Combi Boliers... what's the story

fillup

Hi
i'm getting work done on my house and as part of the work im replacing and moving my boiler.
i've heard about combi boilers that remove the need for a cylinder/hotpress
can some explain in lay mans terms the pros and cons of these systems.
one thing i know is that they are dependent on your water pressure, how do i measure my water pressure, i'd say its below average but how can i tell???
thanks in advance

Stratocaster

fillup wrote: »

Hi
i'm getting work done on my house and as part of the work im replacing and moving my boiler.
i've heard about combi boilers that remove the need for a cylinder/hotpress
can some explain in lay mans terms the pros and cons of these systems.
one thing i know is that they are dependent on your water pressure, how do i measure my water pressure, i'd say its below average but how can i tell???
thanks in advance

This type of boiler is big in the UK but not as common here. They are ideal for use in offices and work type buildings as you can have instant hot water. It all depends on your hot water demand. If you have a lot of bathrooms in use a combi boiler is expensive to run. A combi boiler has two heat exchangers and the primary heat exchanger is for your hot water. If your running your boiler for heating and start to draw off hot water your heating side of the boiler will suffer. Again depending on the size of your house its not a good idea to have a combi when you have x amount of radiators.

Since your replacing your boiler additional plumbing pipe work will be required so you have to consider the extra labor costs. Storing hot water in a cylinder is good for the finances, it doesn't really cost that much extra to keep your cylinder hot while the boilers on heating the rads. To remove a cylinder from a house is not a good call. The most important factor to consider is you will have no backup. If your boiler breaks down and it will. You wont have any hot water. With a cylinder you can resort to the immersion.

For water pressure as with most boilers it will probably require min of 1 bar. Co councils only allow mains water to be fed to your kitchen sink and your attic tank your not allowed to take any other feeds off the water main. You have to consider where to get a pressurized supply to the combi to feed your hot water outlets. There is a lot more to installing a combi than just swapping over from an existing boiler.

The idea behind a combi was to give apartments with a lack of space a means of heating and hot water, i would never replace stored hot water with a combi unless there was a good reason for it IE... to free up space(main reason) or to take advantage of powerful mains, the reasons i would keep the cylinder would be that most combi's i work on aren't fitted properly even though they are easier to install from new than a system boiler, also as Stratocasteras wrote the lack of hot water back up(unless you fit a electric shower), they are more complex inside than system boilers, they don't work well with multi bathroom properties and they *must* have good incoming mains pressure, ask your installer what you have in liters per minute and compare it to the requirements of the boiler you like, some installers will get by the lack of pressure by fitting a break tank and pump, but i can count on one hand how many break tanks were big enough to do the job and there are dodgy fellas that will stick a pump on the mains, the gas supply is another big problem as installers tend to go for the largest boiler output possible to give good hot water performance without sizing the gas pipe properly which can starve the boiler when it fires for hot water, but to be fair combis have there uses as well if fitted properly, if you have the mains they will give you plenty of hot water without ever running out, good showers and space saving, have less pipe work than system boilers(new installation). In respect of the impact using hot water will have on the heating, i have lived in 3 houses with combis and have never noticed a problem also i have never had a complaint from a customer because of it, i find people adapt to it in the same way you would using a cylinder, Gary.

Stratocaster

Stratocaster wrote: »

primary heat exchanger is for your hot water.

Secondary/plate heat exchanger for hot water, Christ I've become a boiler nerd:eek:

fillup

thanks for the info lads...but i'm still a bit confused,, lets see if i;ve got this right:
1 there a good idea if you want to save space (whilst we have space for a hot press we were thinking that if we could get rid of it we could put the space to better use)

2 they're easier to install, if the installer knows what's he's doing

3 you have no back up if they fail...

with that in mind i have 2 more questions

i will be running 1 bathroom and downstairs loo, (1 shower and 2 hand basins) and a kitchen off it from a hot waterside and about 10 rads from a heating perspective.. is this feasible???

are they more economical than other boilers???

cheers

Stratocaster

Gary I take it you come from a plumbing background. Unless the rules have changed here without someone telling me. You can only take two connections off a Co Council mains water supply. One for drinking water at the kitchen sink and a second for cold water storage. That's it. By making anymore connections the Co Council has the right to disconnect your water supply. Due to to poor regulation on plumbing here the above is not the case.

The only time you will have an issue with the Co Council is if you apply for a new water main. A Co Council rep will view the installation, sometimes same day as making the connection from the road. I've witnessed this, some will let things slip and others wont, it depends on how you treat the rep but I wont go into it.

In Ireland to my knowledge the only way the original poster can install a combination boiler is by the use of a break tank. Its not allowed to be feed directly from the mains supply.

Stratocaster

gary71 wrote: »

Secondary/plate heat exchanger for hot water, Christ I've become a boiler nerd:eek:

Not on the last combination I installed. It was designed for primary hot water use. Just taking the worst case scenario.

Stratocaster

fillup wrote: »

thanks for the info lads...but i'm still a bit confused,, lets see if i;ve got this right:
1 there a good idea if you want to save space (whilst we have space for a hot press we were thinking that if we could get rid of it we could put the space to better use)

2 they're easier to install, if the installer knows what's he's doing

3 you have no back up if they fail...

with that in mind i have 2 more questions

i will be running 1 bathroom and downstairs loo, (1 shower and 2 hand basins) and a kitchen off it from a hot waterside and about 10 rads from a heating perspective.. is this feasible???

are they more economical than other boilers???

cheers

I don't think a combi will be beneficial for your installation. You can purchase a more economical boiler.

