say that I can do the above, others say it's not the norm, then even one guy said it's ILLEGAL to not have a tank in the attic.

WTF?!?

Well just because something is possible doesnt mean its right or even allowed then on top of that because there are so many different ways of doing things with hugely varying costs a simple "yes that is possible" answer wouldnt really be a definitive answer to the question :P.
Then the fact that is Ireland an there seems to be an inherent feeling that rules are only there to hinder us and that they dont really mean what they say.

But yea it is hard to get an answer to most things, there are some good lads here with good advice (which will be of varying opinions) that will help you decide what you want and to pick a tradesman that can deliver.

At the end of the day there is little or no regulation or enforcement in Ireland leaving self regulation :rolleyes:

mrcheez · 09-01-2013 8:53pm

With so many completely diverse answers to the same question it's daunting for the newcomer to say the least

TPM · 09-01-2013 9:25pm

mrcheez wrote: »

With so many completely diverse answers to the same question it's daunting for the newcomer to say the least

and frustrating specially when people are doing what you would like to do even though it is not permitted.

just take your time and think things through

oxygen · 12-08-2013 2:47pm

mrcheez wrote: »

Our house is a 2 bed house with one bathroom. There is an old cold water tank in the attic taking up a large chunk of room, and an old hot water cylinder in the hot press with a (loud) analogue timer.

I want to get the boiler upgraded with a high-efficiency one and it would be great to get some help determining if I should go for a combi-boiler or condensing boiler...

Thanks!

Hope I dont get grief for bumping an old thread. What did you do after MrCheez? I seriously weighing up this option to get rid of the cylinder in my bedroom. Its an old house, so there isnt a specific airing cupboard. I would love to get rid of the cylinder and create some extra space.

mrcheez · 12-08-2013 5:33pm

Yeah no worries ... I probably changed my spec from the original thread as I learned more (and got suggestions from various plumbers/posters!)

Basically I:
- Got rid of water tank in attic
- Got rid of hot water cylinder in hot press
- Built new boiler house in garden to house new water tank / pump / Worcester Bosch COMBI boiler

Now I have one hell of a powerful shower, hot water on demand, and lots of free space in house/attic (only thing I'm dreading is the water bill when this starts

)

mattia · 15-08-2013 11:59am

Hello Everyone,
I was following this forum as we are about to plan for a big boiler change. I am still not decided, but my partner is stubborn for a combi.
I just wanted to ask where can I find information about water connection rules? What I mean…I need to make sure that getting rid of the attic tank and connecting everything to the mains is a legal thing in Ireland. I know for sure it is in my country

Thank you,
mattia

JohnnieK · 15-08-2013 12:37pm

Your local council will have by-laws that you can ask for. The letter of the law in most case's is that only one other draw off point other than that of the cold storage tank is allowed. So it shouldn't be connected to the mains, unless a direct system is already in the house.

You could look at a whole house booster fed from the tank. That's the way mine is done.

mattia · 15-08-2013 12:55pm

Hi JonnieK,
Is you kitchen cold water fed from the tank as well?

mrcheez · 15-08-2013 1:02pm

mattia wrote: »

Hello Everyone,
I was following this forum as we are about to plan for a big boiler change. I am still not decided, but my partner is stubborn for a combi.
I just wanted to ask where can I find information about water connection rules? What I mean…I need to make sure that getting rid of the attic tank and connecting everything to the mains is a legal thing in Ireland. I know for sure it is in my country
Thank you,
mattia

I was going to connect to the mains, but water pressure wasn't quite good enough to work alone, so I went with a new tank and pump combination, but placed at the rear of the house in a boiler house.

You might be able to forego the tank/pump if your water pressure is high but Ireland's infrastructure is a bit behind other countries (as I was told by several different plumbers).

JohnnieK · 15-08-2013 1:09pm

mattia wrote: »

Hi JonnieK,
Is you kitchen cold water fed from the tank as well?

My kitchen cold is from the mains.

mattia · 15-08-2013 1:11pm

The thing is that I am pretty much sure that our boiler is very old and it heats only rads. We have hot water form electricity. We still didn’t get a first bill, but I am already worried. I don’t have personal preferences regarding tank-less or tank-full water system, as long as it works efficiently and properly. I am organizing for our plumber to come and inspect the system and based on that we will move forward. We need to change the HWC as well if we go for a regular boiler and we will need to install the pump to bust pressure. And at the moment our shower and bath is on gravity pressure only.
My partner hates waiting for hot water to be available and that is the main problem. And there is no way you can argue with her

How big is a boiler house? Is it brick or wooden? How tall it is?
Thanks!

mattia · 15-08-2013 1:13pm

JonnieK,
Do you have a problem with the pressure imbalance between hot and cold water?

mrcheez · 15-08-2013 3:03pm

If the taps in your kitchen are attached to the mains (they should be to make it drinkable!), then you can tell what sort of water pressure you have, although best to get a plumber's opinion.

The boiler house is large enough for a tank, boiler and pump. About 1.5 metre high by 4 metre long. It's brick, it has to be to support the boiler, plus I've got insulation/plugs to allow me to run a heater if weather goes freezing. Don't want the tank freezing up!

Pressure imbalance isn't a problem if you have all water fed through the pump (apart from the supply to the kitchen - taps/dishwasher which runs off the mains)

The combi is the best solution if you want hot water on demand, but retaining a tank is a good idea as a backup in case water supply cut off etc. My solution was pricey, but see if a plumber can suggest something similar.

JohnnieK · 15-08-2013 3:05pm

mattia wrote: »

JonnieK,
Do you have a problem with the pressure imbalance between hot and cold water?

You won't at the kitchen sink as most kitchen mixers are mixed at the spout instead of the valve body.

My system is not connected to the mains anyway it's fed through a booster so I have equal pressures all over the house.

mattia · 15-08-2013 3:13pm

mrcheez,
Thanks a lot.

I am getting few people organized to see our system and advise on the upgrade.

JonnieK,
Thank you.
We still have some time before getting the job done. I will get all infor togetther and the we will decide

Parraig · 03-09-2013 10:32pm

Whatever the regulations, I feel that all cold taps should be fed from the mains.

Nobody has discussed the purity of the water from the storage tank in the attic!

I once found a swarm of mouldy bees in a tank - they had come in the overflow pipe and died in the tank.

Last week I ran my storage tank dry by filling the bath repeatedly -
all sorts of beasties appeared at the end.

The thought of cleaning my teeth with this, or drinking it is pretty awful.

Now none of my relations will clean their teeth at the bathroom taps.

shane0007 · 03-09-2013 10:42pm

You should have a lid on your cold water storage tank. This would be standard practice in my books.
Mains throughout all taps would just not make sense.
One, no water during outage, two, unbalanced hot & cold taps, especially mixers, three, water bye-laws would not permit.

mattia · 04-09-2013 10:29am

I heard that tank water can be terrible, but I agree with Shane0007 that lid should sort most of the problems out.

I am getting my head around all that water/ boiler/ etc. issues. I will have couple of plumbers come over and diagnose/check our heating/water system.

I wanta good, reliable system (tankless or with tanks) with good water pressure. To achieve that we will chose the best of the solutions without breaking the law.

The last thing I need is a fight with city council or similar. We have to much to do with our place

shane0007 · 04-09-2013 10:33am

Use a potable water storage tank feeding a booster pump.

JohnnieK · 04-09-2013 11:58am

Best pressure would be tank and booster.

Deciding between a combi-boiler or a condensing boiler

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