Two smaller combies instead of a larger one?

[countmore]

Hi
Would like to ask your opinion on an idea (as stupid as it might sound).

I have 4 bedrooms, one bathroom with shower above, and extra shower room suite. I have been looking in many different direction to come up with a good idea to feed the whole house with heating as well as powerful showers.
A 30kw or higher combi seems not adequate to run both showers at the same time.
Unvented system will cost me over £3600+ (including a new boiler)
Normal vented system will leave me having to install a noisy pump+ a new tank as well as boiler
I have looked at thermal storage, heat bank etc etc etc
Even read about Atmos multi

So i was thinking of this idea
Two smaller combies in the airing cupboard. Each feeding a separate bathroom. One combi to heat downstairs rads and the other to heat upstairs rads. Effectively creating two zones to save on heating bills.
I figured the costs of labour won't be much more than putting a single one in and each combi will only be used half as much. No need to have downstairs rads on when you are sleeping at night or vice versa.

So what do you think?
I am more then ready to be the object of a bit of humor to all you experts out there. So go ahead and tell me how stupid this sounds but also give me the pros and cons as well.
Many thanks
Sean
PS: I am a General decorator by trade and not a plumber

 

[Tibbot]

I apologise, if in the unlikely event this post is genuine. However it reads like another Drivel/Water Systems etc. attempt at posting to himself.

 

[countmore]

I apologise, if in the unlikely event this post is genuine. However it reads like another Drivel/Water Systems etc. attempt at posting to himself.

Lol, that is OK. As i said i did expect remarks coming in.
I am no expert but i am the kind of person who will not just call in a plumber and accept what he says. I have had plumber who suggested a 24kw combi without even looking at how many rads i had. When i questioned him, he simply said "oh, if you are not happy, I'll put in a 30kw then". It was at that point that i decided i would have to come up with my own idea and get it right before i go back to a plumber.
I have been at this for 3 weeks now searching and trying to come up with the best system with lowest costs.
I wouldn't need to ask if i really thought this was the way forward, but not being an expert and having seen some of the remarks made by others regarding novices then i put in a disclaimer in my post.

So will you now offer me the pros and cons please. If you know.
Many thanks.

 

[mickyg]

i think you underestimate the cost and possible difficulties in installing 2 combi boilers. A heat only boiler, UV cylinder and sealed system kit would be my prefference, assuming your mains cold water can deliver adequate flow for the Unvented. The cost to repair modern combis is becoming extortionate and there's alot to be said for using as few manufacturer specific components as possible.

 

[countmore]

i think you underestimate the cost and possible difficulties in installing 2 combi boilers. A heat only boiler, UV cylinder and sealed system kit would be my prefference, assuming your mains cold water can deliver adequate flow for the Unvented. The cost to repair modern combis is becoming extortionate and there's alot to be said for using as few manufacturer specific components as possible.

Could you please advice me. Since UV system would be the best way forward then would a combi boiler with storage tank inside would do the same job? Perhaps this way i might save on space by having a tank inside the boiler.
If as you have said a heat only boiler will cost less to maintain, then how about the cost of repairs to unvented cylinder?
Many thanks

 

[mickyg]

Yes a store combi would offer an "all in one" solution, but you will be at the mercy of the manufacturers for repairs and spares !
A good quality heat only boiler will very rarely fail, a decent brand UV will probably never fail at least inside the first 10yrs or so, there's really very little to go wrong with them.

 

[countmore]

Yes a store combi would offer an "all in one" solution, but you will be at the mercy of the manufacturers for repairs and spares !
A good quality heat only boiler will very rarely fail, a decent brand UV will probably never fail at least inside the first 10yrs or so, there's really very little to go wrong with them.

Thank you for very informative info. Just one last question.
What size UN tank will i need to supply hot water to two showers and heating. We hardly ever use the bath.
I asume a 24kw boiler should be enough. I have 11 rads around the house, some large (double) and some single.
At least i now know what i want before i go to a plumber. My experience has proven that they all offer to put in a combi first.
many thanks

 

[Agile]

You need to calculate the heat loss of the boilding first and then add 2 kW for the unvented but most programs include the allowance for the hot water. Probably about 18 kW.

However, there is nothing you can do until you have measured the dynamic flow rate out of the mains.

The storage combi will only delived about 20 li/min for about 10 minutes before it reverts to the underlying 14 li/min.

Whats more important is how many people you have living there and when they want to shower.

I would always recommend the unvented as that has electric backup and the boiler is cheaper and simpler.

My opinion is that you have ovestimated the cost of an unvented system.

Tony

 

[GeorgeBainbridge]

Hi
Would like to ask your opinion on an idea (as stupid as it might sound).

I have 4 bedrooms, one bathroom with shower above, and extra shower room suite. I have been looking in many different direction to come up with a good idea to feed the whole house with heating as well as powerful showers.
A 30kw or higher combi seems not adequate to run both showers at the same time.

ATAG make a 51kW combi that will clearly do two showers at one time. The Avantaplus 39C will also do two.

So i was thinking of this idea
Two smaller combies in the airing cupboard. Each feeding a separate bathroom. One combi to heat downstairs rads and the other to heat upstairs rads. Effectively creating two zones to save on heating bills.

