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2 fan system. Do we really need one??


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Hi all,

We just had a ASHP co come out to measure up or extension and original cottage to quote for an ASHP. By the end of it they have we needed around 8.6, then added a 10% buffer which pushed us above the 9kw LG single fan unit they recommend. The 12kw model they recommend is pretty large and a 2 fan system. It is meant to be attached just to side of cottage and I think it is just 2 big visually to fit in there.

 

the extension is around 60sqm and the entire cottage will be 110sqm when complete. I've seen several rather large houses not far from here fitted with a 9kw system by the same company so wondering how such a small cottage, in comparison to some of these large, double story houses, requires such a big system.

 

Can anyone here point me in the direction of some info where I can get myself up to speed with it all please. The ASHP will be supplying UFH and Hot water and the calcs allowed for a 300l water tank.

 

Thanks in advance.

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Is the cottage being renovated, do you know what the U-values of the various walls / roof / floor etc will be? Possibly the houses where you've seen smaller systems are new-build (or newer-build) and better insulated than your cottage? It's really the level of insulation rather than the size of the property (roughly speaking) that makes the difference to the size of the heat source required.

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10 minutes ago, andyscotland said:

Is the cottage being renovated, do you know what the U-values of the various walls / roof / floor etc will be? Possibly the houses where you've seen smaller systems are new-build (or newer-build) and better insulated than your cottage? It's really the level of insulation rather than the size of the property (roughly speaking) that makes the difference to the size of the heat source required.

Thanks Andy, makes sense re not the size that counts (perhaps that really is true :))

 

Appreciate the feedback. We've actually gutted the existing cottage. It is an old stone wall cottage. Walls about 700mm thick with an outer and inner skin of stone and rubble in between. The roof is slate and felt. No insulation now but I'm putting in 100mm or 120mm of PIR boards in the area where ceiling will be vaulted. Other bits with flat ceiling will have 300mm rockwool type insulation bats. All of it is an existing concrete slab with no insulation but I'm adding close to 50mm insulation and then UFH to that section with those over floor UFH board. This entire section in about 55-60 sqm.

 

The new extension is around 60 sqm. Double skin solid concrete block with PIR 70mm in the cavity for insulation. 120mm PIR on top of 150mm concrete slab floor. the UFH and screed around 50mm. only a small part ( 8sqm) will be vaulted ceiling in this bit and again I'll put in 100 or 1220mm insulation. Rest will be flat ceiling at 2.4 again with 300mm rockwool type insulation. Large windows in gable end that face south sw in the extension so will get good solar gain.

 

I know it's tough to ask for numbers on a forum so hoping some links or websites with calcs that folks have use and perhaps recommend. I've tried looking at some of the info mentioned here and spreadsheet but afraid I've never been the sharpest tool in the shed so struggle a bit with keeping up at times with numbers and acromyms etc. We'll get there and it's all a learning curve so just trying to see if any resources available which might help.

 

Thanks again.

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The only way to be SURE is look at a proper SAP assesment to see the actual heating load.

 

This was brought home to me when a house I was wiring recently, a semi detached house, ended up with a 12kW ASHP, in spite of it's identical twin having an 8kW unit. The supplier did their own sums and ignored the SAP.

 

Oh and take a long read of this thread before you buy an LG unit.

 

A lot of the thread is long winded about me working out a control scheme for it. But towards the end of page 1 not the discussion about spurious "CH 14" (low flow) errors which has been a recurring problem, still not completely cured, and I have heard of a few others with the same problem, still not solved.

 

Ask them what they have done to the units since mine was made to solve the spurious CH14 error problem and what assurances they will give to resolve it if yours suffers that issue. and let us know what they say.

 

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10 hours ago, connick159 said:

All of it is an existing concrete slab with no insulation but I'm adding close to 50mm insulation and then UFH to that section with those over floor UFH board. This entire section in about 55-60 sqm.

This will account for a lot of your heat losses.  Because there is little insulation, the UFH will have to run at a higher temperature, which increases the losses to the ground.

You may find you are better off having radiators rather than UFH.

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1 hour ago, Jilly said:

I've been told to have larger than normal radiators, too, in this situation

Yes, because the supply temperature is lower.

They are not magic radiators, all you need is a larger surface area, so two radiators instead of one is the same as one double radiator.

(as you usual it is a bit more complicated as have to have the return temperature correct to)

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On 16/06/2020 at 07:05, SteamyTea said:

This will account for a lot of your heat losses.  Because there is little insulation, the UFH will have to run at a higher temperature, which increases the losses to the ground.

You may find you are better off having radiators rather than UFH.

 

 

So is this basically saying that all the 'overfloor' types of underfloor heating are no good? (due to heat loss down into slab)

 

https://www.wundatrade.co.uk/product-category/home/overfloor-retro-fit-solutions/reftro-fit-floor-heating-kits/

 

Cheers

 

 

Edited by connick159
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10 hours ago, connick159 said:

So is this basically saying that all the 'overfloor' types of underfloor heating are no good? (due to heat loss down into slab)

Not at all.

What i am saying is that the insulation levels need to be better.

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We put down UFH using retrofit 25mm XPS boards. 
 

heats up nice and quick and is actually calling for heat a lot less than our lounge with rads. 
 

Hard to know about heat loss to the floor but we love it, much better with no ugly rads and warm feet. 

