Intergas xtreme 36 ok?

[bobbidill]

We're mid-renovation and now have to choose a boiler.
After searching and acquiring knowledge in forums, I was hoping you experts here might be good enough to share your advice too.
We have a 4 bedroom, 2 bathroom terraced house, which will be around 130sq. m with 66sq. m. - the entire ground floor and 1st floor bathroom - heated solely with underfloor heating via a 6 outlet manifold. There'll be 6 radiators in total.
We don't have enough space to put an unvented cylinder, which would have been my first choice and so we're left with a combi boiler.
I was thinking of going with the Intergas Xtreme 36, however many of our neighbours have much larger boilers, Vaillant EcoTech Plus 838 and so I'm now wondering whether this will be up to the task and wondered what the more considered views on this would be. Thanks.

 

[hard-work]

The Extreme I believe is just over 14 litre/min DHW. Your bathrooms? Do they have baths? Will you be using baths a lot rather than showers? Will two baths ever been filled at the same time (this is very rare)?

General points for main pressure systems:

• Fit a dedicated 22mm cold feed to the combi from the stopcock, irrespective of bore size of mains pipe. This assists in giving flow priority for the shower;
• Fit a full bore stopcock;
• Dedicated hot pipe to showers from combi/unvented cylinder;
• Fit combined isolators/flow regulators (using a cartridge for litre/min) on all H&C outlets - to balance the system;

You could use hot and cold manifolds with pipes to each outlet from each manifold. Then only 12mm pipe need be fitted to most outlets - 15mm for the showers. In softer water areas, even smaller bores. This gives quicker DHW delivery at the taps as the volume of cold water in dead-leg pipe is less.

Cylinders do take up lots of space, however look at using two combis, they could be on the same wall fitted high up, which takes up far less space (zero floor space). A 36kw & 24kw combi will be just below the limit of your gas meter - needs checking. Two 24kw Intergas Rapid combis are clearly below. One combi for upstairs CH and one for down so simple zoning. Always backup as if one boiler is down one is working. Also, split the bathrooms over the combis as well; one each. Simpler. You could join the DHW outlets using a couple of check valves for the DHW bath outlets only, then two 24kW combis will deliver about 20 litres/min to the bath filling up fast. I have done this (not in my place) working brilliantly. You may get a better deal buying two combis. You have two service costs of course, but could negotiate a better deal as two are on the same premises. But, an unvented cylinder needs an annual service as well, so evens out.

 

[Madrab]

Need more info

Heating requirements, what is the overall KW requirements for your UFH and radiators combined and has that been sized with suitable heat loss calculations?

Bathrooms how many showers - A combi, no matter what size, will struggle to adequately supply more than one mains fed shower at the same time. When any other HW outlet is used that would also reduce output to any other outlet/shower. Clever usage could be adopted by management of what's used and when, water saving devices etc but it's all down to what you want.

If hot water is a premium service to you, where you don't need to worry who's using hot water and it's all delivered at mains pressure/flow, then you really want to look at trying to wedge in a HW storage somewhere, if your supply can handle it with suitably sized distribution pipework. You'd be surprised where a professional could hide an unvented cylinder these days.

 

[hard-work]

A combi, no matter what size, will struggle to adequately supply more than one mains fed shower at the same time.

Just promoting unvented cylinders, which cannot be hidden, which suffer the same problems in water delivery as any mains pressure system such as a combi, is not too helpful. You need to get up to speed on combis, and multiple combis, and low litres/min Raindance aerated showers.

"Raindance EcoSmart overhead and hand showers consume only 9 litres of water per minute, while the Crometta 85 Green overhead and hand showers consume only 6 litres of water per minute."
​

https://www.hansgrohe.co.uk/bathroom/planning/technologies/ecosmart

 

[bobbidill]

The Extreme I believe is just over 14 litre/min DHW. Your bathrooms? Do they have baths? Will you be using baths a lot rather than showers? Will two baths ever been filled at the same time (this is very rare)?

