Trying to decide between 2 boilers

tooth*grinder

Howdy folks,
Getting the old (16year old) gas boiler replaced and after getting various quotes, the best price gives me the choice of a Glow worm FX as part of the original quote or a Worscester Bosch 18i with an extra 2 years guarantee for an extra €250.

Anyone got any experiences with either boiler? I've pretty much no idea what I'm talking about and a quick search turns up some 2 year old threads on glow worm issues (although nothing on the model I'm being quoted) whereas the Bosch returns nothing much other than where to buy them or the manufacturer's pages.
Is the glow worm sx ok or am I better off paying the extra €250?

Outkast_IRE

tooth*grinder wrote: »

Howdy folks,
Getting the old (16year old) gas boiler replaced and after getting various quotes, the best price gives me the choice of a Glow worm FX as part of the original quote or a Worscester Bosch 18i with an extra 2 years guarantee for an extra €250.

Anyone got any experiences with either boiler? I've pretty much no idea what I'm talking about and a quick search turns up some 2 year old threads on glow worm issues (although nothing on the model I'm being quoted) whereas the Bosch returns nothing much other than where to buy them or the manufacturer's pages.
Is the glow worm sx ok or am I better off paying the extra €250?

I have been working with the glowworms for years and have found them to be excellent and problem free.

Joey the lips

They are both good boilers. Sold them both at one stage. why an 18i... A plumber can correct me but is an 18i not an 18kw. Is your house a 2 bedroom

tooth*grinder

Cheers lads - I might have misread the bosch one as an 18i, it might be 181 - dunno if that's any better :-s
The place is a 3 bed, semi d, 2 storey.

JohnnieK

tooth*grinder wrote: »

Cheers lads - I might have misread the bosch one as an 18i, it might be 181 - dunno if that's any better :-s
The place is a 3 bed, semi d, 2 storey.

An 18i is plenty for your house.

Joey the lips

JohnnieK wrote: »

An 18i is plenty for your house.

Thank you johnnie. Can you tell me why? Am interested. Is it that 18kw is loads or does it modulate higher...

Its been so long i am just interested in a genuine sense

JohnnieK

Joey the lips wrote: »

JohnnieK wrote: »

An 18i is plenty for your house.

Thank you johnnie. Can you tell me why? Am interested. Is it that 18kw is loads or does it modulate higher...

Its been so long i am just interested in a genuine sense

It won't modulate any higher. A bog standard 3 bed semi would have normally a heat load of between 15 and 17kW. Infact my own house which would be a larger 3 bed semi has a 16kW boiler in it and is able to handle the 4 zones.

gdavis

a lot of factors determine that johnny?? windows,insulation etc.??

Joey the lips

I though all things being equal a standard 3 bed has a 24kw or 80 000 btus. I know it might never operate at that level but i was under the illusion that you 60 000 for heating and 20 000 for water.

Anyway... Your the plumber

With my boilers all 24kw are set at 16kw, in all the years i'v been here and the thousands of boilers sold, no installer or house holder has noticed the boilers are set at 16kw and very very rarely to I need to increase the output of a boiler.

JohnnieK

gdavis wrote: »

a lot of factors determine that johnny?? windows,insulation etc.??

Agree completely but with the houses that wher built 15 or so years ago, most would have double glazing and an ok standard of insulations. Using the building regs u values most come up with the figures stated.

Of course some come back that might be a bit over 18 and like with a rad you would go with the next size up.

tooth*grinder

Thanks for the info lads. The house is pretty warm even with the boiler that's been here for the past 16 years. Which, as far as we can tell hasn't been serviced. so based on that I'd reckon a brand new boiler with a newly flushed system should be grand at 18kw.
Or at least that's my hope!

tooth*grinder

tooth*grinder wrote: »

should be grand at 18kw.
Or at least that's my hope!

Boilers can have there output adjusted ie.. a 24kw boiler can be range rated between 5-24kw, so if you do have concerns a 24 can be adjusted to match the output of a 18kw, your installer should be able to identify your heat requirement and size the boiler accordingly, it's supposed to be maths not guesswork

Merch

I can see how it would be easier to calculate the kw demands for the hot water but the heating would be a bit more difficult,
each room would have to be done individually,

How do you determine the heat loss from an existing structure? of any material? without using standard figures, if you dont know how much or if any insulation is used?
how can you determine the losses? as each situation will be different.
Maybe in a new building where information is available on windows,doors,and the construction materials.

