Combi boiler and unvented water cylinder

[Mrslipmat]

Hi Guys

I,m looking for a bit of advice from the peeps in the know, hopefully the community will be able to point me in the right direction, I've tried searching but cant seem to find a conclusive answer to my question.

I moved into a small cottage in a rural part of Scotland August last year, the property is pretty much off grid so the heating and water are electric.

I,m looking at doing a long term change and in phases as finance allows, firstly I need to work with the hot water side of the system as the current tank fitted which is unvented uses two electric immersion heaters to provide the hot water, when the girlfriend visits with her youngest daughter, the daughter gets in the shower she seems to go through the 200l of water the tank provides which leaves everybody else waiting for water until the tank heats up again. We have one bathroom with, mixer shower, bath and one sink, the kitchen has one sink and we have a on suite with a sink and again mixer shower. Normally only one shower is used at any one time so demand is not a huge factor across all of the taps / showers

My first question is....

With us being off grid I,d like to fit a combi boiler running on LPG along with keeping the unvented tank with immersion heaters in for emergencies should we run out of gas, the current setup looks pretty standard and has the tank with mains water feed direct into it, this is then fed off to the various taps / showers in the cottage, Firstly, is it feasible to T off the cold water feed before the tank and pipe it into the combi boiler, then the DHW from the combi boiler is piped into the output side of the tank via a 3 way motorised diversion valve, the diversion valve is operated by the feed to the immersion heaters so when the heaters are on the DHW from the tank is usable, but when the immersion heaters are off the Combi boiler provides DHW on demand. Is this a feasible solution ?

Question 2, with the system being installed over time, the heating side of things will evolve as and when funds allow, in the meantime.... is it possible to pipe in the boiler too heating distribution manifolds which are blanked off, have a pressure bypass pipe installed and pressurise the system so there are no faults on the boiler, then keep the heating turned off until one or two radiators are fitted and expand the system from there, again is this a possible solution or even feasible.

I don't want to have to buy two different boilers as the system evolves and as such would greatly appreciate any advice good or bad along with suggestions.

Thanks in advance.

 

[picasso]

Just install a standard s plan with your combi boiler, you could use the outlet from the combi for a shower (never run out of hot water while there is enough gas )and let the system side heat the unvented cylinder to run all the other taps, the immersion heaters give back up if you run out of gas and you can install rads when the need arises.

 

[OwainDIYer]

Install the combi as S Plus plan treating the HW cylinder as a second heating zone (and fit a second timer)

However 200 litres should be ample for a bath let alone a shower so I suggest some parenting talk or fit a water restrictior to the shower outlet.

 

[Whitespirit66]

Yes, as above, flow restrictor is the answer. Friends had a similar problem with daughters, and fitted one. Don't think they really noticed, but the parents' gas bills soon reduced.

Fit one of these in between the end of shower hose and the male thread on shower unit.

http://www.sanliv.com/low-flow-restrictor-for-showerhead

 

[Mrslipmat]

Gents

Many thanks for your responses so far, the cylinder itself doesn't have a coil fitted so using the Combi to heat the water as well would be a no go unless the cylinder was replaced with one with a coil installed, that was the thought behind using the 3 way valve after the water outlet. I can specify a new cylinder if needed but just wondering what the overall benefits would be replacing it as apposed to keeping the origional and using the motorised valve.

Once again, thank you for your responses

 

[picasso]

I would replace the cylinder, you can get a 210 litre for under £400.

 

[Mrslipmat]

Hi Picasso

Thanks for your response

Am I right in thinking that if we change the cylinder to one with a coil fitted, a system boiler would be better suited to the application as apposed to a combi ? I know we would have a slight lag time wise in heat recovery for the tank but looking at some figures 30-35 minutes seems pretty good, far better than a immersion heater.

All in all there will be 11 radiators totaling +/- 44000 BTU so the boiler can be sized to suit whats required at the end goal. what we need to keep in mind is with the place being off grid and in the sticks so to speak Gas is at a premium so boiler size is key as we want to try aim for good efficiency.

The pipe work in the cottage is done in such a way that it would need replacing if I was to set it up so the Combi would run the showers while the taps / bath were done by the system side.

