Looking for electric system/combi boiler advice please

[MrM]

First post from me, I am hoping for a little bit of advice from anyone who has had experience of using electricity for their heating needs.

 

In brief, we are currently building an outbuilding close to our main house which will require heating (total of 5-6 radiators, no more than 20,000 BTU total and unlikely to all be needed at once) and a bathroom (shower only). This outbuilding will house a guest bedroom, a small gym/exercise space and a home office. Our main house has a standard U6 gas meter.  The run from the meter to where we would look to site a boiler is about 35m and we have been told we would need to upgrade our meter which we have ruled out on cost. We cannot easily store LPG. As a wildcard I looked into air to air heat pumps, which look interesting, but very expensive to install and would not solve our hot water situation. We live in a conservation area so installing solar panels on the roof is a no go. It looks like electricity is really our only viable option and I plan to install a wet CH system and I am looking to use a Honeywell Evohome thermostat solution and so only heat individual rooms as needed to run as efficiently as possible.

 

Whilst I am not too concerned about running costs, due to level of insulation and the relative infrequent use of the building we need to be as economical as possible. I would anticipate we will use the office space 4 days a week, the gym space three times a week and the guest bedroom on an adhoc basis. My main concern is the heating of hot water for the bathroom as this will only be needed on demand. As I see it we have 2 options, a heat only boiler twinned with an unvented cylinder, or an electric combi. I am concerned that we will incur costs heating and storing water and not needing it if we install an unvented cylinder, but this would give us reasonable pressure in a shower. I realise the ecombi is relatively new technology and the advice I have been given is to stick with the more tried and tested solution.

As such I am keen to hear about peoples real life experiences with ecombis. I have been looking into products from EHC and Elnur, which both appear to have some internal hot water storage (for instant demand) which is fine, but what then happens should this store run out? I am hoping to avoid guests having a cold and weak shower if they come to stay with us.

 

Thanks for taking the time to read


 

[ProDave]

For the hot water, consider an instant electric water heater, or a low volume stored water heater, often referred to as "under sink" units.  These make sense for low usage situations so you are not wasting heat with standing heat losses from water you will never use.  

 

And fit the largest power Electric shower you can find. Heat on demand but only when in use.

 

Now you have separated heating from hot water, I really would look at a small monoblock air source heat pump. You can buy one new for about £2K or cheaper if you scour the likes of ebay for a bargain that come up from time to time.  Couple this to under floor heating and you have a very eficcient system.

 

Any half competent plumber and half competent electrcian can connect these for you.  The high prices you have seen are probably from MCS registered companies trying to sell you a system that is eligible to claim the RHI, but often what appears to happen is their prices are over inflated, so your RHI payment barely meets the extra over inflated install price.

[MrM]

Thanks ProDave, if you dont mind I have a few questions. Would you be able to elaborate on the heat pump side of things?  I presume you mean scrapping radiators altogether in favour of a wet underfloor heating system that would always be on? How would this cope in a cold Winter? Do you have an example of a heat pump I can look into?

We are planning on installing vinyl laminate (Amtico/Karndean) in much of the build, with some kind of shock impact rubber flooring in the gym. Would this impact the underfloor heating aspect in your opinion?

 

[scottishjohn]

2 hours ago, MrM said:

Thanks ProDave, if you dont mind I have a few questions. Would you be able to elaborate on the heat pump side of things?  I presume you mean scrapping radiators altogether in favour of a wet underfloor heating system that would always be on? How would this cope in a cold Winter? Do you have an example of a heat pump I can look into?

We are planning on installing vinyl laminate (Amtico/Karndean) in much of the build, with some kind of shock impact rubber flooring in the gym. Would this impact the underfloor heating aspect in your opinion?

 

your rubber floor in gym will be too good an insulator for UFH to work well 

there are special radiators made for use with ASHP -winter is no problem for ASHP in uk as temps never get that low for that long

,or you would have to use twice the area of std type radiators ,as the heat level is only half as much as normal boiler.

if it was me and you have mains gas--then that will always be cheapest option .

 

Edited February 19, 2019 by scottishjohn

[ProDave]

Here is a typical example, the first on I could find from a reputable manufacturer, not necessarily the best or cheapest, just an example. https://www.ebay.co.uk/itm/Samsung-Air-Source-Heat-Pump-5kW/223220316591?epid=19025583729&hash=item33f8f7b9af:g:insAAOSw-pNb4eTC:rk:32:pf:0

 

They work best when you can keep the flow temperature low, say about 40 degrees.  That will work well with under floor heating, but you can still use radiators as long as you buy ones designed specifically to run at a low water temperature.

