advice please

[plumb_know]

Hi Everyone,

i am after your opinions/ views on what system would be best for a customer of mine, as i have asked several engineers and viewed different opinions on the web regarding required pressures/flow for combi boilers. this will be the first whole heating system installation i would of carried out as a business, so want to make sure i am advising the customer of right system to install.

customer has a bungalow 2 beds and 1 bathroom and conventional boiler with hot water cylinder in loft, but they are looking to do a loft conversion and extending ground floor changing it into 3 bed with 2 bathrooms and have expressed interest in combi boiler.

current Flow rate is 14 litre per min
standing pressure 2bar
working pressure 1bar

unable to see what material and size supply pipe is as boxed in behind tiles

i was planning to install a combi and have electric shower for one of the bathrooms, but have been given different advise regarding the performance these readings would give through the proposed set up.

so i would like to know what you more experienced guys would do in this situation, i have seen ideas of combi fed from breaker tank and salamander pump system for places where pressures has dropped so was thinking i could advise the customer of my concerns and if they still want to go ahead offer this as a possible solution if my fears are proven once its installed.

your wisdom will be much appreciated,

thanks

 

[Whyme]

Always good to have an electric shower especially as you have the option in case the boiler ever packs up. 10 kw if poss.

 

[AWheating]

your cold supply is suited to a med sized combi at most. What is the customers hot water demand? eg. number of people? hot water outlets? expected use?

the main issue will be that with the flow rate you have it will be shared across all the taps, both hot and cold. may not be a problem for an old couple, may be for a growing family.

what is the customers budget?

 

[plumb_know]

Thank you for the replies,

it's a couple in their 50's and the majority of the time it will be just the 2 of them but obviously second bathroom will be used when friends and family stay over. Regarding budget they have not given me a budget but obviously I would like to do it the right way as don't want it coming back to me 6months later and am prepared to lose the job if they are not prepared to do it the right way.

Is there a way for me to calculate what flow rate I would expect if both showers were used at the same time? And am I right in thinking that having electric shower will help improve the hot water demand slightly when used as it won't be passing through same small heat exchanger or will it make no difference as still mains draw off?

Appreciate the help guys

thanks

 

[cr0ft]

Hi OP, I think that with any sort of decent combi the limiting factor will be the 14L/m flow rate you've measured on the incoming mains. The electric shower will obviously heat it's own water but the combi boiler could most likely heat all 14L/m of that water satisfactorily anyway (check the MIs for the existing boiler).

14L/m isn't enough in my opinion. If a bath and shower are being run at the same time then either someone will be waiting ages for a bath or the shower pressure will drop right off. If this is an electric shower it will probably cut out if the pressure drops below it's minimum.

I would be costing up solution 1 (not upgrading the boiler) and solution 2 (unvented hot water cylinder and new water mains). You can actually use a combi boiler to heat a hot water cylinder so the boiler may not need replaced. In my opinion you definitely need some sort of stored water when you move up to two bathrooms/en-suites.

Give them the options in writing explaining the pros/cons and how it's likely to work. Get them to sign the one they want before you proceed.

 

[Ray Stafford]

In a borderline case like this, I would want to check that flow-rate again at different times of day.

You might find that 14 litres a minute turns into 9 litres a minute when the factory up the road turns their machines on, or some other peak demand factor occurs.

 

[plumb_know]

Thanks for the comments,

i have recorded the flow rate several times on different days and times of the day and it has been 14 litres on each visit

Keeping the old boiler is not really a option as very inefficient plus there will be no where to site existing gravity system when loft converted. I was looking at horizontal unvented cylinder behind a partition wall in eves but most manufactures recommend 20 litre per min and 1.5 working, and if I upgrade the mains there is no guarantee I will get that after is there?

Is feeding a combi via a breaker tank a option, would it work? As was hoping to email my concerns to customer and have this as a written solution to solving the problem if my fears are confirmed once it's installed. Then leave it upto customer to decide if they would still like a combi?

Or is there another solution I have not thought of bearing in mind the limiting space I have to work with.

Thanks for all the help people

 

[mountainman]

As already suggested, I would go for a combi say 28kw for everything other than an electric shower for the occasional use guest bathroom.

 

[cr0ft]

Thanks for the comments,

i have recorded the flow rate several times on different days and times of the day and it has been 14 litres on each visit

Keeping the old boiler is not really a option as very inefficient plus there will be no where to site existing gravity system when loft converted. I was looking at horizontal unvented cylinder behind a partition wall in eves but most manufactures recommend 20 litre per min and 1.5 working, and if I upgrade the mains there is no guarantee I will get that after is there?

Is feeding a combi via a breaker tank a option, would it work? As was hoping to email my concerns to customer and have this as a written solution to solving the problem if my fears are confirmed once it's installed. Then leave it upto customer to decide if they would still like a combi?

Or is there another solution I have not thought of bearing in mind the limiting space I have to work with.

Thanks for all the help people

Upgrading the mains will certainly improve the working pressure of the system. Going up one pipe size will improve this dramatically. It will certainly improve the flow rate too. If you have a 15mm copper mains upgrading it to 25mm MDPE will sort your working pressure and flow rate out.

 

[magicno1]

Forget the combi it will only come back and cause you grief!
find a home for a cylinder and use a universal/ negative head boost pump for your supplies.
considering how many houses are being crammed in now the mains will only get worse trust me.
we go storage every time now if we can and combis are really a last resort!
hth

 

[plumb_know]

Thanks croft and magic,

Ok I'm with you, as standing pressure is 2bar and working only 1 there must be resistance in pipe work due to under sizing on mains, by increasing mains size this should reduce resistance and reduce pressure difference between standing and working is this what your saying croft?

Also so magic you say feeding via booster pump, do you mean fitting this directly on mains? Or via a breaker tank like setup? As mains I could only pump 12 litres per min without water boards permission?

Thanks for all the help