What boiler for loft conversion

[Louis_sutton]

Hi all,
wondered if I could ask some advice as I'm uncertain about what my plumber is telling me. I am installing a loft conversion. I have a low flow rate (9.5l/min) and probably low pressure too. 3 bed semi, built in the fifties.

Conversion will include a shower room, separately I have a standard bathroom, plus downstairs wc. The two showers will occasionally be run together.

I currently have a vented system, so the cold water tank in the loft needs to be moved/removed. The plumber used by the conversion company keeps fixating on combi boilers and then telling me that I won't be able to run both showers. I've queried alternative options (pump on the mains, checking if increasing the supply pipe to the property will help, a storage combi, etc) but he doesn't comment. As far as I'm aware, I'm way too low on flow rate for an unvented cylinder. One option is to retain a coffin storage tank in the eaves storage I believe. Ideally I'd like to retain as much accessible storage as possible but, frankly, am just after a solution which works, and lets me dive in the shower even if one of my offspring is in the main bathroom.

I wondered if anyone would care to share some expertise? Confused by the fact that next door has one combi to run three bathrooms!

many thanks
louis

 

[Scott_D]

9.5lpm isn’t great and would be best to get this sorted first.
What is your incoming water supply?
Copper, plastic or lead? What condition is the stop tap?

 

[SimonG]

Electric shower in loft.

 

[Aire]

For your low pressure/flow system you definitely don't want a combi or an unvented. Your options are,

New mains, but you would need to speak to your local water authority to about what flow rates you could expect from doing so.

Keep the gravity supplies but use a booster pump. If you plan on using 2 showers at once you will need an absolute minimum of 50+ gallons of stored water though. And if your having a bathroom in the loft the pump will need to be negative, Your cylinder size will also need looking at as you can deplete the hot water very quickly if it's only a standard 900x450 cylinder.

You can also pump water either through a combi or an unvented cylinder. The cheapest option would be a large tank with a grundfos scala2, but a combi running 2 bathrooms with a good possibility of 2 showers at once might not be up to it, would need to be a big combi store but many will recommend an unvented over this.

You could also use an accumulator to either run an combi or an unvented. But as above a combi may not be the best option.

Personally it sounds like the plumber you have doesn't really have the knowledge to be undertaking the work you want, I'd look at replacing him as my first priority.

Your neighbours combi won't run 3 bathrooms, but it really depends on their usage as to whether it's actually an issue for them.

 

[Aire]

Electric shower in loft.

I wouldn't fit an electric shower to such poor supply. Someone opens the tap while your in the shower and your getting burnt or the showers switching off on overheat.

 

[Louis_sutton]

Thanks Scott - all questions I've asked the plumber actually, as I wasn't overly impressed that the visit to figure out a solution involved a quick look at both stop cocks. Pretty certain the pipe is copper (probably imperial from the little plumbing I've done around the place). Stop tap seems ok.

@Simon - thank you. I actually asked about that based on the fact that if he's suggesting running two combis, presumably I could run an electric shower (waiting on a response from that). I wasn't sure if low pressure prevents a combi and an electric running. Serves me right for living on a hill!

 

[Louis_sutton]

@Craig - thank you, that's really helpful. Starting to agree with your view that the plumber just isn't up to sorting a solution.

 

[Louis_sutton]

actually that's really very helpful Craig. Thinking a pump on the main with a combi and an electric might be a solution. But I shall bow to the experience of the plumber (once I have one who actually seems to know what they're doing...)

 

[SimonG]

Electric shower in loft is just the start. If there's two showers I like one to be electric. Nice back up.

Need to look at your dynamic and static pressures in conjunction with your flow rate.

Agree with Craig though, bin the current plumber.

 

[Aire]

actually that's really very helpful Craig. Thinking a pump on the main with a combi and an electric might be a solution. But I shall bow to the experience of the plumber (once I have one who actually seems to know what they're doing...)

Combi and electric would be a good choice, you can't just strap a pump to the mains though. There is the salamander home boost but that's restricted to 12ltm, and not really a solution to your problem. You can get tank pumped units for your mains but they aren't cheap that's why I recommended the tank in the loft and the scala 2 pump. I would first look at the option of a new mains though. Less future maintenance than pumped units.

 

[Louis_sutton]

ah gotcha. pump running from tank not mains. I'd started exploring mains pumps, mains pumps with tanks, etc etc. Thank you - would have been helpful if the plumber had sought a solution with us. Fair point on the mains - that feels like addressing the issue at source (no pun intended), so I shall see what the water company say re flow/pressure in the mains!

 

[ShaunCorbs]

Least you know where you stand if you get the figures from the water board

 

[Rob Foster]

aww. I have watched this one and..all my friends on UKPF have given their considered advice...mine is do not go there
in your position, we fixed one in Hightown ...Formby years ago..with a place with really
low water pressure and volume
some wally had put a combi in the roof space ...what a mistake
in a 5 bed big gaff.
Rob Foster aka centralheatking

 

[Louis_sutton]

Thanks for the help all - really useful to be able to have a proper conversation with the plumber!

 

[Rob Foster]

Thanks for the help all - really useful to be able to have a proper conversation with the plumber!

let us know what you do please
chking

 

[Louis_sutton]

Will do - it will be (in order), email to the water board to open discussions on what the main is like, discussion with/sacking of plumber, then move through (most likely) coffin tank plus pump, possibly with electric shower, and either retain the boiler or install a combi.

 

[Louis_sutton]

Affinity found 30l per minute and 4 bar pressure at the external stopcock. 9l/minute and 1.8 bar at the tap. New plumber incoming!

 

[Aire]

A new main will definitely give you an improvement then. Just be advised though that your current internal pipework may reduce those figures. 30ltm at the stop tap can reduce depending on how your house is piped. You want a 25mm alcathene main, 22mm stop tap or full bore lever valve, and if you can, replace your internal pipe work with 22mm main runs and branch off 15mm to each outlet.

 

[Louis_sutton]

well we started with a potential quick win and changed the internal stopcock. That's lifted flow rate to 16litres pm, and pressure is now at 3 bar standing, 2.5 working. so that's a nice improvement for a swift job. This plumber recommended keeping the boiler, and installing an unvented, seeing how we go and then adding pumps etc later on.

 

[Aire]

well we started with a potential quick win and changed the internal stopcock. That's lifted flow rate to 16litres pm, and pressure is now at 3 bar standing, 2.5 working. so that's a nice improvement for a swift job. This plumber recommended keeping the boiler, and installing an unvented, seeing how we go and then adding pumps etc later on.

16 litres a min is certainly an improvement and no doubt you have some restriction at the tap used for testing so your actual figure could differ slightly. Fitting an unvented and seeing how you go though isn't very inspiring from your plumber. He should know how it will work. You can test yourself. Open 2 outlets and see what your flow rate is at both. That will give you an idea of you can expect from a full mains system.

If your plumber is talking about fitting a pump later, does that mean a new mains feed is not an option you'll consider?

 

[Louis_sutton]

The plumber was mainly giving me options - there's a balance in how long we're going to stay in the property I think. If money (and disruption) was no object, then the mains pipe would be replaced. Really all I want is to know that if one of the offspring is taking a long shower, I can bop in and out for a fast shower and off to work. But a useful result for a very quick job.