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  • 3 weeks later...
8 hours ago, connick159 said:

update: 8 and a bit grand for 9kw LG monobloc system and a 300ltr HW tank.

With installation etc and MCS it comes to just over 12k.

 

Not cheap is it this heating caper!

You will get the Mitsubishi Ecodan and matching tank for less. That's a better more well known unit as well.

 

Nearly 4K for installation confirms my suspicion of MCS companies over charging.  There is at VERY most 1 man week of labour @£200 per day that's an absolute max of £1000 almost certainly less. ask yourself where the other nearly £3K is going and what it is for?

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1 hour ago, ProDave said:

ask yourself where the other nearly £3K is going and what it is for?

On the admin side of the MCS.  It is not cheap to be part of the scheme.

It is a bit like having your new car serviced at the main dealer or Honest John under the arches.

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4 minutes ago, SteamyTea said:

On the admin side of the MCS.  It is not cheap to be part of the scheme.

It is a bit like having your new car serviced at the main dealer or Honest John under the arches.

My point is you really have to do the sums.  MCS install and claim RHI or just buy the kit as cheap as possible and pay a plumber and electrician to fit it with no RHI.

 

Too many times it seems all or most of the RHI payments just end up in the pocket of the MCS installer, which was not the aim of the scheme.

 

A couple of years back now my plumber friend paid £10K to have the 11kW Ecodan ASHP and tank installed by an MCS installer. So the quoted price here seems way over the top.  But quite why my plumber friend did not just install his own beats me. I would have wired it, I was wiring the rest of the house. As it happens I had to go back and alter what they had done as they were not using the call for heat from the UFH manifold.

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6 minutes ago, ProDave said:

My point is you really have to do the sums

That is always the case.

 

7 minutes ago, ProDave said:

MCS install and claim RHI or just buy the kit as cheap as possible and pay a plumber and electrician to fit it with no RHI.

The RHI was really set up so people that were using oil or non-mains gas had a viable alternative.  it was never meant for low energy new builds or renovations.

The idea was that it should be cost neutral, not to make a 'profit', but in doing so it should reduces the overall CO2 emissions.  That final point is often overlooked.

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2 hours ago, ProDave said:

Too many times it seems all or most of the RHI payments just end up in the pocket of the MCS installer, which was not the aim of the scheme.

 

 

My understanding from a friend that's a civil servant in the BEIS is this is pretty much exactly the aim of the scheme.

There won't be mass-adoption of heat-pumps unless there's critical mass of installers nationally, and the public need to have confidence in their ability to design the systems, install them and support them.  And not enough installers are investing in the training needed to do this without this incentive. RHI is clever economics that worked for PV and they're now applying here to, as while it is government funded, they're getting Joe Public to provide the upfront capital, effectively a loan, to provide  installation bonuses to the MCS installer, that the government then pays off over 7 years

 

Edited by joth
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Thanks for all the comments. Appreciate it as always.
 

in terms of running the calcs and seeing if the MCS v Non MCS path is better, how would I go about that without relying on info from the mob attempting to sell me a system?

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21 minutes ago, connick159 said:

Thanks for all the comments. Appreciate it as always.
 

in terms of running the calcs and seeing if the MCS v Non MCS path is better, how would I go about that without relying on info from the mob attempting to sell me a system?

A random search reveals this price list for the Ecodan heat pumps and cylinders https://www.thefloorheatingwarehouse.co.uk/acatalog/Mitsubishi-Ecodan-Standard-Cylinder-with-Heatpump-Packages.html

 

For instance an 11.2kW heat pump and 300L cylinder costs £5169.  Lets assume that excludes VAT but you will get the VAT back.

Say it costs £1000 to employ a plumber and an electrician to install it.

That's a total of £6169

 

That is almost half the price of your "just over £12K" for an MCS install of a 9kW LG plus cylinder.

 

Now, it you think you are likely to get more than £6K back in RHI payments by going for the MCS install then you might consider that worthwhile.   If as I suspect the RHI payments will be less (they are supposed to be based on energy usage which will be low for a passive house standard building) then you might not consider paying that packaged price represents good value.

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Fwiw I just put down a deposit on 8.5kw Ecodan with OSO 300L Geocoil tank for just over £8.5k+VAT installed, Inc all the intermediate pipework, ufh hookup, external groundworks (concrete base), and the usual MCS additions like room by room heatloss calcs, EPC, and industry body guarantee.

This is in the expensive SE England, I'd hope other areas can beat this price.

 

Caveat: nothing actually installed yet! So can't make a positive confirmed recommendation (yet)

 

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  • 2 months later...
On 10/07/2020 at 13:35, joth said:

Fwiw I just put down a deposit on 8.5kw Ecodan with OSO 300L Geocoil tank for just over £8.5k+VAT installed, Inc all the intermediate pipework, ufh hookup, external groundworks (concrete base), and the usual MCS additions like room by room heatloss calcs, EPC, and industry body guarantee.

This is in the expensive SE England, I'd hope other areas can beat this price.

 

Caveat: nothing actually installed yet! So can't make a positive confirmed recommendation (yet)

 

@joth so that was for an MCS install where you'll get RHI? If so, what is your prediction for RHI? Sounds great

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Fwiw - plenty of us on here have hunted around for cheap kit (e.g I bought my ASHP from a company that was going under) and we installed our own. The difference in price covered all my windows and bifold doors. 

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