Ahhh is there an M&E plumbing contractor in North East that can help me

[n141311]

would think if you wanted the re heat times as you stated with heating on the same time 100 kw is what you want, if your happy with a slightly longer re heat time (approx 20 mins more 80kw sounds about right)

rinnais are very good and can handle the load but its more cost (alot more) esp if you have already bought the cylinders but agree with his pressure/flow thoughts as hes on site

dont agree it will limit hot water temp, under sizing will only limit flow rate and esp if you havent got a secondary return it will add to the water draw off before it hot

you have two options (one you might not like)

one try and get as close as you can and re pipe in correct size (and hope its enough)

two re pipe the lot and either put the costs onto the inexperienced plumber for any damage to the walls / finish

best option is normally the worst sorry to say

sorry i couldn't be of more assistance

Hi Shaun,

Cylinders and boilers haven't been purchased yet.

What are the pros / cons of the Remmai solution vs unvented cylinders in your opinion? I'm concerned about the 3 things: instant hot water, delivered high pressure, in a cost efficient manner so I don't get killed by running costs

Appreciate your experience mate.

 

[ShaunCorbs]

Right ok (thought they had been )

Both if installed correctly will give instant hot water

Your water main governs both so no difference there

You need a high pressure water source either mains fed or tank and booster set (I would recommend the second if you have the space)

Usage should be about the same

One downside to the Rinnai's is more to go wrong than an unvented cylinder

Other than that there about the same

 

[n141311]

Right ok (thought they had been )

Both if installed correctly will give instant hot water

Your water main governs both so no difference there

You need a high pressure water source either mains fed or tank and booster set (I would recommend the second if you have the space)

Usage should be about the same

One downside to the Rinnai's is more to go wrong than an unvented cylinder

Other than that there about the same

Gotcha. Ok so my thinking is if I have a breakdown, I really don't want to stuck trying to find a plumber that can sort it. appreciate your other points - didn't realise it was virtually identical in all other aspects.

Got another thought: if we upgrade where we can & pray...there is still the rest of the house yet to be piped up. If we do that properly, will those other rooms at least get high pressure water without any issues? Or are we now f* through the whole house because part of the piping is in wrong size?

 

[ShaunCorbs]

The only part that will be effected is the bits he's done / you can't get at

If the other parts / the rest is done right / to what somone works out they should be fine

(Hope that makes sense)

 

[n141311]

The only part that will be effected is the bits he's done / you can't get at

If the other parts / the rest is done right / to what somone works out they should be fine

(Hope that makes sense)

Thanks mate. That message made my night. Have been crapping myself thinking the whole house might be compromised. Thankfully the guy only did 4 rooms.

 

[ShaunCorbs]

We're all here if you have any other questions / want to pass somthing by us

 

[n141311]

Hi all

Hi mate
Sorry I didn't ring you back. I didn't save your number, so could you ring again?.
Pm sent too.

Hi mate, no worries - I replied to your PM? Did you get it? Can you also let me know the following (forgive me for asking but I've been burned by one plumber so figure I should ask Qs up front):

- what's your trading name
- are you gas safe registered for unvented system installs (I think this part F cert or something)
- do you have a commercial ticket / able to install boilers at 65kw - 100kw (I don't want to go anywhere near 100kw due to monthly heating bills)
- are you insured for your work
- are you VAT registered (impacts whether I get hit with an extra 20%. ouch)

Feel free to PM me on the above and let me know if you got my mobile number from the message I sent you. I'll text you if not.

 

[n141311]

Hi all,

So did some additional thinking based on messages from yesterday. Wanted to share and get thoughts based on people's input so far.

- Achieving that 25 litre per minute reheat capacity on two cylinders (12.5 litre per min * 2 cylinder) will require an upgrade of boiler from current proposed 50kw to 100kw
- But this would effectively double my monthly gas heating bill assuming I'm using boiler for same amount of time but its consuming 100kwh instead of 50kwh :O

Therefore, I did some thinking around how to lower flow rate demand through the pipes and from cylinders:

MID CASE DEMAND (MOST REALISTIC)

• 7 bathrooms (not 8) to be used during peak times for av. 10mins
• each shower will have flow rate of 9.5 litres per min instead of 11.5
• Litres per min used: 66.5 (9.5 x 7 showers) (total demand over 10mins = 665 litres)
• At 600 litres cylinder capacity, house will run out of hot water in 9 minutes
• However if boiler is able to re-heat two cylinders at 12.5 litres a minute (6.25 l x 2 cylinders), in that 9mins, an additional 113 litres of hot water would be available due to reheat capacity (9 mins * 12.5 litres per min reheat)
• This gives a total capacity of 713 litres of hot water (600 litre core capacity + 113 litres reheated over 9mins)
• NOTE 1: the 600 litres in 9 minutes indicates a flow rate of 66.5 litres per minute from the cylinder - Would this also require installation of a pump to support that kind of flow rate out?
• NOTE 2: At 66.5 litres per minute from cylinder + 12.5 litres per minute recharge capacity = 79 litres per minute flowing through the pipework
• NOTE 3: The above takes no account of radiators, toilets being flushed or sink basins being used. Should I factor more for this?
• NOTE 4: Assumes the 8th bedroom which is a staff room will not use the shower during peak periods

I'm taking a guess here but based on lower re-heat capacity of 12.5 litres per minute (6.25 litres per min x 2 cylinders) - what boiler size would I need? Could I get away with 65kw?

RUNNING COSTS

• KwH boiler: 65
• Hrs used per day in winter: 6hrs
• Total KwH per day: 390 (65 x 6 hrs)
• Total KwH per month: 11,830
• GBP per KwH: 0.06
• GBP gas bill per month: 710

• Winter demand assumption is that heating will run for 3hrs in the morning and 3hrs in the evening. Is this realistic based on modern u-value homes?
• Finally, not sure if all of the above is based on faulty logic because of the way the unvented cylinders would work, ie. boiler usage will actually be a lot less than 6hrs as cylinders will keep water hot minimising need for boiler to be hammered during heating periods? Let me know your thoughts.

Thanks to everyone who has helped out on this thread so far. I can't explain how much it has helped me get through this nightmare. I'm posting updates so a) others can learn and hopefully benefit from it b) to see this thing through to the end with hopefully a happy ending

 

[n141311]

I think you should seek advice from a company, or consultant, who does a lot of this type of work. It definitely looks 'commercial' not 'domestic' to me and needs to be 'designed' not lashed up using rules of thumb.

The assumptions you put in about what performance is needed at periods of maximum demand are going to make a big difference to the cost and performance of the system. E.g. where did you get the '20 mins' average figure from? The average (domestic) shower apparently lasts 8 minutes:

People's showering habits revealed in survey - BBC News

and that average includes teenagers!

I imagine that, if one knows where to look, there are data available for shower usage patterns in hotels.

Hi @Chuck - forgot to stay thanks. You're spot on with that point about ave shower times. I ended up revising down from the crazy 20mins (based on how long my wife takes!) to a more realistic average of 10mins

 

[Chuck]

Hi @Chuck - forgot to stay thanks. You're spot on with that point about ave shower times. I ended up revising down from the crazy 20mins (based on how long my wife takes!) to a more realistic average of 10mins

You're welcome.

I've only skim-read the rest of the thread as you seem to on the right track and it's looking like site-specific details. I will point out one incorrect assumption you seem to be making in your revised estimates, which is that a 100kW boiler will cost twice as much to run as a 50kW one. This is not going to be the case because if you want to heat a certain number of litres of water, e.g. 8 showers worth, the gas required will be the same in each case. The 100kW boiler will just be able to deliver it in half the time.