Whole House Plumbing advice / help desperately needed !!

[fr33z1ng]

Hi all hope you can help me with my dilemma.

Scenario : 1950s built detached house in London
Approx 150 sqm Ground / 140 sqm 1st Floor / 100 sqm 2nd Floor
Double Glazing Argon Filled Low E Stuff
Pitched Roof with 100mm Celotex
Walls Cavity with insulation
6 Bedroom
5 Bathroom (3 Shower / 2 Baths)
10 Radiators ( 7 on 1st Floor / 3 on 2nd floor)
5 Towel Rails (Water Heated)
Shared Occupancy (7 Adults / 4 Children)

Typical Evening Usage : 8 Showers + 1 Bath to be taken approx 10 min each over a period of 4 hours - possibility of Bath run at same time as 2 other Showers.
Typical Morning Usage : Washing up / Washbasins / 2 Showers one after the other over a period of 2 hours.

Underfloor Heating on Ground Floor (approx 700m pipe) - covered in tile over 100m2 and 18mm wood over 40m2.

I have had 3 plumbers come in to design system..hence dilemma

Plumber 1 : 2xBoilers Keston 28 Qudos + 1x400l Unvented Tank
Plumber 2 : 1xBoiler Valliant 837 + 1x500l Unvented Tank
Plumber 3 : 1xBoiler Veissemann 200W 35Kw + 2x200l Unvented Tanks

Which of these will provide me with the most efficient system and enough water for my purpose - I also have 700m of underfloor heating to consider.

Underfloorheating only requires water @ 30 deg is there a boiler which can have such an output for 1 zone and 80 deg for another ( water tanks + radiators + towel rails ) ? Or is this not the right way to go about things - I want max condensing for efficiency ?

Is one 35kw boiler better than 2x18Kw ones? I was thinking perhaps run 1 tank and underfloor heating off one and another tank and rest of heating /rails of the other ? System would be a s-plus plan ? 4 zone Hortsmann programmer ? would it be wise to run the tanks in parallel or split 1 tank for kitchen + 2 bathrooms and the other for the remainder 3 ? How about in parallel and manually switching one off in summer when demand is not that high ?

Apologies in advance for the lengthy note but wanted to provide as much info so I could get some realistic feedback.

 

[tamz]

Ask 10 plumbers and you will get 10 different answers.
Personally i think plumber 1 has the best idea but i don't like Kestons (i used to mainly for the flueing, but they became a source of trouble and have a bad rep and may have improved).
A 400 litre cylinder should provide all the water you need but you should restrict the flow through the showers.
The underfloor heating water is supplied through a blending valve which can be set to whatever you require regardless of the flow temp. Get the underfloor designed for you. Manu's do it for free.
In this situation 2 boilers cascaded would be a better idea than 1.
It is too late to think about this much so these are just quick answers.

 

[fr33z1ng]

Thanks for the reply !

Can you explain some more about what 'cascading' is in terms of boilers ?

Also, if I went for a 2 boiler setup any suggestion on power output ? will 2 x 24kw do ?

Any mkaes to avoid i.e. keston as you have mentioned.

Any particlularly reliable boilers ? what about Worcester Bosch or Veissmen ?

 

[BARTMAN69]

Go for Worcester bosch,using accredited installer to give you 5 year warranty,supply heating thru low loss header, made by VA heating,(look on internet for site)HW water depends on occupency and the structure of the building to take weight.Dont over size boilers.dont use Keston unless flueing option is restricted.and it goes on.

 

[Centralheatking]

I think it would be a good idea to present this to Vaillant/WorcsB/1 other technical sales dept and get them to specify - then find an installer. This is a big building and your wants are specific so it makes sense to get the manufacturers to do a bit for free.

I also have my ideas which could futher confuse things.

Whats your budget ? this is not a cheap system

centralheatking

 

[doitmyself]

Scenario : 1950s built detached house in London
Approx 150 sqm Ground / 140 sqm 1st Floor / 100 sqm 2nd Floor
Double Glazing Argon Filled Low E Stuff
Pitched Roof with 100mm Celotex
Walls Cavity with insulation

Have you done a heat loss calculation?

If not use Boiler Size Calculator. You will then have a good idea what size boiler you need just for heating.

As for hot water, it does not matter what size HW cylinder you have if the incoming mains is not able to deliver the required flow and pressure. So if you have two showers and a bath running at the same time there could be a requirement for 30 to 45 litres per minute.

