Electric combi boiler for underfloor heating and rads - off the grid

[serfer]

Hi all,

I'm new here and trying to get my head around the selection of boilers as none of them seem to have very detailed spec sheets. My property is off the mains gas grid, with no space for LPG or oil tanks. I can't afford biomass or air source pumps which leaves me with an electric boiler.

I would like the boiler to run the underfloor system, radiators and domestic hot water for a 3 bed, 2 bath home.
I would like it to be a combi boiler.

Anyone got any ideas of a good model?

Thanks!

 

[lame plumber]

move house it will cost you the earth to run or find room for an oil tank, they can be buried!

 

[serfer]

I have no space even to bury the tank.

Moving house use isnt really a helpful idea! I am looking for advice and assistance. I know electric combi may not be the cheapest option in terms of per unit of fuel, and I dont want to discuss running costs, refuelling, installation or servicing costs.

I am just wondering what electric combi boiler would be suited for ufh and rads and domestic hot water.

thx all

 

[SimonG]

You dont want a combi. You want an unvented direct cylinder heating up on cheap rate. Thats if you have the water pressure and flow. Then you need an amptec for your underfloor and an amptec for your rads. Then big pockets to pay the leccy bill.

 

[serfer]

No. Cheap rate isnt an option for me as I have huge amounts of electric running during the day / when the rate would be much higher than usual.

I save hundreds on installation and maintenance and I have very little space so combi electric is the way to go. This much i know and i dont need to hear alternatives thx v much for the input, but i really just would like thoughts on good electric combi boilers for rads, ufh and domestic hot water!

 

[SimonG]

Electric combi is not thecway to go, it wont do what you are after. Simple as, but what do we know, eh! Good luck.

 

[lame plumber]

customer always knows best................................

 

[Masood]

Simon is right, serfer. Electric combi will not give you anything like the flow rate of a gas boiler. To heat UFH and rads a smallish Amptec will do the trick. Direct unvented for hot water. It's irrelevant that you use loads of electricity during the day - the cheap rate you use during the night will still save you some money. If you're really not concerned about saving money then just run the immersions 24/7.

 

[gasmanrob]

Look at the electric heating company based in Scotland I've fitted a few of their units and they seem to be ok that said they have only ever been fitted in flats and one guy moved out 8 months later due to running costs.

To to get the heat load you need your going to need a 3 phase supply to run an average house electrics day to day plus allowance for maximum load in winter.

Personally for what your asking/adamant on doing I'd get 2/3 heatrae sadia inline boilers (tall slim pass through type) in tandem linked with an unvented hot water cylinder fed via a heavy duty water softener.

Id is also get solar panels on the roof. I know you've stated that the cost of renewables is out of your range, but you can get them free you won't earn a penny out of them like the people who own them but youll
be making a start on reducing an astronomical running cost.

And nod although you say there is no room for the alternatives, there is always a way always. How can you live of the beaten track cut off from mains gas and not have space? Equally if you are off mains gas I can't imagine you will have an overly adequate electrical supply

 

[chris watkins]

I save hundreds on installation and maintenance and I have very little space so combi electric is the way to go.
This much i know and i dont need to hear alternatives thx v much for the input, but i really just would like thoughts on good electric combi boilers for rads, ufh and domestic hot water!

If this much you know why are you bothering to ask on here?
The bit you clearly don't know is the basic laws of science & the limitation of the domestic house electrical supply.

We wouldn't even be recommend that you install a gas fired combi to supply the hot water to your two bathroom house at around 30kW it would provide a very poor hot water flow & not be able to provide the heating at the same time.
Lets just say you went with an electric version.
30kW = 30,000watts / 230Volts = 130 Amps, have you checked the size of your cut out fuse on the incoming electric supply to your house, if not go take a look.

 

[Nostrum]

Hang on. What have you got that's currently running the underfloor etc?

 

[Nostrum]

Are you a landlord?

 

[serfer]

Thanks everyone for the information! Its really helpful to get pro input. I own a little cottage, for me and family to live in, with no land, out in the country off the grid. There has never been a heating system in place - just a few old wood burners.

I have been been investigating heat source and distribution since November and have resigned myself to having no option other than electric. Or 47kg bottled calor gas. I really don't have much room downstairs (trying to start running a business from home that needs equipment and loads of storage) and the loft is 350yrs old and cant take the weight of a tank up there.

