Combi boiler - which ones if any?

[agmz4]

I have a five bedroom two bathroom house. The boiler is conventional with a storage tank (i.e. gravity feed) and this supplies the central heating and hot water. We have showers over the baths and the force is very low.
I have consulted two plumbers/heating engineers and one swears that replacing our existing boiler andd tank with a combi would do the trick and other says the house is too large and we should go for a pumped system or go for a megaflow system. The latter system is unattractive due to the size of the installation. I have been reading up about combi boilers and there seem to be about four basic types. Can anyone suggest a make and model which would be powerful enough to service two bathrooms and improve the flow rate.

Many thanks,

AGMZ4

 

[gas4you]

Have either of them tested your mains pressure and flow rate?

Without these basic tests done first they could both be wasting your time and money

 

[BigBurner]

Wall mounted:

Mikrofill Ethos 54 kw (very small case)
Vaillant 937 (very big on wall)
Alpha CD50
Glow Worm Extramax
Eco-Hometec

Floor mounted:

ACV Heatmaster
Atmos Multi
Worcester-Bosch High Flow 440 (washing machine sized)
Vaillant 333
Glow Worm Ultrapower
Gledhill Gulfstream, (can do 3 baths)
Potterton Powermax

All decent makes (The Pott is dicky) and take your pick. Make sure you have a 22mm cold feed pipe from combi to the cold maintap.

Look at a Rinnai or Andrews multi-point and separate small CH boiler.

The great thing about instant water heaters is that you can stay in the shower for ever. An instant water heater or combi can deliver 20 litres per minute for 30 minutes. That is 600 litres. How much would a 600 litre unvented cylinder cost? No contest. Instant water heating is great for body jet showers.

 

[ChrisR]

All sounds advice I'd say. If you had a good enough mains supply, and a largeish unvented cylinder, you can take les extravagant showers more or less one after the other as long as there's a normal body-drying gap between.
Can do precise sums if you like but you get the idea.

All hinges on mains pressure (and flow). If you like a shower to feel invigorating you need pressure, flow alone won't do. That may mean you have to store water and use a pump. Bucket of water over your head is a lot of flow, but not very exciting!

 

[BigBurner]

All sounds advice I'd say. If you had a good enough mains supply, and a largeish unvented cylinder, you can take les extravagant showers more or less one after the other as long as there's a normal body-drying gap between.
Can do precise sums if you like but you get the idea.

Body jet showers are now becoming the standard. Only instant hot water heating can cope with them. Main pressure and flow is the case in any mains fed system. If that is not up to it then you have problems.

The sums? Delivering enough flow for a body jet shower or two, only instant water heating wins in cost. High flow combis win in cost vs a system boiler and any cylinder any day.

 

[Nixt]

OP- Your choice may be affected on how dependent on gas you wish to be for a large property. There are solar modules available for some combi's but performance claims so far are dubious. By planning a store of hot water, whether a domestic a cylinder (with solar-coil) or primary water in a thermal store (with multi-coil) means you can utilise other heating support methods available.

 

[agmz4]

Have either of them tested your mains pressure and flow rate?

Without these basic tests done first they could both be wasting your time and money

Pressure is 2.5 bar before the kitchen tap is on. After it is on 2 bar working pressure. Flow rate 8l/min.

Many thanks,

AGMZ4

 

[agmz4]

Wall mounted:

Mikrofill Ethos 54 kw (very small case)
Vaillant 937 (very big on wall)
Alpha CD50
Glow Worm Extramax
Eco-Hometec

Floor mounted:

ACV Heatmaster
Atmos Multi
Worcester-Bosch High Flow 440 (washing machine sized)
Vaillant 333
Glow Worm Ultrapower
Gledhill Gulfstream, (can do 3 baths)
Potterton Powermax

All decent makes (The Pott is dicky) and take your pick. Make sure you have a 22mm cold feed pipe from combi to the cold maintap.

Look at a Rinnai or Andrews multi-point and separate small CH boiler.

The great thing about instant water heaters is that you can stay in the shower for ever. An instant water heater or combi can deliver 20 litres per minute for 30 minutes. That is 600 litres. How much would a 600 litre unvented cylinder cost? No contest. Instant water heating is great for body jet showers.