General points for main pressure systems:

• Fit a dedicated 22mm cold feed to the combi from the stopcock, irrespective of bore size of mains pipe. This assists in giving flow priority for the shower;
• Fit a full bore stopcock;
• Dedicated hot pipe to showers from combi/unvented cylinder;
• Fit combined isolators/flow regulators (using a cartridge for litre/min) on all H&C outlets - to balance the system;

You could use hot and cold manifolds with pipes to each outlet from each manifold. Then only 12mm pipe need be fitted to most outlets - 15mm for the showers. In softer water areas, even smaller bores. This gives quicker DHW delivery at the taps as the volume of cold water in dead-leg pipe is less.

Cylinders do take up lots of space, however look at using two combis, they could be on the same wall fitted high up, which takes up far less space (zero floor space). A 36kw & 24kw combi will be just below the limit of your gas meter - needs checking. Two 24kw Intergas Rapid combis are clearly below. One combi for upstairs CH and one for down so simple zoning. Always backup as if one boiler is down one is working. Also, split the bathrooms over the combis as well; one each. Simpler. You could join the DHW outlets using a couple of check valves for the DHW bath outlets only, then two 24kW combis will deliver about 20 litres/min to the bath filling up fast. I have done this (not in my place) working brilliantly. You may get a better deal buying two combis. You have two service costs of course, but could negotiate a better deal as two are on the same premises. But, an unvented cylinder needs an annual service as well, so evens out.

Thanks Hard-Work. I've had to do a lot of reading around the points you raised! I've not been able to find anything which explains the mechanism by which fitting the combined isolators/flow regulators on all H&C outlets would help. How would this allow balancing the system please and why would this be necessary? As I'm very much learning as I go, I really appreciate those, such as yourself, with more experience providing your advice. If we can tolerate, waiting a wee while before the hot water arrives, is there any benefit to using manifolds? I hadn't even considered using 2 combi's so it's definitely in the mix now, particularly from a space viewpoint. Have you a rough idea what the cost implication of installing such a system would be versus a conventional one? Thanks.

 

[bobbidill]

Need more info

Heating requirements, what is the overall KW requirements for your UFH and radiators combined and has that been sized with suitable heat loss calculations?

Bathrooms how many showers - A combi, no matter what size, will struggle to adequately supply more than one mains fed shower at the same time. When any other HW outlet is used that would also reduce output to any other outlet/shower. Clever usage could be adopted by management of what's used and when, water saving devices etc but it's all down to what you want.

If hot water is a premium service to you, where you don't need to worry who's using hot water and it's all delivered at mains pressure/flow, then you really want to look at trying to wedge in a HW storage somewhere, if your supply can handle it with suitably sized distribution pipework. You'd be surprised where a professional could hide an unvented cylinder these days.

Thanks Madrab. Overall KW requirements for UFH and radiators are 5.07 + 4.12 respectively = 9.19 KW. Sized and calculated.
2 showers, unlikely both would be used at the same time, although it would be a nice option.
We just don't have room for an unvented cylinder.

 

[Madrab]

You need to get up to speed on combis, and multiple combis, and low litres/min Raindance aerated showers.

Been working with them all for years thanks. I very well versed with them all, have to be as I do advanced hot water design work for a lot of my customers. I do use combi's, water saving heads etc where cylinders weren't an option, mostly in flats though.

I can confidently state though that a well supplied, designed and maintained mains HW system will be very hard to beat by a combi or multiples of. All of these water saving showers, aereators and additions are all fine for water saving etc and if that's your bag then that's fine and they have their place especially the more south you go where water is more of a premium.
It just won't give you a skin tingling 3bar mixer shower @ 20+L/Min, which is exactly what a lot of people want. Hence my specific comment "If hot water is a premium service to you, where you don't need to worry who's using hot water and it's all delivered at mains pressure/flow" ... A combi or dual combi setup will still struggle to do that without being complicated and pricey.

