Combi boiler or condensing boiler:pros and cons?

tea and coffee

:eek: Have to decide by Monday.

Didn't even know about combi boilers til 4pm yetsterday, so need a 101 on those.

We are renovating, and had just planned for a condensing boiler to replace an enourmous (think seperate boiler house) oil boiler. The issue is that the house isn't zoned and to do so requires a full replumb

The plumber says he can zone of the hot water, because to have to turn on the whole system in the summer would be a p.i.t.a. just for hot water. He then suggested a combi boiler with a pump.

So far cost would be about the same as I wouldn't have to get an electric shower installed as planned, with the combi boiler.

Condensing:
Pros:
- Cheaper to buy/install
- No running out of water if mains cut off
- Plumber can zone off hot water (at extra cost)

Cons:
- Need to get electric shower
-Our hot water cylinder is small and think water tank in attic is small also for size of house/family, so prob need replacing if not now, at some stage.
- Heating or immersion need to be phyiscally turned on for hot water (and kids leave stuff like that on :mad: )

Combi:
Pros:
- Instant hot water
- No electric shower needed
- House is effectively zoned by virtue of this boiler
- No more "did you switch off the immersion" or running out of hot water or remembering to turn it on to get hot water.

COns:
- Noisy pump whining at all hours when anyone uses any water
- More expensive to buy/install
- If water main is off, we have no water, not even hot from tank.
- we have one less shower in the house because we dont have the leccy shower. (one this point, is it possible to keep the hot water tank/electric shower in case of mains cut off, or to have leccy shower as a back up or is it superfluous?)

Anyone any advice?
Thanks

tea and coffee

"Combination boilers provide both instant hot water and central heating, but not at the same time. They have a 'hot water priority', which means that when hot water is being run there is no heat output to the radiators. They also struggle when a demand for hot water is made from more than one outlet at the same time - such as a shower and a sink tap - because the hot water flow rate is divided by each water source used at the same time. Also, you cannot boost the water pressure to a shower by adding a shower pump when a gas combi boiler is installed. "

Is the above all true? Surely you can attach a pump to boost the rubbish Irish pressure?
That article also says they are dearer to repair and dont last as long as condensing boilers. True?

Outkast_IRE

tea and coffee wrote: »

"Combination boilers provide both instant hot water and central heating, but not at the same time. They have a 'hot water priority', which means that when hot water is being run there is no heat output to the radiators. They also struggle when a demand for hot water is made from more than one outlet at the same time - such as a shower and a sink tap - because the hot water flow rate is divided by each water source used at the same time. Also, you cannot boost the water pressure to a shower by adding a shower pump when a gas combi boiler is installed. "

Is the above all true? Surely you can attach a pump to boost the rubbish Irish pressure?
That article also says they are dearer to repair and dont last as long as condensing boilers. True?

You aren't meant to attach a pump to the mains to try and boost the pressure, some people do and they are ****, your basically making it worse for you neighbours to provide for yourself.

The pressure isn't rubbish in all areas, you need to get it checked. I have been in areas with over 3 bar mains pressure no problem.

As for lifespans of combi boilers, I know people with ones that are 10 years old and more and there have been no major issues. As far as I know most boilers will prioritise the hot water but that's not much of an issue, sure if someone jumps in for a shower the rads not heating for 10 mins wont make a huge difference.

tea and coffee

Thanks. I see, just plumber recommended the pump. I see what you mean though. I don't know the pressure. I asked the plumber and he doens't know either. I presume its easy enough to check something like that, is it?

MiniGolf

tea and coffee wrote: »

"Combination boilers provide both instant hot water and central heating, but not at the same time. They have a 'hot water priority', which means that when hot water is being run there is no heat output to the radiators. They also struggle when a demand for hot water is made from more than one outlet at the same time - such as a shower and a sink tap - because the hot water flow rate is divided by each water source used at the same time. Also, you cannot boost the water pressure to a shower by adding a shower pump when a gas combi boiler is installed. "

Is the above all true? Surely you can attach a pump to boost the rubbish Irish pressure?
That article also says they are dearer to repair and dont last as long as condensing boilers. True?

I have sent you a PM.

Outkast_IRE

tea and coffee wrote: »

Thanks. I see, just plumber recommended the pump. I see what you mean though. I don't know the pressure. I asked the plumber and he doens't know either. I presume its easy enough to check something like that, is it?

Yes a pressure guage and a few fittings attached to the mains supply into your house would tell you.

If the pressure is poor I would usually recommend a storage cistern in attic and hot water cylinder in hotpress.

