Green Building Forum - Heat Pump Questions

Heat Pump Questions

mitchino — Tue, 13 Jun 2023 11:09:59 +0100

I think our oil fired Worcester Bosch External Combi is on the way out. A replacement including installation would be Â£4500-5000.

I'm wondering whether now is the time to get a heat pump, as it looks like we can apply for grant funding from the Scottish Government of Â£7500 plus another Â£1500 because we are in a rural area.

Initial Questions:

The oil combi is the 25/32 kW model. What size of heat pump would we need?

I assume we would need an air to water heat pump - can the water tank be located outside of the house - we have a lean-to outhouse, can it go in there?

How far from the tank can the heat pump be located, and is this best positioned in a sunny spot with little wind?

The house has 15 radiators, plus two woodburners which we light when we want save oil. We would want keep the radiators, installing underfloor heating would be too much to deal with. If possible we would like to also avoid having to double the size of the radiators. Is there a system that we could get that would just be a straight swap with the oil combi?

Is it a condition of the grant application that the house has to have a certain level of insulation etc? Some parts of the house are well insulated, other areas are not.

As I said, just replacing the oil combi would be up to Â£5000. Roughly, what would be the cost of a heat pump and tank installation before the grant is taken into consideration?

Anyone with recent experience doing something similar?

Heat Pump Questions

Jeff B — Tue, 13 Jun 2023 18:55:33 +0100

Â£5000 sounds like a lot of money to me for a simple replacement of an oil boiler. I paid that for a new oil system boiler (not a combi) and a new bunded oil tank (it was a replacement for a wood pellet system so we had no oil tank) plus associated pipework.

I looked at ASHP but it would have cost about Â£12K and as I had already had RHI for the wood pellet boiler I could not claim that a second time of course. In any case I was very sceptical that an ASHP would be man enough for our system as we also have 15 radiators with 10mm microbore pipework.

I think you will struggle with an ASHP if you are in Scotland and you say that only some of the house is well insulated.

More experienced folk than I will undoubtedly have something to say shortly!

Heat Pump Questions

mitchino — Tue, 13 Jun 2023 20:03:28 +0100

The price to buy the same boiler is Â£3700, so maybe Â£5000 is a little high.

Looks like it's just a leak from a Â£30 component though and the boiler will survive for now - still interested to hear all opinions though. Been reading about high temperature heat pumps which sound like more of a straight swap, though not as efficient and more expensive to run.

Heat Pump Questions

Jeff B — Tue, 13 Jun 2023 21:00:19 +0100

Even at Â£3700 that seems like a very expensive boiler. I realise you want an external version but a quick scan on the web suggests around Â£2500 for a 25kW jobbie.

I bought my new oil boiler as soon as the 7 year RHI period finished on my wood pellet boiler*. This was because I was nervous that HM Gov would suddenly announce a ban on any new installations of oil boilers and I would have been forced to go down the ASHP route.

*The reasons why I gave up on the wood pellet experiment have been well documented elsewhere on the GBF. Basically it was a pain in the backside and it was no surprise really when the manufacturer went bust about half way through the 7 years!

Heat Pump Questions

WillInAberdeen — Tue, 13 Jun 2023 22:00:52 +0100

We had an ASHP in a slightly-insulated stone house up one of Aberdeenshire's scenic hilltops, worked well. It was a 'high temperature' heat pump, a drop in replacement for oil boiler. Have tried to get another in our new location but local installers are too busy and/or I am too fussy about what I want from them!

Looking now, a dozen new rads are actually not that expensive compared to the rest of the system, there is a good chance they will improve the efficiency and save enough energy bills to pay for themselves quickly.

People get hung up on the purchase cost of the system and don't think so much about the running costs, which add up (in our case) to a bigger amount over the lifetime of the boiler. (Edit to clarify: so buying the boiler fuel is more expensive overall than buying the boiler itself, or the electricity for a heatpump.) Though in real terms heating oil is cheaper than it was before covid, it still adds up. How much (Â£) are you spending on oil annually?

https://energy-stats.uk/what-size-heat-pump/

Highly recommend this write-up of how big it should be, but in the end the MCS installer decides that, not the customer. To be MCS certified, it has to be a generously sized heat pump that can make the house very hot on very cold days without additional heat sources.