You can check the flow rate at the kitchen sink cold tap using a marked bucket and a watch. If you have a garden tap straight off the mains, do the test with the garden tap closed and then with it open. The rate with the garden tap open is the important one, but the lower the difference the better. Don't forget that everything will be fed from the incoming mains - showers, baths, toilets, washing machines etc.

 

[doitmyself]

Have you done a heat loss calculation?

If not use Boiler Size Calculator. You will then have a good idea what size boiler you need just for heating.

Just done a quick calc using the above link

Assuming three rectangular floors each 15m x 10m, I got a result of approx 23kW. So how does one installer come up with a 35kW boilers?? The other two aren't far off the mark, but feeding a HW cylinder from a combi boiler is unusual.

 

[fr33z1ng]

I tried on some boiler sizing websites and I too got around 22kw.

But surely this is heating only ( I have been quoted 12kw as required for the underfloor heating by a supplier).

Would the 12 Kw left over from a 24kw boiler be enough for the rest 1st and 2nd floors ?

I see that 2kw is added for heating water - this sounds far too less ? and surely would mean recovery times of hours instead of minutes - I am out of my depth here so pls humour me if this is not the right thought process !

Heatrae Sadia I spoke to yesterday and they said their tanks have quick recovery as long as the boiler is powerful enough - enough means what in laymans terms ?

This still leaves me with not fully knowing if for example a Worcestor 30CDI for is going to be able to handle all the requirements ? e.g. water / heating / underfloor - all calling for heat at the same time e.g. cold mornings through winter months.

 

[fr33z1ng]

Just realised typo in first post - Valliant 837 should have been Vaillant ecoTEC Plus 637HE


was 2 in the morning !

 

[fr33z1ng]

Central Heatking asked about budget set aside - approx £15k including the underfloor heating

 

[ecowarm]

Viessmann can do the lot from one boiler 200-w and a correctly sized vitocell cylinder, different temps to different zones ie underfloor and rads. also weather compensated.

35kw way over sized i'd be looking low 20kw + Hot water demand

give Viessmann a call and see if the will recommend a installer in your area

Eco

 

[stevetheplumber]

the advatage of two boilers is your never without at least some heating and hot water and generally speaking they dont work out much more exspensive even the best boilers breakdown and usually just when you need it most

 

[fr33z1ng]

Thanks for all the replies and information so far - you guys are really helpful

I will speak with Veissmen tomorrow and find out what their thoughts are.

Just out of curiosity - 3 zones all want water at different temps albeit at the same time.

How would a boiler handle that ?

I understand system boilers have flow/return for 2 circuits i. DHW and CH so in theory one could set the DHW to 70 deg and CH to 65 ? but what about the underfloor heating - if this is tee'd off the heating circuit with a zone valve - boiler will still send down water at 65 deg only to be dropped down to 30 deg by thermo valve in underfloor heating manifold for its usage. This would be inefficient as return to boiler is no where near the 54 deg mark which is ideal for condensing ? and also boiler unnecessarily running at higher temp than what is actually needed ( if only underfloor heating was calling ).

Does this mean that in order for the boiler to work effciently and in condensing mode - CHW and Underfloor heating should be on both together or CH only and not under floor heating on its own - what impact does the much cooler circuit from the underfloor heating have when combined to the return from the CH circuit - would this not also bring down the temperature from the desired mid 50' degC ? e.g mixing hot (55deg) with cooler water (27deg) ? and again not encouraging boiler to condense ?

I am just trying to get my head around this so pls be patient with my questions ..

 

[ecowarm]

the Viessmann 200 can do different zones and temps at the same time

you can run the underfloor direct from the boiler with no mixing valve. if you use their unvented cylinder it does not need a seperate 2 port valve, the boiler controls the hot water temp.

 

[tamz]

A Viessman or no other boiler can supply water at different temperatures for different circuits at the same time. What it does is an inbuilt divertor valveis fitted and some smart electronics ramp up the power when the valve opens. That puts the full output to the water when required then cuts back to the other circuit when satisfied.
A 4-500litre cylinder will have a coil rated at around 30kw. To give recovery rates that are anywhere near what a manufacturer quotes the full boiler output has to go through the coil ie divertor valve and the flow temperature would have to be around 75° to achieve this.
2 boilers might be better than one for reasons among others previously stated by steve.

Speak to the manu's and see what they recommend rather than us lot throwing different things in the mix. They will design and recommend the best system for you. As i said 10 guys will give 10 different answers.
Viessmann are good boilers btw.