Good idea.

I figured the costs of labour won't be much more than putting a single one in and each combi will only be used half as much. No need to have downstairs rads on when you are sleeping at night or vice versa.

Spot on.

So what do you think?
I am more then ready to be the object of a bit of humor to all you experts out there. So go ahead and tell me how stupid this sounds but also give me the pros and cons as well.
Many thanks
Sean
PS: I am a General decorator by trade and not a plumber

A good idea. The benefits are as you stated,

1. simplicity of installation.
2. They just need a clock/stat each - could be wireless
3. No electric control wiring.
4. Cheap to do. Two combis can be got cheaply.
5. Quick to install, so less labour, so cheaper.
6. CH zoned naturally, so cheap to run
7. Combis used less as load is split.
8. Showers not influenced by each other.
9. Can deliver 25 litres/min for ever.
10. Join both DHW outlets using two check valves and a small shock arrestor to fill only the bath.
11. Back up DHW and CH if one is down
12. Takes up less space than a cylinder.
13. Very fast warm up in the morning as 60-62kW is being used to heat the house.
14. Cheap to run as there are no cylinder standing heat losses.
15. Many combis condense on DHW as well so further cheaper to run.

The only down side is two service costs per ann. You will get a discount having two together. Unvented cylinders need an annual service as well, and bubble reinstating, large discharge pipes to outside,being ugly and sucking heat out of the house and all that. No G3 to fix them like an unvented cylinder. No expensive to replace pressure controls like on the unvented cylinders. Explosion risk far, far less.

A good idea. Go for it! Price it up.

 

[GeorgeBainbridge]

i think you underestimate the cost and possible difficulties in installing 2 combi boilers.

How can you say that? The cost is cheap. Two combis is cheap. Price them up. The only extras, apart from pipe and rads, which you need anyhow in any system, is two programmer/stats. What difficulties? It is simple. No control wiring, cylinder, 3-way zone valves and all that. Just one wire from each combi to a programmer/stat. Full independent CH control on two floors.

They will fill a bath very quick. Two combis is common on the Continent in two bathroom houses.

 

[Agile]

How can you say that George when you have never installed any boilers?

There are clearly TWO boilers to install and so the cost will be virtually double the cost of installing one.

If a very large 50 kW combi is fitted then the minimum heat output is likely to be at least 15 kW and the boiler will have no modulation range available for heating and will be forced to do inefficient on/off modulation.

Unlike an unvented, if a single large combi fails then you have no heating or hot water until its fixed.

Tony

 

[GeorgeBainbridge]

There are clearly TWO boilers to install and so the cost will be virtually double the cost of installing one.

If a very large 50 kW combi is fitted then the minimum heat output is likely to be at least 15 kW and the boiler will have no modulation range available for heating and will be forced to do inefficient on/off modulation.

Tony

As countmore wrote, the installation of two is easy as they are next to each other.

This one writes drivel with no experience of what he is writing. He should find out before writing. The ATAG Q51C modulates from 8.8 - 44.7kW.

Unlike an unvented, if a single large combi fails then you have no heating or hot water until its fixed.

If a boiler fails with an unvented cylinder you have no heating at all. You can only have DHW backup with an immersion heater. A thermal store can have electric backup to CH and DHW. With a combi a small backup in-line electric water heater can be fitted, if backup is a big problem. They give enough hot water for a day or so. Countmore is asking about two combis which give CH and DHW backup in the house. Take notice of us professionals.

 

[PEDANTICVINDICTIVEMAN]

Going to have to have enough decent mains coming in to run both combi's at the same time, also a LARGE gas pipe ( how far away is the meter) to supply both combi's, also need to check the gas meter will pass say 2 x 30Kw = 60kw = 5.61 m3/hr, doesn't leave much for cooking and gas fires in NG.

 

[mickyg]

i think you underestimate the cost and possible difficulties in installing 2 combi boilers.

How can you say that?

Because unlike you I actually work in this industry. I actually go to peoples houses and price up work. I know what things cost, and how difficult/easy some particular jobs might be, when to the untrained eye it seems all so simple. I've carried out jobs with 2 or even 3 boilers in one property, I've installed unvented cylinders, thermal stores, combis and pretty much everything else that can go in a domestic home. YOU have done nothing, but sit on a computer, googling for products then pretending you know something about them, other than whats written in the brochure. I can only assume you do it to wind people up, because certainly no one is going to take you seriously. Carry on with the insults though, I'm sure another ban is just around the corner.

 

[GeorgeBainbridge]

Going to have to have enough decent mains coming in to run both combi's at the same time, also a LARGE gas pipe ( how far away is the meter) to supply both combi's, also need to check the gas meter will pass say 2 x 30Kw = 60kw = 5.61 m3/hr, doesn't leave much for cooking and gas fires in NG.

True the gas supply has to be looked at on the outlet side of the meter. But if the two are next to each other not a great task. Two 24kW combis will give enough meter capacity for a hob as well. Both will give a decent shower and when the DHW outlets are combined for a bath only, will fill the bath up fast.