Heat Pump Questions

Peter_in_Hungary — Tue, 13 Jun 2023 22:43:35 +0100

I am also thinking of changing my CH + DHW boiler for an A2W heat pump. My boiler is a 40kW gasifying wood burner and whilst different from your oil burning combi I think that some of the same principals apply.

My problem was the same - what size heat pump is needed.

FWIW I hold the opinion that any building can be heated with a heat pump - it just needs sizing correctly. If it is not sized correctly it will be more expensive to run than a correctly sized HP. This is not to say that a poorly insulated house won't be expensive to heat, just that if the HP is not properly sized it will be more expensive than otherwise.

So

Having asked a similar question here I came to the conclusion that without knowing what my heat load is it would be impossible to ascertain the correct size HP.

The heat load will be need to be known on a daily basis so that the coldest day can be managed. Determining the heat load was difficult (impossible) with a wood burner by measuring the fuel input. In the same way it will be difficult to determine your daily heat load by measuring the oil used, especially as the DHW comes from the same boiler.

The solution I came up with was to install heat meters on the system and then keep a log of the daily heat demand. My system supplies 2 detached houses (side by side, 2M gap) and provides DHW for both. Each house has a heat meter on the CH. I also noted the daily min /max temps

Not surprisingly the biggest heat load occurred on the coldest day with a heat load of 81kWh and 70kWh respectively.

Advice from here is that a storage tank is used for DHW and some HP hours should be set aside to heat the DHW i.e don't try to heat the DHW at the same time as running the CH.

Also advice from here was to plan to run the HP for long periods rather than blast the house with heat for frequent short periods.

Adding the maximum heat loads together gives a daily load of 151 kWh, which over 18 hours is 8.4 kW / hour. Then apply a safety factor of say 20% gives a HP of 10kW output.

Then comes the radiator sizing. Conventional wisdom says when you go to a HP the rads. will need to be increased in size to account for the lower flow temps. I found this to be correct !!!

I run my system at 60 deg. flow. To test the performance at HP temps. I reduced the flow temp. progressively until the system failed to perform as required. The results were that just adequate performance was achieved with a flow temp of 50 deg. but 45 deg. was insufficient. So bigger rads will be needed with a change to a HP. However I found that I can move the larger rads to replace smaller ones and by shuffling the rads. around I could minimise the number of new rads. needed. (The system has a total of about 18 rads.).

So the conclusion I came to is that to replace my 40kW gasifying wood burner would need a 10kW output heat pump and the radiators will need upgrading to suit.

I will be quite happy if those here who know better take apart my reasoning as needed.

Heat Pump Questions

mitchino — Wed, 14 Jun 2023 09:10:31 +0100

WillInAberdeen, interesting to note that you think running the heat pump is more expensive than running an oil boiler. I'm less enthusiastic about installing a heat pump and all the disruption that goes with it just to end up spending more every year on energy. I reckon we use between 3000 and 4000 litres of oil a year. We can cut down on that significantly by using the woodburners, but quite often we are too busy or lazy to bother!

Heat Pump Questions

Dominic Cooney — Wed, 14 Jun 2023 09:50:23 +0100

Posted By: mitchino15 radiators, plus two woodburners

Your house sounds a similar size to ours and our oil boiler is 30kW IIRC

we got a quote from Kensa for a GSHP which was propsed as 15kW single phase (no 3 pH here)

But it really does come down to the heat loss of the house, we had to get a room-by-room heat loss calculation done and it wasn't easy because of different ages of the building as it had been extended at different times over the last 200 years.

I can send you the quote if it is of any use to you for interest. it was about Â£15k supply only.
We would have to increase radiator sizes as well.

At the moment we have left space in the field for the 5 x slinkies that are required (we did 2 trenches for the barn covnersion)

While we are slowly working our way around the house upgrading the insulation.