 

The principle of a heat pump is they extract heat from the air, so for every 1KW of electricity they consume, they will typically deliver 3KW of heat to your room.

[PeterW]

Do you have a floor plan as this isn’t that big and you could get a decent air to air heat pump that would do 99% of this. It would also help with cooling in the summer. The self fit pre filled ones are change of £700. 

 

Electric shower, under tile heating and an electric towel rail sorts the shower room. As @ProDave said - point of use for hot water is the key. 

 

If you did go UFH, then a 5Kw ASHP would be fine - run it at 35c and just change the spacing between the pipes to get increased output. If you’re looking at one of the rubber floors such as the Armstrong ones then it will be no issue as they are only 4mm thick at best. If it’s rubber crumb then it could cause problems unless you go with  100mm pipe spacing. 

[MrM]

Ive attached a floorplan. Ignore any comments re finish and materials as this can change.

Original plan was to split the feed from our U6 gas main. Our meter is approx 12m from the road. This outbuidling is approx 35m from the meter. It was deemed by our engineer that if we tee'd off of the existing connection that we would have insufficient pressure and potentially flow for a boiler in the main house (~30kW) and a small combi in the outbuilding. A preliminary estimate to upgrade to a U16 meter was approx £4k and would mean digging up a mature garden to do so. Likewise a trench from the meter to the outbuilding would be very disruptive. It seems fewer engineers can service U16 meters, so all things considered, for the amount we will heat the outbuilding, we are looking at electric.

Given the original plan was wet CH heating via gas, the obvious step was the same via electric. I spoke to a few local engineers who install ASHP's and received mixed advice, with some saying for the usage, stick to an electric boiler solution. My plan was to install a separate E7 circuit, heat rooms if required before 7am, and same for a short boost of hot water. Then top up either if needed later in the day.

I do have concerns an electric shower wont prove robust and powerful enough for our desire. I also have some issues with how they look and wont fit with our bathroom design particularly well. 

We live in a conservation area, so I cant place numerous condensers outside of the building. I would need to make do with one condenser at the rear for any AHSP solution we were to put in place. The air to air solution is interesting, especially to provide cooling in summer, but when I looked at cost it wasnt cheap (Daikin multi split solution with 5 units was approx £4.5k and plenty of reviewers seemed to run into problems).

 

Above all else I would like a hassle free solution that works with minimal maintenance and I am willing to pay a small premium for this.

 

[MrM]

So after further meetings with our builder and architect we have decided to drop the wet CH idea.

Choice is now electric radiators in each room, or underfloor heating with an ASHP, and aiming to have that heat water in a cylinder too.

My concern is whether UFH is best for our needs. As above, the office and bathroom will be used often, gym and bedroom less so. I dont want to heat the floor unnecessarily, but also dont want it to be cold when we do want to use those rooms, especially the bedroom. Any idea what running costs would be like to keep the building at 16c? Another concern is noise from the condenser, is this particularly bothersome?

Thanks again

[ProDave]

8 minutes ago, MrM said:

Any idea what running costs would be like to keep the building at 16c? Another concern is noise from the condenser, is this particularly bothersome?
 

That depends on insulation and air tightness.  It has cost less than £200 to keep my entire house at 20 degrees all winter.,

 

As long as you get a modern inverter driven ASHP noise will not be an issue. Ours is behind the garage but a small window in the lounge looks out towards it, and we never hear it indoors. 

[MrM]

Thanks ProDave. Being a new build I would be disappointed if insulation and air tightness weren't top notch. The condenser would be in the corner of a garden which we will sue for leisure, the area is approx 20m x 20m. If we were sat in the middle, would the noise be an annoyance do you think?

[scottishjohn]

I went for the ecodan +preplumbed cylinder from them --which does your hot water from the ASHP as well

no doubt others will tell you can do it cheaper  and i would n,t disagree  ,if you are hands on and want to learn all about heat pumpps etc -

-but i went for simplicity and only  I man to call if a problem 

I was on lpg --changing to ASHP and changing nothing else on the old UFH system  

I saved over £1000 per year on running costs--my house is an older TF from the 80,s --not super insulated like a new one you will build 

so yes ASHP will be cheapest and simplest solution   IMHO

 

[Jeremy Harris]

5 minutes ago, MrM said:

Thanks ProDave. Being a new build I would be disappointed if insulation and air tightness weren't top notch. The condenser would be in the corner of a garden which we will sue for leisure, the area is approx 20m x 20m. If we were sat in the middle, would the noise be an annoyance do you think?