Re the electrics - I have just had the PME update for my earth and I'm running 60amps until my metre gets updated when I could go to 100A. The electric hardware, cabling, sockets and all will be done entirely from new next month.

I imagine the 75sqm ufh will be running a lot. 6 Upstairs rads used sparingly if at all. Really dreading the thought of high running costs. Why is combi no good? Is it because it would always be running?

 

[Gray0689]

It would work out cheaper to run cylinder gas than electric

 

[serfer]

In dorset the electric is 10p per unit. Cylinder gas is around 14.5p...

 

[Rickster123]

I'm lost. If you already have all the answers what was the question?

 

[serfer]

Electric is my only option but... I'm wondering why combi would be very expensive to run when compared to another electric system...

 

[chris watkins]

Why is combi no good? Is it because it would always be running?

Because it take large amounts of energy to heat water instantaneously (4.186J/degC/Litre).

That 30kW gas fired combi I was talking about will deliver something like 12Litres a minute @ a 35deg C rise in Temp just enough to supply one tap properly. If we took all of your current electrical supply & used it all to heat hot water it would be equivalent to a 13.8kW combi (60Amp x 230V=13,800w).
Get the idea ?
Ever used an electric shower ? they are limited to around 10.5Kw for a reason & you don't get a good shower out of them in the winter do you.

 

[serfer]

Heating water instantly?
I was hoping to find a combi with an internal store of 50-150 litres that is kept ticking over at a good temperature...

 

[lame plumber]

Heating water instantly?
I was hoping to find a combi with an internal store of 50-150 litres that is kept ticking over at a good temperature...

you dont seem to be listening to anyones advice at present!!

 

[serfer]

I'm listening but i get confusing information. I am told that a communism expensive because it needs to heat water instantaneously, but then i am also told that combi boilers have a store and just need to trickle heat in to keep the store nice and hot... The advice is also conflicting about what type and number of boilers i may need too. So while I am listening, when a question mark appears based on that advice, I will follow it up as best i can. I hope rather than personal remarks we can focus
more on answering the questions raised.

 

[Dotty]

Not seen any conflicting advice on this thread, you've been told countless times what you want cannot be done and why.

Have you ever heard of confirmation bias?

 

[SimonG]

I hadnt heard it as confirmation bias before, I normally hear it as 'wont be told'.

 

[lame plumber]

dont you mean, thats not the answer I want, so go away

 

[chris watkins]

We do our best, free of charge to help people, there is no confusion its the laws of science as I have already stated & tried to explain.

Its not our fault you can't take what you are being told onboard & don't know what a combination boiler is.
Sorry me old fruit but I am out of here!!! :waving:

 

[serfer]

I'm just confused as there are different models mentioned above, one mentions a a smallish amptec would suffice, another mentions having 2 inline, one serving each distribution method. Another mentions not even a powerful gas combi would cope. So its a bit confusing!

 

[Masood]

Heating water instantly?
I was hoping to find a combi with an internal store of 50-150 litres that is kept ticking over at a good temperature...

Guess what you've just described? Yep, you got it - a cylinder!

 

[serfer]

If a combi has an internal store - then why would i go for a cylinder? Or rather, if I want a cylinder, then why is the combi a bad idea? I was lead to believe by a plumber not on this forum that a combi would have a store... So i dont know what to make of it all!

 

[Deleted member 64964]

Guess what you've just described? Yep, you got it - a cylinder!

No its a electric combi boiler with thermal store and an immersion to heat it, its completely different to a cylinder. This think you can get in different sizes and is cylindrical in shape. :blush5:

 

[serfer]

thanks Therm! can you sense my confusion? Masood tells me I'm talking about a cylinder. you like his comment, then you say i'm talking about something completely different.

I'm going to look into the cylinder option, unvented direct, as suggested above, but then chris' comment worries me! Chris seems to be saying that i don't have the electricity supply to deal with an electric boiler of any type?

:disappointed:

 

[SimonG]

The irony of it.

 

[Deleted member 64964]

thanks Therm! can you sense my confusion? Masood tells me I'm talking about a cylinder. you like his comment, then you say i'm talking about something completely different.