Heat Pump Questions

Doubting_Thomas — Wed, 14 Jun 2023 10:10:59 +0100

Can't remember if I posted this elsewhere, but this is a really intuitive design tool where you can input your building size, radiators etc. and they suggest heat pump size and models

https://heatpunk.co.uk/home

Heat Pump Questions

WillInAberdeen — Wed, 14 Jun 2023 11:15:44 +0100

Posted By: mitchinoWillInAberdeen, interesting to note that you think running the heat pump is more expensive than running an oil boile

No sorry, thats not what I meant, the opposite! I wasn't clear enough.

3000l of oil per year is costing about Â£2000/yr, so Â£20k over a ten year lifetime (depending what happens to world oil prices), so much more significant than the purchase cost of the boiler, and more uncertain.

You'd get about 25000 kWh/yr of useful heat out of that oil. To get the same heat with a heat pump would need to buy 8000kWh/yr of electricity, costing Â£10-Â£15k in the long run over 10 years (depending what tariff you are on, and whether electricity prices continue falling with renewables). So maybe Â£5-Â£10k cheaper than the oil bill, depending on future prices.

So is worth spending Â£5-Â£10k extra upfront on a heat pump compared to oil boiler, plus whatever grants.

If you have an EPC for your house, call some installers, they can look up your approx heat demand online and give you a ballpark cost over the phone, if you decide to go further they will come and survey in detail.

A rule of thumb is take your annual energy (25000kWh) and divide by 3000. So you need 8kW of heat. Then round up to the next standard size model, probably 12kW.

Heat Pump Questions

Jeff B — Wed, 14 Jun 2023 18:02:41 +0100

When we first moved into our place (4 bedroom dormer bungalow, detached) we were using 3000 litres of heating oil per year. We then undertook a pretty big insulation programme of work plus draughtproofing. At the same time we changed to a wood pellet system and we found that we used approx 3300kg of pellets per year which is equivalent to approx 1600 litres of oil. We reverted back to oil in September 2021 with a new oil boiler. I calculate that we have used an average of 4.11 litres per day or 1500 litres per 365 days.

I suppose what I am saying is that I would recommend improving insulation before deciding what type of heating system you require and the output of said system - it may be a lot less than you think.

Heat Pump Questions

borpin — Tue, 20 Jun 2023 14:30:21 +0100

The first thing you need is a proper heat loss survey - any supplier that doesn't offer that - walk away.

System design is critical.

Posted By: WillInAberdeenThen round up to the next standard size model, probably 12kW.

Over sizing a HP can be problematic as it often then cannot modulate down and starts cycling. There is an argument for the sizing to be marginal and accept that on the occasional very cold spells, you need some direct heating to augment it.

HeatGeek are getting a really good rep.

Add in proper monitoring (not just the HPs own monitoring) so you can independently monitor the HP and the COP you are getting. Accept that you do need to monitor performance and tweak the settings on the HP to get the best COP; it is not fit and forget.

Do lots of research on the different HPs available. Data Access (API), Modulation, standby power draw, weather compensation etc.

You may also need Planning consent for the HP - that takes time so if the system is on its last legs, you need to get a shift on!

Heat Pump Questions

WillInAberdeen — Tue, 20 Jun 2023 15:12:39 +0100

>>>> "Over sizing a HP can be problematic as it often then cannot modulate down and starts cycling. There is an argument for the sizing to be marginal and accept that on the occasional very cold spells, you need some direct heating to augment it."

I agree, and would also reduce need for new radiators, but that is specifically not allowed by the MCS standard MIS 3005-D.

If your installer is MCS registered then they have to install a bigger heat pump which MCS can guarantee will heat the house toastie warm in all weathers without augmentation - they don't want callbacks that 'the HP doesn't heat our house enough' or cowboy installers cutting corners with weeny heatpumps.

Heat pumps don't need planning consent (they're permitted development), so long as they are MCS compliant (and not listed/conservation area/ etc)

Edit: Just another plug for
https://energy-stats.uk/what-size-heat-pump/
written by one of the leaders in the kind of monitoring/tweaking that Borpin rightly mentioned.
His room-by-room survey said he needed 5.5kW whereas his actual January energy usage was 3.3kW, so seems the heat loss survey method errs towards bigger heatpumps (70% bigger), ours was similar.