 

 

Sadly, many new builds aren't anywhere near as airtight or well insulated as they should be.  Have a read of these two papers:

 

https://www.aecb.net/publications/publication-author/paul-buckingham/

 

https://www.aecb.net/still-taking-disgraceful-approach-build-quality-waving-goodbye-energy-savings/

[epsilonGreedy]

38 minutes ago, ProDave said:

That depends on insulation and air tightness.  It has cost less than £200 to keep my entire house at 20 degrees all winter.,

 

As long as you get a modern inverter driven ASHP noise will not be an issue. Ours is behind the garage but a small window in the lounge looks out towards it, and we never hear it indoors.

 

 

That is an impressive running cost, is there a post where you have documented the insulation element of your build e.g. insulation thickness below your floor screed?

 

Also does your ASHP benefit from a warmer south facing position?

 

In my case I am discovering that my plot is positioned in a three sided couldron about 1 mile square and as a result nighttime temperatures are routinely 2 to 3 degree below forecast when there is little wind but conversely the couldron heats up quickly which means Swmbo is currently sitting out in the garden reading a book at the end of February. The ideal location for the ASHP is on a north facing wall.

[ProDave]

59 minutes ago, MrM said:

Thanks ProDave. Being a new build I would be disappointed if insulation and air tightness weren't top notch. The condenser would be in the corner of a garden which we will sue for leisure, the area is approx 20m x 20m. If we were sat in the middle, would the noise be an annoyance do you think?

When the weather is right for sitting in the garden, I doubt the heat pump will be on?

 

The noise might bother you but so will the blast of cold air coming from it.

[ProDave]

39 minutes ago, epsilonGreedy said:

 

That is an impressive running cost, is there a post where you have documented the insulation element of your build e.g. insulation thickness below your floor screed?

 

Also does your ASHP benefit from a warmer south facing position?

 

In my case I am discovering that my plot is positioned in a three sided couldron about 1 mile square and as a result nighttime temperatures are routinely 2 to 3 degree below forecast when there is little wind but conversely the couldron heats up quickly which means Swmbo is currently sitting out in the garden reading a book at the end of February. The ideal location for the ASHP is on a north facing wall.

Suspended timber floor, 300mm Frsmetherm 35 between joists (JJI I beam) then UFH then engineered oak floor.

 

Walls, 200mm Frametherm 34 between frame studs, and 100mm wood fibre cladding then render.  Same for the roof but tiles not render.

 

U values all around 0.14, just about passable for a Passive House perhaps.  3G windows and good airtightness and mvhr.

 

We are in a valley, the ones they mention in the weather forecast "could be colder in some sheltered Highland Glens"  That is us.  In winter with no wind it gets cold, record low this year was -14, and not above zero in the day, but the cold spell only lasted 3 weeks this year.

 

The winter has been mild this year, nothing compared to last year. As they pointed out on the weather yesterday, this time last year we were dealing with the "beast from the East" and struggling to stay warm in the caravan.  This year I am wondering how long before we need the lawnmower.

 

I hope those heating costs will go down. Once the sun room is done, that should be a good heat collector on sunny winter days. With it just boarded up at the moment the kitchen / diner does not get any solar gain until very late in the day.

[MrM]

Thanks for your comments, all very helpful. In warm weather I guess the pump wouldnt be on to heat the UFH, but might be on at some time if we were to heat hot water using it. I'd like to learn more about the hot water side of things, please forgive me if these are basic questions. What size heat pump am I likely to need to cater for UFH and to heat hot water in a cylinder?  What kind of temp should I look to heat hot water to in a cylinder (excluding any one off immersion boost to kill off legionella) and thus what size cylinder to cater for a shower for 2 people? Any idea how long I should expect for the cylinder to heat to the recommended temp? 

Thanks again

[scottishjohn]

preplumbed mitsubishi clyinder and controller has all that covered -heats up water every now and then hotter than normal ,aslo has an immersion in as well 

it has all pumps on it etc --a good package -go look at it 

[epsilonGreedy]

43 minutes ago, ProDave said:

This year I am wondering how long before we need the lawnmower.