Joey the lips

Merch wrote: »

I can see how it would be easier to calculate the kw demands for the hot water but the heating would be a bit more difficult,
each room would have to be done individually,

How do you determine the heat loss from an existing structure? of any material? without using standard figures, if you dont know how much or if any insulation is used?
how can you determine the losses? as each situation will be different.
Maybe in a new building where information is available on windows,doors,and the construction materials.

Our principle for calculating was old with the figureing out that modern insulation can only improve. 200000 btus was allowed for hot water. Which again is vague i suppose especially as electric showers and washing machines that heat the water are so much the norm now.

Then you have the boiler industry. They can sell a boiler to you at the best price by mass production of 1 or 2 units so there aim is to make one size fit all. However with new condensing boilers the trick is to have them modulate a little more regular so a lower kilowatt setting makes sense I just wondered why 24kw was not the norm. Which my question has been asked.

However i am not questioning a plumber here so to speak but from memory i always remember a standard 3 bed with potterton/quinn rads use to come in about 40000 btus or 18kws so we would always spec a 24kw as it is the next size up and this was the supplier reccomendation. Additionally. If you got an extension like a conservatory or porch it allowed the extra rad to be fitted to the existing system.

Just to feed so info from our part.

Joey the lips

Joey the lips wrote: »

Then you have the boiler industry. They can sell a boiler to you at the best price by mass production of 1 or 2 units so there aim is to make one size fit all.

The rating on a boiler is only a indication of maximum output available and not what the boiler output is fixed at, it's always been the responsibility of the installer to do his calculations and then adjust the boiler to meet demand, Mears calculators and heat loss calculations have been around for a while.

greg_james

Hi i don't know why he's charging you €250 for an extra 2 years warranty on the bosch as the bosch system currently comes with a full 7 yr parts and labour warranty for all bosch installers also the glowworm comes with a full 5yr warranty for all RGI's, subject to an annual service. there isnt to much difference between them other than a small price difference in favour of the glowworm, bur worcester bosch have an unrivalled support service. as for the flue the glow has both rear and top arrangments, also the 24kw bosch is cheaper than the 18kw as it more popular. hope this helps

anuprising

gary71 wrote: »

With my boilers all 24kw are set at 16kw, in all the years i'v been here and the thousands of boilers sold, no installer or house holder has noticed the boilers are set at 16kw and very very rarely to I need to increase the output of a boiler.

would you not consider getting new installers ?:)

if the installers havent noticed that the output is down to 16 kw then they must not have commissioned it properly ,as this would show up when they gas rate the appliance ,would it not . the m3 would be significantly diferrent

Joey the lips

greg_james wrote: »

Hi i don't know why he's charging you €250 for an extra 2 years warranty on the bosch as the bosch system currently comes with a full 7 yr parts and labour warranty for all bosch installers also the glowworm comes with a full 5yr warranty for all RGI's, subject to an annual service. there isnt to much difference between them other than a small price difference in favour of the glowworm, bur worcester bosch have an unrivalled support service. as for the flue the glow has both rear and top arrangments, also the 24kw bosch is cheaper than the 18kw as it more popular. hope this helps

Interesting... You actually just supported my point.

Merch

Joey the lips wrote: »

Our principle for calculating was old with the figureing out that modern insulation can only improve. 200000 btus was allowed for hot water. Which again is vague i suppose especially as electric showers and washing machines that heat the water are so much the norm now.

Then you have the boiler industry. They can sell a boiler to you at the best price by mass production of 1 or 2 units so there aim is to make one size fit all. However with new condensing boilers the trick is to have them modulate a little more regular so a lower kilowatt setting makes sense I just wondered why 24kw was not the norm. Which my question has been asked.

However i am not questioning a plumber here so to speak but from memory i always remember a standard 3 bed with potterton/quinn rads use to come in about 40000 btus or 18kws so we would always spec a 24kw as it is the next size up and this was the supplier reccomendation. Additionally. If you got an extension like a conservatory or porch it allowed the extra rad to be fitted to the existing system.