Heat Pump Questions

djh — Tue, 20 Jun 2023 17:52:56 +0100

Posted By: WillInAberdeenIf your installer is MCS registered then they have to install a bigger heat pump which MCS can guarantee will heat the house toastie warm in all weathers without augmentation

I wonder if it's possible to find an installer who is MCS-certified who is wise enough to recognize the problem and do a [smaller] non-compliant installation after doing an MCS survey? And if, what are the cost implications?

Heat Pump Questions

Dominic Cooney — Wed, 21 Jun 2023 09:17:39 +0100

Don't know if this helps at all, but with our GSHP (Kensa) I felt like it wasn't quite managing to warm the barn during the very coldest of the cold snap we had last winter. I called them and they talked me through increasing the flow temp from 30 to 35 (it was very easy) for the UFH
This dropped the COP a bit.
Then I put it back to 30 a few weeks later.
So I now feel very much like it is sized correcly and that there is room for coping with extremely cold weather (I think it was minus 9 or something IIRC)

Heat Pump Questions

WillInAberdeen — Wed, 21 Jun 2023 10:35:26 +0100

New heatpumps should do that automatically (called "weather compensation") - they should constantly be seeking the lowest possible flow temperature that is just warm enough for the radiators/ufh to output enough heat for the prevailing weather. New gas boilers may also do this. Low flow temperatures = better efficiency.

They calculate this using an algorithm which the installers call a 'curve'. Much happy geekery is possible, to tweak the best curve for each house, it's not a case of fitting a box with the default settings, hence new skills needed for installers and customers.

As further layers of geekness, you might want the rads to run warmer first thing in the morning to get the house warmed up quickly, then cooler thereafter. Or run warmer during off-peak electricity prices and cooler at other times.

The TRVs on each radiator or UFH loop might have conflicting ideas about how warm that particular rad should be, so some installers like to remove the TRVs so that the weather compensation is fully in control of the whole system. But then sunshine in one side of the house will overheat those rooms, and the EPC assessor will note that TRVs are absent.

I would be happy to retain some smaller radiators and so let the system raise the flow temperature during the coldest days, I would accept a trade off of radiator size against electricity consumption. But again the MCS installers have to comply with standards that discourage this kind of trading off, they have to make the rads big enough so that the flow temperature stays lowish and no subsequent owner complains about electricity consumption.

Heat Pump Questions

WillInAberdeen — Wed, 21 Jun 2023 10:56:37 +0100

Posted By: djhfind an installer who is MCS-certified who is wise enough to recognize the problem and do a [smaller] non-compliant installation

My problem is finding any wise installer at all, the good ones are busy (as they should be!).

The point of tickbox standards such as MCS are to avoid the installer browbeating the customer (or vv) into a noncompliant installation, even if one or both parties 'knows better', there could be a falling out later that brings the whole trade into disrepute (see also: double glazing before FENSA)

Having got themselves certified, they are not keen to do noncompliant work. It's like electricians blindly following the wiring regs even if a particular job could be done better differently, in the long run it works out better to just follow the rules.

So many things like EPCs, PP, grants etc also require a MCS certificate.

My other problem is I have (a little) knowledge about how I want my jobs done, and trades who feel they are selling their expertise will feel I am a difficult customer! Sometimes it's best to just let the trades get on with it, accept what they propose even if gold-plated, and pay up...

Heat Pump Questions

Dominic Cooney — Wed, 21 Jun 2023 11:08:36 +0100

Posted By: WillInAberdeen"weather compensation"

it did come with a sensor for that as standard, but I didn't want the plastic box on the outside of my barn and also didn't want to run the cable. So I am the weather compensator!

Heat Pump Questions

WillInAberdeen — Wed, 21 Jun 2023 13:41:29 +0100

"Intelligent weather compensation!" - I like it!

The new ones are internet connected so it should theoretically be possible for the installer or manufacturer (or even a clever third party company) to access it remotely, review the operating data and tweak the settings, possibly as part of a service contract, and using tomorrow's internet weather forecast instead of today's temperature measurements from the plastic wall box. I don't know if this is happening in practice yet!