If an unvented really cannot be catered for then of course alternatives always need to be considered,


..... 5 inline instantaneous electric hot water heaters for instance

 

[Dan Robinson]

.. 5 inline instantaneous electric hot water heaters for instance

In series or parallel?

 

[Madrab]

Sorry @bobbidill didn't mean to digress in your post.

Space heating isn't your concern as any 36kw combi will have plenty of headroom to supply all your heating. It's all down to hot water & how you want it delivered and how much you have to spend.

What can your incoming mains supply?

 

[Madrab]

In series or parallel?

Whatever take yer fancy ...

 

[bobbidill]

Sorry @bobbidill didn't mean to digress in your post.

Space heating isn't your concern as any 36kw combi will have plenty of headroom to supply all your heating. It's all down to hot water & how you want it delivered and how much you have to spend.

What can your incoming mains supply?

No problem Madrab! I have to be honest, I don't know what the incoming mains can supply. No problems with flow or pressure were mentioned when I asked about these though and we have a wide bore inlet pipe which I believe is 25mm.

 

[Madrab]

The cold mains dynamic pressure and flow information is critical to any well designed hot water system and no-one on an internet forum would be able to recommend anything suitable without it I'm afraid.

 

[bobbidill]

The cold mains dynamic pressure and flow information is critical to any well designed hot water system and no-one on an internet forum would be able to recommend anything suitable without it I'm afraid.

Thanks, understood. I’ll measure the flow and pressure today and post them. We only have 1 working water outlet though, so I’ll have to measure from this.

 

[Madrab]

Sorry to complicate things but you really need a dynamic reading ..... cold water running at one outlet while measuring at another. Can you tee off the single outlet you have just to create a temp 2nd outlet?

 

[hard-work]

Mains pressure systems (combi, thermal stores & unvented cylinders) have to be fitted properly, not having one 15mm cold mains pipe snaking around the house with the combi, or unvented cylinder, teed off it like it was just another sanitary appliance. Shower is king, all pressure and flow must be prioritized for the shower. Water takes the line of least resistance, make the shower hot and cold the least resistance in the system. It needs:

• Have its own 22mm cold feed from the stopcock to the combi even if the mains pipe is 15mm
• A full-bore stopcock
• Split the combi feed and cold outlets at the stopcock. Fit a tee for all cold outlets, except the shower. This can be 15mm in most cases.
• tee off the combi's cold feed, for the shower cold supply, just before the combi. Any flow pressure fluctuation around the combi will act of the hot and cold of the shower.
• have a dedicated hot pipe from the combi for only the shower.
• have the hot & cold outlets and taps on flow regulators (they are combined flow regulators and isolation valves) - you do not need firehose flow and pressure on bathroom basin taps, kitchen taps, toilet, dishwasher, etc.
• one flow regulator can do the dishwasher & washing machine which can get away with 6 litres per/min. In fact one regulator can do all the cold outlets, except the shower and bath, which should not be regulated.
• the shower hot and cold pipes should have no tees off these pipes. The shower hot & cold needs dedicated pipes.
• no flow regulators on the shower hot and cold.
• Use the equiv to Raindance shower heads, that consume less water.

Doing it this way it auto balances the hot & cold system to a large degree, the flow regulators on the the outlets fine tune the balancing, so no huge cold slugs while in the shower when the kitchen taps are turned on. This applies to all mains pressure systems.

Combined Flow regulator/isolator tap. A flow cartridge is inserted into the side - 6 litres/min, 2.5 litres, etc. A kitchen only needs 6 or 8 litres/min on hot and cold (I find it fine with 6), dishwasher/washing machine only 4 litres/min (a minute or so longer in the wash cycle is neither here or there), toilets can be 4 litres/min. 2.5 litres/min in a small downstairs toilet hand basin. Fit none on the showers.
Part number 17527 plus flow cartridges from 2.5 litres/min to 15.
https://www.bes.co.uk/flow-regulator-ball-valve-cp961-15mm-17527