 

 

Lawn mowers have been buzzing in my corner of Lincolnshire for a week or more, mine was in action Sunday afternoon.

[ProDave]

3 hours ago, MrM said:

Thanks for your comments, all very helpful. In warm weather I guess the pump wouldnt be on to heat the UFH, but might be on at some time if we were to heat hot water using it. I'd like to learn more about the hot water side of things, please forgive me if these are basic questions. What size heat pump am I likely to need to cater for UFH and to heat hot water in a cylinder?  What kind of temp should I look to heat hot water to in a cylinder (excluding any one off immersion boost to kill off legionella) and thus what size cylinder to cater for a shower for 2 people? Any idea how long I should expect for the cylinder to heat to the recommended temp? 

Thanks again

5KW ASHP is heating my whole house and DHW

 

I have an unvented cylinder, with a high capacity heat input coil designed for a heat pump.  I heat the HW to 48 degrees with the heat pump. I have a 300L cylinder which is just enough, but there have been a couple of ran out of hot water incidents, so I now have a modulating in line 10KW electric heater that will take over if the tank runs out as a backup for such events.

 

The way most heat pumps work, they heat hot water or space heating, never both together, and they usually run at a lower temperature when doing space heating.

[MrM]

Thanks for the explanation ProDave.

I think Im sold on the ASHP. I now need to decide on air to air, or air to water. 

Given how I plan to use the rooms, I'm inclined to think air to air would be more suitable to our needs; more responsive if needed at short notice, only on shortly before or when we need it and not all the time like UFH. Would anyone argue otherwise?

Only downside I can see is the bulk of the unit on the wall, and the fact I would need a separate hot water solution?

[MrM]

After much more deliberation I feel Im settled on air to air via multi split line. If it were our main house, UFH would be an obvious choice. Due to the adhoc nature of how we will use it, air to air seems to offer a bit more flexibility and responsiveness and the benefit of cooling in the summer would be a bonus. The main penalty is losing the DHW heating. A Daikin system has been recommend and will look to pursue that line, 8.5kW heat pump with either Emura or Stylish wall units.

 

To anyone who has fitted a multi line system, is there anything specific I should bear in mind when thinking about design and placement? I have been recommended to put the units themselves above doors, since that area is somewhat dead space and will not be blowing air directly onto anyone. With regards to piping, anything specific to consider there? Many thanks

[Thedreamer]

On 26/02/2019 at 12:18, ProDave said:

Suspended timber floor, 300mm Frsmetherm 35 between joists (JJI I beam) then UFH then engineered oak floor.

 

Walls, 200mm Frametherm 34 between frame studs, and 100mm wood fibre cladding then render.  Same for the roof but tiles not render.

 

U values all around 0.14, just about passable for a Passive House perhaps.  3G windows and good airtightness and mvhr.

 

We are in a valley, the ones they mention in the weather forecast "could be colder in some sheltered Highland Glens"  That is us.  In winter with no wind it gets cold, record low this year was -14, and not above zero in the day, but the cold spell only lasted 3 weeks this year.

 

The winter has been mild this year, nothing compared to last year. As they pointed out on the weather yesterday, this time last year we were dealing with the "beast from the East" and struggling to stay warm in the caravan.  This year I am wondering how long before we need the lawnmower.

 

I hope those heating costs will go down. Once the sun room is done, that should be a good heat collector on sunny winter days. With it just boarded up at the moment the kitchen / diner does not get any solar gain until very late in the day.

 

Does Frametherm 34 exist, or did it previously exist? I could only ever see 32 or 35? I used 35 140mm for walls and 32 90mm for the floor 

[MrM]

And in the quickest 180 ever, Ive just learned that servicing air con units would be £85/year x 3 plus vat. So £300 a year! Im expecting that to be multiples on what I spend on electricity to service this building each year, which all of a sudden makes it look quite uneconomical!

[Jeremy Harris]

What on earth needs "servicing"?

 

Our ASHP is essentially an air con unit, and all that's required is an annual inspection (which the owner can do in ten minutes) to ensure that the external unit is clean, free from cobwebs etc, plus a functional check.  An air-to-air unit needs, in addition, a check of the drain line and peristaltic pump, but again that's a ten minute DIY job.

[joe90]

I am the same as @ProDave 5Kw ASHP fir all heating and DHW for a 240 sm house, I am going E7 to use lecky at night which will be enough to last the next day. My ASHP was brand new on Ebay for £850 delivered, fitted it myself with help from a plumber.