I'm going to look into the cylinder option, unvented direct, as suggested above, but then chris' comment worries me! Chris seems to be saying that i don't have the electricity supply to deal with an electric boiler of any type?

:disappointed:

Direct unvented cylinder is your best option. Don't worry about any other posts about hot water. That's your best option without doubt.

It's the most cost effective way and once it's hot it's just a matter of a tickle ro get back to temperature.

 

[chris watkins]

Direct unvented cylinder is your best option. Don't worry about any other posts about hot water. That's your best option without doubt.

It's the most cost effective way and once it's hot it's just a matter of a tickle ro get back to temperature.

I know, I know, I said I was out of here but just a word of warning serfer what you have been told a number of times is correct storing hot water in a cylinder is the way to go cos you can use the energy over a longer period & so it doesn't have to be so powerful, most immersions are 3kW you just have to have em switched on for a good fuse hours.

You started by saying you are on a tight budget but you must understand that the installation of an un-vented cylinder (well any actually) is subject to the Building Regulations AD Part G & as such it is both illegal & dangerous to try to install one yourself "YOU HAVE BEEN WARNED"

Get a plumber in who has their ticket & can self cert the install, they can advice you of the best options & limitations.

Bye CW

 

[cr0ft]

If a combi has an internal store - then why would i go for a cylinder? Or rather, if I want a cylinder, then why is the combi a bad idea? I was lead to believe by a plumber not on this forum that a combi would have a store... So i dont know what to make of it all!

I will try my best to explain. As far as electricity goes you have 2 options available to you. Use cheap off-peak electricity to heat your house (last time I checked this was available for as little as 6p/KWh compared to around 15p/KWh for peak rate electricity). There are even Economy 10 tariffs now available that give you 3 off peaks in the afternoon. Use this electricity to power immersion heaters during this time to heat the largest hot water cylinder you can fit in your property. The energy in this is then stored and used when required to run normal central heating, underfloor heating (plumbed not electric) and heat hot water on demand. These modern cylinders are very heat efficient and will retain nearly all of their energy over a 24 hour period.

As you've mentioned already, cylinder installs are more expensive so you would save money initially by not purchasing a cylinder. This saving will be eaten away in no time at all by paying 15p/KWh vs 6p to heat all your hot water and run your central heating. I can't really make this any clearer so I hope it makes sense!! Effectively your cylinder is like a giant energy battery that stores up off-peak energy and uses it in the peak times.

This is the only cheap way to run an all electric house. If you size the cylinder correctly it will be cheaper than any other fuel type except mains gas. If the cylinder is too small you end up using peak rate electricity and the system costs a fortune to run.

My experience in this? We fit these systems fairly regularly and so I know they work and how cheap they can be to run.

At present a 60A incoming supply to your house isn't sufficient to run one of these systems though (they nearly all draw 52A, running 4 immersion heaters at once usually) which doesn't leave enough left to boil a kettle. Ask your supplier to upgrade you to a 100A supply. This is often free if you can demonstrate why you need it.

 

[village idiot]

Phone up any of the major underfloor heating company manufacturers (Uponor, WarmUp, etc) and provide them with your scenario. They are better able to assist you. Good luck

 

[serfer]

Thanks croft! Really useful and very much appreciate your time and patience!
I was lead to believe that economy 7 or 10 would increase my peak rate by quite a lot. So instead of 10p per unit 24/7. I pay 6p for 10hrs and 15p for 14 hrs. My business will be using quite a lot of electric to power the equipment so i wasn't sure about going economy 7 or 10...

 

[serfer]

also, one more question: why direct cylinder? If i am getting a boiler, wouldn't an indirect be an good option?

 

[SimonG]

Have you ever heard of the horse, the water trough and the two bricks?

 

[serfer]

Not yet, no!

 

[Chalked]

Not yet, no!

dont mean to be blunt but! For example.
Why would you use a 3kw boiler to heat a cylinder with pumps etc. that you can heat with a 3 kw immersion heater?

the op needs to realise that electricity is 100% efficient, but costs 3 times per kw than natural gas.

 

[serfer]

Aha. Gotchya! So boiler is eg 9 or 12kw. And immersion in a direct cylinder is 3kw. I see i see . Thx chalky and all

 

[serfer]

so.. is an immersion heater the same thing as a direct cylinder? last question i promise. probably.