Regards

 

[muggles]

Ideally you should just have one or the other; either a combi or a hot water cylinder. Trying to split pipework so that a cylinder does part of the house and a combi does the rest is a pain. I'd be advising to ditch the cylinder entirely for now, fit a combi and see how you get on. If you're worried about a lack of hot water if the combi goes down, fit an electric shower

 

[shambolic]

Ideally you should just have one or the other; either a combi or a hot water cylinder. Trying to split pipework so that a cylinder does part of the house and a combi does the rest is a pain. I'd be advising to ditch the cylinder entirely for now, fit a combi and see how you get on. If you're worried about a lack of hot water if the combi goes down, fit an electric shower

Why is it a pain if he's doing it anyway?
I have 4 showers and 2 baths 5 WC/bathrooms in total.
My main ensuite shower runs off a 40kw combi as it has 20l/min shower head.
(Also another smaller shower in guest bedroom).
Rest of house comes off an unvented cylinder.
Works great.

 

[muggles]

I think he was intending to do it because he thought it was the only way round the present problem, which it isn't... I don't think your shiny new place could be described as a "small cottage", so the setup is bound to be different

 

[ScottishGasMan]

Personally I'd ditch the current cylinder, get a coiled unvented, and a system boiler, so you still have gas or electricity for water,

As far as plumbing in without rads your suggestion if fine, for combi or system boiler, how I've been doing my own place.

 

[Agile]

LPG is very expensive but probably comparable with electricity.

I have to say if I was there then I would be looking at a combination of solar panels and a heat pump to reduce energy costs.

But you don't say what you are doing there and if your income is low, medium or high!

There are so many different possibilities.

I would be reluctant to get rid of the cylinder. But a heating motor valve would not stand the pressure.

I would be inclined to fit a combi and use manual valves so the unvented is available as a backup if boiler or gas supply fails.

You don't say where you are but a combi takes a lot of gas and if in a very cold area that might give a problem with the gas supply if its very cold indeed.

An air to air heat pump is much more efficient that using direct electricity but the performance falls off when its freezing just when you want the most heating!

Tony

 

[Mrslipmat]

Gents

Thanks for your suggestions, just out of curiosity ScottishGasMan, what size system boiler did you go for ? from reading various threads some suggest its better to have as low KW rating as possible for efficiency ! bearing in mind we will only be using a 210 L storage cylinder and total btu's for rads will be 44000.

I appreciate all views for both systems and am weighing up all options, currently the only thing I,m trying not to change is the pipework to the current showers and taps, the original install was done 6-7 years ago and is piped in such a way that the feed from the hot water cylinder is 22mm, this is then T'd out with 15mm pipes to the various locations, almost in a branch configuration, the pipe work going into the on-suite is the end of the line on one side and reduced from 22mm to 15 mm which is split between the taps and shower mixer, current pipes run through stone walls that are about two feet thick and I suspect the last plumber went through several masonry bits as the stone is rock hard.

Once again

Many thanks

 

[Mrslipmat]

Hi Agile

I,m in a place called Reswallie just outside Forfar, the local council were not keen when I asked if it would be a problem to fit Solar, Costing is a concern at the moment as I work in the Oil and Gas industry and am not sure whats around the corner so to speak, trying to keep as much savings as possible until the upturn if it ever comes, however this could be a few years away.

The current system is regulated to 3.5 bar, I was just wondering if it was possible to automate the switch over process using readily available components which were easily replaceable off the shelf, however the immersion heater setup was for emergencies only if the gas ran out / or boiler failed. We do have wood burning stoves for heat as well so we wouldn't freeze per say and would still have hot water.

Again Gas usage is probably one of the main factors, I was thinking of having a bank of 4 X 47KG cylinders, access is an issue for oil and bulk gas.

Many thanks for your reply and valued input

Regards

 

[OwainDIYer]

On LPG I would not use a combi; it will fire up every time someone needs hot water. Also there is no backup. In a rural location having a cylinder of stored hot water, whether heated originally by gas or electricity, is useful when the gas or the electricity fails. For the same reason I would consider vented so that some stored hot water is available even with no incoming water pressure.

Also when calculating system requirements work only in kW; mixing kW and BTU makes things unnecessarily complicated.