Just to feed so info from our part.

I'd have to convert from Btu's to kW's, not too familiar with that
I was basing a calculation on the Cp of water x the time required x the volume in litres, I'd need to confirm that but I was getting a result of 2.5kW using 160 litres in an hour or only 8000btu's 200000 seems like a lot?
I'll have to go over my own calculation as its figures off the top of my head (and calc in windows) so im not saying you're wrong as not as familiar with btu's, just seems a lot for a domestic house??

I'm just doing it partly as a matter of interest/curiosity, too much to do it right now, but I plan to do a room by room calculation just to see what figures I come up with and to see how much insulation of different sizes might improve that and trade the cost of that against the cost of improvements
As I dont know what certain aspects of the construction are e.g. the floor, I will have to estimate a lot of it. I'm sure there are set figures for heat transmission for certain materials e.g. a cavity block, an air space or a standard plasterboard wall?, maybe its in the building regs? if anyone can confirm great, if not I'll pore over each page eventually, thats when im done with all the jobs at hand.
I'll probably do it in excel so i can adapt and change it.

what are peoples opinions on minimising capacity of the boiler as it never usually needs to meet maximum demand all the time, it will therefore cycle on and off more meaning it will be more inefficient.

Joey the lips

Sorry there is an extra 0 in mine it was ment to be 20,000 btus for water.

Merch

Merch wrote: »

what are peoples opinions on minimising capacity of the boiler as it never usually needs to meet maximum demand all the time, it will therefore cycle on and off more meaning it will be more inefficient.

Oversizeing a boiler is like trying to get a elephant in to a rabbit hutch.

You don't minimise capacity, you find out your heat requirement and adjust the boiler output to meet this.

Merch

gary71 wrote: »

Oversizeing a boiler is like trying to get a elephant in to a rabbit hutch.

You don't minimise capacity, you find out your heat requirement and adjust the boiler output to meet this.

I mean I think oversized is bad, bad for efficiency, cycling etc
what Im saying is given that the heat requirement for space and hot water are not always required at the same time, calculating for the max possible eventuality for space heating and hot water means the boiler will be oversized for what is needed most of the time except in extreme temp lows where you want hot water too.

having a lower capacity boiler means runs longer but more efficiently, than say a larger boiler that turns on and off, no?
I cant understand why there isnt a boiler that has a variable capacity, I can understand if its a fixed setting, like a nozzle or pressure adjustment. but with modern (internal controls) surely its possible to switch between a high medium and low setting, dependant on the internal temperature needed and external temp that exists.

You're not oversizing a boiler if you match it to the heat load required, your just designing a system to work correctly.

What your looking for can be achieved with proper heating controls, modern gas boilers have modulating pumps as well as modulating heat output to reduce cycling, also you can fit boilers that allow you to send a high temperture to the cylinder for quick reheat and a lower to the rads to improve the chances of the boiler condensing, chuck in a outdoor sensor then happy days, your installer should be advising you as he has seen your installation.

Merch

gary71 wrote: »

You're not oversizing a boiler if you match it to the heat load required, your just designing a system to work correctly.

What your looking for can be achieved with proper heating controls, modern gas boilers have modulating pumps as well as modulating heat output to reduce cycling, also you can fit boilers that allow you to send a high temperture to the cylinder for quick reheat and a lower to the rads to improve the chances of the boiler condensing, chuck in a outdoor sensor then happy days, your installer should be advising you as he has seen your installation.

A modulating boiler? so the output can be varied dependent on conditions or requirements? I was told previously such a thing is not possible/available, if it is can you name the boiler makes and models capable/that you are aware of.
I'm not replacing it just now, but when I am my concern will be wanting to get what you have described for my home and an installer able to do that.
I've read a bit here (and only here) but I've seen it mentioned regarding approved installers for certain makes, so I'd presume such approval means the installer would be familiar with all aspects for the specific makes they cover.
Makes that have been mentioned, Ariston, Bosch, Worcester, Veissmann.