Many thanks - how do you feel about combined primary storage units?

AGMZ4

 

[gas4you]

With only 8 l/m you are wasting your time and money

Unvented such as a megaflo ideally needs at least 20 l/min and 3 bar, whilst any large storage combi will need the same.

 

[simond]

Using the figures you have supplied, you can have an unvented or a hi flow combi if you invest in an accumulator.

You could also try replacing the water main but this doesn't come with any guaranteed results, or, as some other wag on here likes to point out somewhat patronisingly, you could check your stopcock is fully open.

Otherwise you are wasting your time with a mains pressure device. Stick to a cistern fed (gravity) system.

 

[agmz4]

With only 8 l/m you are wasting your time and money

Unvented such as a megaflo ideally needs at least 20 l/min and 3 bar, whilst any large storage combi will need the same.

Many thanks - agmz4

 

[BigBurner]

Wall mounted:

Mikrofill Ethos 54 kw (very small case)
Vaillant 937 (very big on wall)
Alpha CD50
Glow Worm Extramax
Eco-Hometec

Floor mounted:

ACV Heatmaster
Atmos Multi
Worcester-Bosch High Flow 440 (washing machine sized)
Vaillant 333
Glow Worm Ultrapower
Gledhill Gulfstream, (can do 3 baths)
Potterton Powermax

All decent makes (The Pott is dicky) and take your pick. Make sure you have a 22mm cold feed pipe from combi to the cold maintap.

Look at a Rinnai or Andrews multi-point and separate small CH boiler.

The great thing about instant water heaters is that you can stay in the shower for ever. An instant water heater or combi can deliver 20 litres per minute for 30 minutes. That is 600 litres. How much would a 600 litre unvented cylinder cost? No contest. Instant water heating is great for body jet showers.

Many thanks - how do you feel about combined primary storage units?

AGMZ4

A CPSU is a combined thermal store that does DHW & CH off the store, with a boiler all in one case. The W-B HighFlow has a thermal store but only does DHW off the store, so is a stored water combi. I think the Gledhill and ACV HeatMaster are about the only ones left. The ACV is very good.

At 8 litres/min you are in big trouble. If the mains cannot be updated then go for an accumulator and a quality high flow combi. The most cost effective route. Anything else will be mega money.

 

[ChrisR]

At 8 litres/min you are in big trouble.

He said 8 l/min with 2 bar wp.

OP - You need to find what your max flow is.

Body jet showers are now becoming the standard.

Who said anything about Body jet showers?

Only instant hot water heating can cope with them

Shower towers with multiple heads aren't particularly high flow, rose heads can be very much higher.
Why you thnk only instant heating is usable for anything , I really don't know. Unless you want continuous showering at relatively low flow rates.

 

[jamsco]

8 lt/m? Thats not cool. A megaflow is definitely out the question with that and its not gonna provide you with a very good D/H/W supply through a combi either. Assuming your system is in good order have you looked at boosted mixer showers. Cover all the options before opening your wallet friend. Good luck.

 

[BigBurner]

Only instant hot water heating can cope with them

Shower towers with multiple heads aren't particularly high flow, rose heads can be very much higher.
Why you thnk only instant heating is usable for anything , I really don't know. Unless you want continuous showering at relatively low flow rates.

Some body jet showers use a lot of water. They are becoming very common. I noticed some developers are installing them in houses as they are a clear selling point. If you want to sell your house quicker and maybe get the asking price, fit one with a shower downlighters.

Only instant hot water can provide high flow rates for any length of time, that is why fast food outlets go for it.

If a body jet shower is 20 litres per hour, if the teenage girl is in the shower for 15 minutes (not a lot of time) that is 300 litres of hot water, then a lengthy reheat if the teenage boy wants to have a go too right after. Stored water can do it, but you will need 500 litres and that is one large and expensive unvented cylinder. Only instant on-demand DHW can provide high flow rates for lengthy periods. It is that simple. You should be capable of figuring that out and apply this rule when you are assessing new or updated systems.