Also avoid extra pumps where you can, if you use a pump on the mains it doesn't run for free there is an electrical cost, and it will need to be maintained or replaced down the line. Whereas with a storage cistern the mains pressure is doing the work for you initially to get it to the cistern(tank) , and gravity ( or a pump) can be used to supply your hot and cold water then. You wouldn't need electric showers if you got a properly sized hot water cylinder and get a separate pump for your shower, and leave the toilet and basin work off gravity, the shower pump could be put in the hot press too if theres room. All that would be on display in the shower area then is the mixing valve and shower head.

tea and coffee

Combi boilers find it hard to do more than one shower at the same time, right? So if we were running the kitchen taps and the two showers and the dishwasher , for example would it struggle? Or would I need a ma-hoosive yoke as opposed to the same condensing boilers?

I am that confused and have to go tile shopping now. >:-(

Outkast_IRE

tea and coffee wrote: »

Combi boilers find it hard to do more than one shower at the same time, right? So if we were running the kitchen taps and the two showers and the dishwasher , for example would it struggle? Or would I need a ma-hoosive yoke as opposed to the same condensing boilers?

I am that confused and have to go tile shopping now. >:-(

Ok modern dishwashers tend not to have a hot water supply, some of the old ones still might, but I haven't seen one in a while now, the same can be said for modern washing machines.

I don't know why you would need to run 2 showers at the same time as well as the kitchen tap, unless your a B&B or hotel, I would imagine even in a family home the event is rare enough. That being said if you feel this sceanario is likely to happen to you often, then I would recommend getting properly sized storage cistern (tank) in the attic as well as a properly sized hot water cylinder.
And get a shower pump to run the 2 showers, leave the sinks and toilets work off gravity.

DGOBS

Rule of thumb, more than one bathroom, avoid a combi

tea and coffee

Thank you. We have 5 kids, so I imagine that at school time they will want to shower at the same time. LOL.
In the above scenario, are you referring to getting a condensing boiler or a condensing combi boiler?

Thanks

Dtp79

tea and coffee wrote: »

Thank you. We have 5 kids, so I imagine that at school time they will want to shower at the same time. LOL.
In the above scenario, are you referring to getting a condensing boiler or a condensing combi boiler?

Thanks

How many showers in your house?

Outkast_IRE

tea and coffee wrote: »

Thank you. We have 5 kids, so I imagine that at school time they will want to shower at the same time. LOL.
In the above scenario, are you referring to getting a condensing boiler or a condensing combi boiler?

Thanks

Ok 5 kids is larger than the average modern day family, you should mention that at the start most hot and cold water systems are designed on occupancy levels

Avoid the combi is my opinion so.

As I said if I was looking at designing this system for you, I would be leaning toward the following setup.

1. A hot water cylinder sized to deal with what will be a larger than normal demand.
2. Zone the heating as suggested, with hot water as a separate zone.
3. Size the attic cold water cistern correctly, for the amount of people in the home. If the mains pressure is in any way poor it will be critical that the cold water cistern is sized correctly so it doesn't empty fully.
4. Connect the two showers to an appropriately sized shower pump, just be aware if there is two people showering at once the pressure wont be as good, and you are going to use a large volume of hot water.
5. Leave the toilets and sinks work off of gravity i.e no pump. this will ensure the shower pump is only for the showers. and therefore if someone flushes a loo at night it wont come on etc.

With regards to the shower pump you can get ones which are made to cater for multiple outlets(showers) check the prices of these as they may be worth the investment if its likely multiple showers are going at the same time.
But as I said you need a correctly sized cylinder and correctly sized cold water cistern.

tea and coffee

Thanks all.
To whoever asked how many showers: 1 downstairs gravity fed. ..or possibly on the pump.
1 upstairs on a pump. Then a hose head in the same bathroom for the bath -for washing out bath or rinsing dog. And leccy shower in bath for when kids take all the hot water.

The leccy shower i picked is a bit wanky, I fully admit. Its a Triton but runs off mains or tank so will likely need a pump. Will try it without first, but will probably have to get one.

Think I will have to get a larger tank so. Its very small.

Outkast_IRE

tea and coffee wrote: »

Thanks all.
To whoever asked how many showers: 1 downstairs gravity fed. ..or possibly on the pump.
1 upstairs on a pump. Then a hose head in the same bathroom for the bath -for washing out bath or rinsing dog. And leccy shower in bath for when kids take all the hot water.

The leccy shower i picked is a bit wanky, I fully admit. Its a Triton but runs off mains or tank so will likely need a pump. Will try it without first, but will probably have to get one.

Think I will have to get a larger tank so. Its very small.