Modern gas boilers can do a lot of clever things, Viessmann have a boiler with two flow pipes, one for hot water and one for heating, allowing two different circuits with different temperatures, another manufacture allows the heating circuit to run at a temperture influenced by a outdoor sensor i.e. 52c and then ignore the outdoor sensor and increase to a higher flow temperture i.e. 65c when the hot water circuit calls for heat.

Gas boilers have always modulated there is nothing new in that, it's more of a system design issue than a boiler issue if a boiler is cycling.

One thing about system design here I wouldn't be a fan of is a balancing valve slowing the circulation around the hot water circuit, I prefer the coil on a cylinder to get all the heat it can take to have the fastest possible reheat time.

Merch

gary71 wrote: »

Modern gas boilers can do a lot of clever things, Viessmann have a boiler with two flow pipes, one for hot water and one for heating, allowing two different circuits with different temperatures, another manufacture allows the heating circuit to run at a temperture influenced by a outdoor sensor i.e. 52c and then ignore the outdoor sensor and increase to a higher flow temperture i.e. 65c when the hot water circuit calls for heat.

Gas boilers have always modulated there is nothing new in that, it's more of a system design issue than a boiler issue if a boiler is cycling.

One thing about system design here I wouldn't be a fan of is a balancing valve slowing the circulation around the hot water circuit, I prefer the coil on a cylinder to get all the heat it can take to have the fastest possible reheat time.

I was thinking of that in both rads and on hot water tank. I think that it is just because it is a fixed setting on some setups, but with an electrically operated valve, you could surely have full flow on the hot water when you want and then full on the space heating circuit, but what about when both are in use?? I suppose once the demanded hot water is reached it can shut off?? if you can prioritise one or the other though, say if it was more essential to heat the spaces than the water first that would be good.
It seems odd to me to restrict the flow on the space heating too, from what I gather the rad balance valves are closed down to restrict flow, if anything I was thinking that the valves (balancing) should be opened up fully and only closed the necessary amount to restrict flow to ensure even distribution of heat,
but
doesnt a thermostatic valve do that essentially anyway
Restricting the flow in the rads must create a back pressure that restricts the pump by increasing the load on it, making it operate harder/use more power to achieve the same work. I guess thats where automatic variable speed pumps come in??

The issues you describe can be delt with in decent system design and a good auto bypass on a system helps a lot, balancing the rad side of things is very important.

Modern cylinders have improved coils on them which give quicker reheat times, I'm used to heating system that do not have balancing valves on the cylinder and they work very well, the cylinder may rob heat from the heating circuit but that's only till the cylinder reaches temperature(as you posted;)).

cikearney

Viessmann boilers are leading the way across europe and offer a 20 year gaurantee on there heat exchanger, and if fitted by a viessmann trained professional offer a 5 year parts and labour gaurantee
And are moderatley priced @ about €1300inc ex trade

Merch

When getting a new boiler fitted do most approved installers (I assume RGI, I mean company approved/trained by manufacturer) do a flush of the system?
It's probably likely by the time I'd get this done that I'd replace the hot water tank as its just got the lagging on it that I put on.
I may consider the options of a tank that can be connected to solar thermal (pressurised?) at a later date or a standard one like I have but with a few centimeters of foam moulded over the surface.

I have read recently on another thread on boards about someone getting repairs on tanks due to corrosion and it made me consider how to prolong the life of an existing or even new tank. There was talk of a sacrificial anode being placed in the tank? I am aware sacrificial anodes are used in other industry's, usually bolted in contact to the material you want to protect.
Is it a block of material anodic to the copper/iron in a heating system, thats dropped into the tank before sealing it up? how long do they last? as they obviously deteriorate over time. Thsi must get into the hot water thats used?
As I have noticed over time that my CH system seems to have the minimum of effort put into installing drains/shut off valves that are visible (maybe to save cost?), it makes me wonder when it comes to things that aren't visible if such a thing was ever dropped into my tank?

I'd more or less assumed the copper was resistant to corrosion and it was the iron in the rads and boiler that were subject to the worst deterioration, as after a good few years its that part I've replaced (rads).

JohnnieK

10 years on the heat exchanger as far as i know, unless that's changed in the last week. The 100's also have a 5 year warranty as standard now regardless of the installer. Still it's a good day out in Telford for the training.