Energy efficient condensate gas boiler. Some can go up to 91% efficient.

Forgot to mention you may even be able to apply for a government assistance grant for the new boiler, not fully sure. Its worth looking into.

No, i am not a plumber(i don't do toilets:D), I'm a gas fitter by trade and now i work for a boiler manufacturer specializing in identifying installation faults or boiler faults on new installations, you are correct in the point you make, but there are so many fruit loops fitting boilers incorrectly filling loops are ignored by the powers that be, i think the issue with pumping the mains is the biggest problem, then followed by small break tanks(which is not a water reg issue), as for filling systems from the mains if fitted as per manufactures instruction it's not a problem, it's how most council's are now fitting boilers and i cover all of Ireland and the North, i have worked here a few years now and the things installers get away with is mind blowing and i have yet to see a water reg in forced, Gary.

Stratocaster

gary71 wrote: »

No, i am not a plumber(i don't do toilets:D), I'm a gas fitter by trade and now i work for a boiler manufacturer specializing in identifying installation faults or boiler faults on new installations, you are correct in the point you make, but there are so many fruit loops fitting boilers incorrectly filling loops are ignored by the powers that be, i think the issue with pumping the mains is the biggest problem, then followed by small break tanks(which is not a water reg issue), as for filling systems from the mains if fitted as per manufactures instruction it's not a problem, it how most council are now fitting boilers and i cover all of Ireland and the North, i have worked here a few years now and the things installers get away with is mind blowing and i have yet to see a water reg in forced, Gary.

Great I hear you now. I have been involved with the plumbing and heating industry here for over 10 years and will continue to give advice on what I been thought and the regulations I been advised on. I have yet to un cover today's modern mains water regulations as with each Co Council there seems to be a difference in whats acceptable and whats not.

You right the standard of installations is atrocious and I will greet the day when water rates are introduced. By introducing a water rate the standards of installations will become an important factor. You will see strict regulations enforced and by doing this the un qualified bad practice installers will be weeded out. These guys are only in business because they can offer cheap bad quality installation quotes more attractive than those who plumb by the rules. The initial cost of water will upset people but I believe savings will be made as systems will be installed correctly with less maintenance costs occurred and peace of mind is priceless.

fillup

fillup wrote: »

thanks for the info lads...but i'm still a bit confused,, lets see if i;ve got this right:
1 there a good idea if you want to save space (whilst we have space for a hot press we were thinking that if we could get rid of it we could put the space to better use)

2 they're easier to install, if the installer knows what's he's doing

you have to take into account the pipework you're removing and running the flow and return back to the correct position and repositioning gas supply, mains and hot, bread and butter to a proper plumber nightmare for a fruit loop

fillup wrote: »

3 you have no back up if they fail...

with out a electric shower you will be boiling the kettle and having a flannel down till the boiler is fixed

fillup wrote: »

with that in mind i have 2 more questions

i will be running 1 bathroom and downstairs loo, (1 shower and 2 hand basins) and a kitchen off it from a hot waterside and about 10 rads from a heating perspective.. is this feasible???

With good mains, decent plumbing and the right boiler you will not have a problem, combis have different characteristics to system boilers and once you get use to it it not a problem,

fillup wrote: »

are they more economical than other boilers???

It's all relative to how it's fitted and what controls you use what ever type of boiler you go for, If you look at the Sedbuk list http://www.sedbuk.com/ you will see the efficiency's of different boilers, remember to take off 4-5% as condensing boilers don't condense all the time, as for the running cost of a combi to a system boiler personally i think combis are more precise as you are only heating the water you use, but if the hot pipe loops halfway round your house you could be wasting money and water so as i said it's all relative. My knowledge is mainly gas based i don't know enough about oil to comment on there efficiency, Gary.

Stratocaster

Stratocaster wrote: »

Not on the last combination I installed. It was designed for primary hot water use. Just taking the worst case scenario.

Every day is a learning day;), but I'm still a boiler nerd, and as for the quality of installations in Ireland as a competent gas engineer i am shocked at the things i see on a weekly basis for gas boilers and unvented cylinders, Gary.

Carlow52

Interesting and informative thread thus far:

One area where combi boilers work well is with solar thermal heating installations where u have a large heat storage tank. Some combi boiler manufacturers have an upper limit on the input water temp but the combi boiler covers off the legionnaires disease issue.

Having read the thread, is actual boiler downtime such an issue to require immersion backup?

Carlow52

Carlow52 wrote: »

Having read the thread, is actual boiler downtime such an issue to require immersion backup?

Depends on the quality of engineer standing in front of the boiler, the information available on the product, the availability of parts and how cold it is outside, if you have a top end boiler no problem, if you have a heatline your in trouble, Gary

Stratocaster

Carlow52 wrote: »

Interesting and informative thread thus far:

One area where combi boilers work well is with solar thermal heating installations where u have a large heat storage tank. Some combi boiler manufacturers have an upper limit on the input water temp but the combi boiler covers off the legionnaires disease issue.

Having read the thread, is actual boiler downtime such an issue to require immersion backup?

Its an issue if your like most people in Ireland who will only call for a boiler service when the boiler stops working. A boiler should be serviced at least once a year. If you keep your boiler serviced regularly it will minimize your downtime. But there will be some downtimes during a boilers life. The duration of the downtime is dependent on what Gary is saying.

You have to consider a downtime in the worst scenario in all installations so the issue is depending on the instillation.

A B&B cant afford to have a downtime. There must be a back up in this installation.