You need a good professional, you may not need a larger tank it may be possible to put a second tank in next to it and interconnect them. It would decide on what space you have available in the attic.

shane0007

A closet tank is also a viable option when stuck for space. Everything including pump sits in the top of the unit.

http://www.platinum-tanks.ie/component/virtuemart/details/91/22/water-storage/attic-water-storage/closet-tank

JohnnieK

I have a main bathroom and ensuite and my 35kW viessmann combi works a treat. It's fed from the main tank in the attic via a booster pump. There seems to be more head of population in your house than mine so i would air on the side of caution about getting a combi, you should also think about upgrading your cylinder.

tea and coffee

Ok. How does this sound?
Option 1: 30kw condensing boiler with seperate zone for hot water only. New cylinder and poss. new cold water tank dependjng on size.
2 manual showers run off pump. Arsey fancy electric shower run off cold water tank with its own seperate pump ( or can i connect it to the other pump?)
Work needed:
-install boiler
-seperate piping from boiler for hot water only.
-new pump for manual showers as old one is ancient and remove old one
-new immersion tank
-pump for elec shower
-possible new cold water tank.

Option 2: Combi boiler run off cold water tank or mains ( seems plumber meant mains as he said pump to be in utility rm which is nowhere near water tank-or does it need to be near it?) With pump. 3 manual showers and gravity fed toilets.

Work needed:
- Install boiler
- install pump for boiler.
-remove immersion tank and old shower pump

Option 2 seems like less work (=less expense) but option 1 is the better job??

Outkast_IRE

I will always pick option number one.

As for electric shower find out what the mains pressure is and if its suitable just put a mira sport in , they are a perfect option for a backup shower.
If the mains pressure isn't enough then just get a tank fed one mira elite or similar.
They are a cheap option and are usually relatively easy to install .

tea and coffee

Think i will go option 1. The triton t90 is the sensible option but i really want this. http://www.tritonshowers.ie/triton-for-the-homeowner/triton-products/electric-showers/aspirante-riviera-sand.aspx which will need a pump. Possibly its own pump in fact. *blush*

tea and coffee

Talking to the plumber again today. He really favours the combi boiler. He says he will use a 35kw combi and a 3 bar pump off the attic water tank (which 30 + years old and only 60 gallon, so am relplacing it wither way). He will put the pump in the boiler house outside (at my request) and the boiler inside the utility room.
He insists no loss in pressure even if 2 showers going at once due to the pump. Instant hot water. No immersion tank and corresponding electricity charges from leaving it on.....I will have the tank with water in the attic same as anyone would if the mains gets cut off.


There doesn't seem to be any down side. (which worries me of course). I see what you are all saying in relation to the fact that they are not suitable for a larger property and the inter-webby is saying the same (Uk sites where they may not have a pump attached in fairness). The same sites also say there is a lag in how quickly the boiler can heat the water.

Also, if anyone had any idea which would be cheaper to run, that would be great.

I was fully convinced of the condensing after this thread, but he has me thinking again. Have I missed something? Is the 3 bar pump going to be enough to ensure we don't have wimpy showers? The noise aspect is taken care of...

:-/ Confused.com

rightjob!

the 3 bar pump will be fine..
id be more worried about having hot water when two showers are going at the same time

scudo2

tea and coffee wrote: »

Talking to the plumber again today. He really favours the combi boiler. He says he will use a 35kw combi and a 3 bar pump off the attic water tank (which 30 + years old and only 60 gallon, so am relplacing it wither way). He will put the pump in the boiler house outside (at my request) and the boiler inside the utility room.
He insists no loss in pressure even if 2 showers going at once due to the pump. Instant hot water. No immersion tank and corresponding electricity charges from leaving it on.....I will have the tank with water in the attic same as anyone would if the mains gets cut off.


There doesn't seem to be any down side. (which worries me of course). I see what you are all saying in relation to the fact that they are not suitable for a larger property and the inter-webby is saying the same (Uk sites where they may not have a pump attached in fairness). The same sites also say there is a lag in how quickly the boiler can heat the water.

Also, if anyone had any idea which would be cheaper to run, that would be great.

I was fully convinced of the condensing after this thread, but he has me thinking again. Have I missed something? Is the 3 bar pump going to be enough to ensure we don't have wimpy showers? The noise aspect is taken care of...

:-/ Confused.com

The problem with combination boilers is that the bigger draw off ie. the more/guicker the water passes through in the less chance it had to heat the tap water up to full tempature, that's the drawback. Fitting a 1000 bar pump wouldn't make it any better !
Pros and cons for everything in afraid.

ps. Good combination boilers are condensing also.
U Proberly ment condensing standard and condensing combination ( heat + taps)
"Grant" boiler is the make I recommend.