 

[Gray0689]

The direct cylinder is heated by immersions
Indirect by a boiler or the like

 

[cr0ft]

also, one more question: why direct cylinder? If i am getting a boiler, wouldn't an indirect be an good option?

No need to get a boiler. You only need a boiler if you are going to be on mains gas. Off-peak electricity is cheaper than all the other fuel types. You just need the cylinder to be sized correctly so it holds enough hot water (i.e. stored energy) to satisfy your hot water/heating demands in the peak rate times. The cylinders in question work in reverse to normal cylinders. The immersion heaters heat the water in the cylinder. The heating circuit water passes through a heat exchanger in the cylinder and takes energy from the cylinder water itself. Make sense?

You can run underfloor heating off these no problem in fact a UFH system works better on these than a normal radiator setup due to the lower temperatures UFH runs at.

Take a look at this system - this would be perfect for you: -

THERMAflow

Make sure you get someone who knows what they are doing to size and install it for you or it will be the most expensive system to run you could imagine.

 

[cr0ft]

dont mean to be blunt but! For example.
Why would you use a 3kw boiler to heat a cylinder with pumps etc. that you can heat with a 3 kw immersion heater?

the op needs to realise that electricity is 100% efficient, but costs 3 times per kw than natural gas.

Off peak electricity is much closer than that to the cost of natural gas though. If he doesn't have access to natural gas in the street an off-peak electric system is cheaper to run than LPG or oil.

 

[serfer]

Thanks for the info croft... The thermaflow link is selling me electric combi boilers... Which was my first plan. But the consensus seemed to be to avoid the electric combi due to run it costs.

What at does anyone else think? Is a direct unvented cylinder enough to run 6 rads, 75sqm ufh and dhw? Would a boiler be needed too? Would 9 or 12kw be best... Loads of fun this plumbing malarky! A fair bit to get me head around and thx again for helping

 

[chris watkins]

Can you have yourself taken off of a thread ???????? this is starting to do my brain in.

serfer please for the sake of god get a local guy to come in explain the options & give you a quote, you are getting yourself all tied in knots & it is certainly not fun, in fact I am starting to think this is a windup.

You keep using the term "combi" a combi to us is a boiler (gas or oil fired) that heats water instantaneously you turn on a tap and we have done that one haven't we??

What croft has suggested is an electrically heated thermal store, the heat is stored in the primary water & can be used to provide heating for the house &/or domestic hot water (taps) via a plate heat exchanger.

An un-vented hot water cylinder can not be used to provide heating for your house only hot water from your taps.

You are right about the cost of peek rate electric when on an Economy 7 tariff it tends to be higher than if you were just on a standard rate but we can't help you with that can we ?? You need to look at you day time usage & get some quotes.

One thing you have found out is just how much "FUN" it is living & working in a small old property in deepest darkest Devon & if you think you are poor now wait to those bills start to roll in.
There was a good reason why they stuck to logs burners !!!!
Now for the very last time bye.

 

[serfer]

electric combi boilers are common place - they appear all over the internet, and in Croft's link.. it clearly mentions 'electric combi' on the first page...

these electric combis (their word NOT mine) have an internal store of 150 litres or so. so to me it seems like they call it an electric combi, and you guys call it an electrically heated thermal store and thats fine by me, just want to use the right terms to make sure i'm on the same page as you all.

so i want an electrically heated thermal store AND a plate heat exchanger? never heard of a plate heat exchanger, is that a seperate bit of kit, or does it come inside the thermal store?

 

[Gray0689]

Get a plumber in to talk to you direct on the job and explain as you are not either listening or grasping the concept

Get an electric boiler to do the heating side
And a direct cylinder to do domestic water

 

[serfer]

Thx Gray. I bet this must be painful for everyone and its great this community exists to help folks like me. Electric boiler and direct unvented cylinder. Yes. Got that agree! Sounds great. I understand.

But chris and croft have mentioned a thermal store.

A) you don't agree with their advice
b) a thermal store is another way of describing either a boiler or cylinder...

Theres so many terms its confusing. I dont know if everyone is using different words to talk about the same things or if you actually have fundamentally different solutions to the problem.


Thx again all, you guys are awesome