JohnnieK

You won't notice a major difference in performance with two showers running. I have had showers while the wife is running a bath for the kids and it hasn't effected the pressure or temperature enough to make me jump out of the shower in a rage.

Scudo is right there are pros and cons to everything.

The more important thing i will say is if the boiler is a bit away from the meter, the pipe will have to be increased to 1". There is no way you will get the full 35kW to the hot water if it is 3/4" or worse 1/2".

scudo2

JohnnieK wrote: »

You won't notice a major difference in performance with two showers running. I have had showers while the wife is running a bath for the kids and it hasn't effected the pressure or temperature enough to make me jump out of the shower in a rage.

Scudo is right there are pros and cons to everything.

The more important thing i will say is if the boiler is a bit away from the meter, the pipe will have to be increased to 1". There is no way you will get the full 35kW to the hot water if it is 3/4" or worse 1/2".

Showers are fine. Forget it if its the bath + showers. It all depends on the volume of hot water flowing that u need.
Its critical that the boiler is big enough for the job.

Mondeos (cars) are crap if they only have a 1.3 engine!! See what I mean.

Don't get me wrong, comby's are good.
Just back to pros and cons.

tea and coffee

Thanks. 35kw boiler with 3/4 inch pipes running as close to the showers as possible and then into regular 1/2 inch. Flow rate on the shower is 14.5L /min (thanks M.G- you know who you are).

JohnnieK

tea and coffee wrote: »

Thanks. 35kw boiler with 3/4 inch pipes running as close to the showers as possible and then into regular 1/2 inch. Flow rate on the shower is 14.5L /min (thanks M.G- you know who you are).

Sorry, i meant the gas pipe.

tea and coffee

JohnnieK wrote: »

Sorry, i meant the gas pipe.

Gas pipe will be 3/4 inch from meter to boiler to tank to pump to showers until they reach the shower and then reduce to 1/2 inch to fit the outlet on shower.
Boiler is from Ideal.

JohnnieK

Unless the meter is directly under the boiler or behind it some of that gas supply pipe is going to have to be 1" especially if it is a 35kW combi boiler.

tea and coffee

JohnnieK wrote: »

Unless the meter is directly under the boiler or behind it some of that gas supply pipe is going to have to be 1" especially if it is a 35kW combi boiler.

sorry my mistake 1 inch piep from meter to boiler

DGOBS

Seen a 35kw Vokera Mynute HE on a 1/2 pipe!!!!!! (from the hockey stick:eek:)

scudo2

DGOBS wrote: »

Seen a 35kw Vokera Mynute HE on a 1/2 pipe!!!!!! (from the hockey stick:eek:)

Who passed that?
How old and how many service eng. !!! Worked on it before an said its ok.

JohnnieK

DGOBS wrote: »

Seen a 35kw Vokera Mynute HE on a 1/2 pipe!!!!!! (from the hockey stick:eek:)

Its a good way of reducing the output :-D

mayd

May I butt in?
Installed Saturn 41B boiler 1 year ago
Not heating the water now - replaced the control box - heated the water initially but does not do so continuously - turning on shower but within two mins the water is cold.
Any ideas?

JohnnieK

mayd wrote: »

May I butt in?
Installed Saturn 41B boiler 1 year ago
Not heating the water now - replaced the control box - heated the water initially but does not do so continuously - turning on shower but within two mins the water is cold.
Any ideas?

Did you check out the plate to plate heat exchanger for any blockages?

mayd

JohnnieK
Thank you - service man found a faulty sensor - sometimes it heated but sometimes not, so a continuous supply of hot water did not generate !!
That was having spent 2 hrs going through all mechanics of the boiler - perseverance - a good guy.

Idbatterim

op make sure that pump only comes on for showers ideally!!! Are you putting in grey water system for loos etc?

jeepsterboy

my situation is different, but maybe simpler.

i'm not familiar with all the plumbing terminology, apologies, but was considering a combi OIL boiler rather than condensing. would appreciate any advice from plumbers or home owners with similar set-up.

my house is a small detached 2 bed bungalow (rural), with limited space for tanks downstairs. needing to install new system. i was looking at those internal combis that can be located in a kitchen....

it needs to service 7 rads in total
water pressure in area is very good
one bathroom (i don't want an electric shower)
i live on my own

if i was to go for a combi would it be fine?.... and would there be any advantages over a pressurised system (firebird out the back, tank in the attic)? many thanks.......