Heat Pump Questions

bhommels — Wed, 21 Jun 2023 14:14:11 +0100

Posted By: WillInAberdeen... and using tomorrow's internet weather forecast instead of today's temperature measurements from the plastic wall box. I don't know if this is happening in practice yet!

For one of the more front running brands it surely doesn't. They have a WiFi breakout box but it does not do much aside from error reporting and enabling the user to set the temperature from their phone app.
The Nest thermostat has been looking up temperatures instead of measuring itself since version 1.

Internet lookup of weather forecasts could enable weather controllers to look ahead and adapt the heating regime to avoid over- or undershoots for buildings that are slow to react, think high thermal mass and/or well insulated...

Heat Pump Questions

gustyturbine — Thu, 22 Jun 2023 17:08:16 +0100

I have a GSHP in a 10 year old property. I also had a hybrid car that we charged fairly often. Our electricity bills came in around Â£500 per month. Family of 5, LED's everywhere. Efficient house. I'm considering a HP in my next house but I'm also considering oil. Mainly as the cost of GSHP's seems high with no RHI currently and I think an ASHP on the coast might corrode. I'm wondering if PV during the summer for electric and hot water plus oil for the winter might be a better way to go currently. I'm fitting MVHR. One thing to note. We fitted UFH downstairs. It works well with tiles etc but a low tog underlay and carpet kills UFH. I wouldn't make that mistake again. My wife insisted on carpet in the lounge so we tend to use the log burner only in there now.

Heat Pump Questions

borpin — Sun, 25 Jun 2023 11:41:31 +0100

Posted By: WillInAberdeenbut that is specifically not allowed by the MCS standard MIS 3005-D.

MCS is a pile of stinking excrement.

Posted By: WillInAberdeenHeat pumps don't need planning consent

In Scotland, perhaps, but in E&W they do (usually).

Posted By: WillInAberdeenand the EPC assessor will note that TRVs are absent.

Better to simply open wide (or fit Wi-Fi ones that can adjust).

Personally, I'd always fit the HP to a tank so heating the tank is independent of the house heat demand. You can also then manage the return flow temp more accurately. Then take off the tank for the heating demand.

Heat Pump Questions

owlman — Sun, 25 Jun 2023 16:45:42 +0100

Posted By: borpin

Posted By: WillInAberdeenHeat pumps don't need planning consent
>In Scotland, perhaps, but in E&W they do (usually).

I was under the impression that all heat pumps were considered permitted development with only a few exceptions.

Heat Pump Questions

djh — Sun, 25 Jun 2023 20:22:33 +0100

https://www.planningportal.co.uk/permission/common-projects/heat-pumps/planning-permission-air-source-heat-pump/

Heat Pump Questions

Simon Still — Tue, 27 Jun 2023 10:53:18 +0100

Posted By: Dominic Cooney
Posted By: WillInAberdeen"weather compensation"

it did come with a sensor for that as standard, but I didn't want the plastic box on the outside of my barn and also didn't want to run the cable. So I am the weather compensator!

Really? It's just an outdoor thermometer and I think ours is less than 20cm square. Should be in a location that doesn't get direct sun and theres no reason you couldn't clad it in the same material as the outside of your barn so long as it still had reasonable airflow. That seems a poor decision - can you retrofit?

Heat Pump Questions

Simon Still — Tue, 27 Jun 2023 10:56:48 +0100

Posted By: bhommelsFor one of the more front running brands it surely doesn't. They have a WiFi breakout box but it does not do much aside from error reporting and enabling the user to set the temperature from their phone app.
The Nest thermostat has been looking up temperatures instead of measuring itself since version 1.

Internet lookup of weather forecasts could enable weather controllers to look ahead and adapt the heating regime to avoid over- or undershoots for buildings that are slow to react, think high thermal mass and/or well insulated...

This is true, but local temperatures can still vary by a few degrees (enough to throw out a heating curve). I'm sometimes surprised at the temperature difference between forecast temp and the readings my boilers weather comp is reading (checked also against another outdoor thermometer that has a display in the house - living in a house that's a constant temperature through winter I find I have to check outdoor temp when deciding what to wear if leaving the house )

Heat Pump Questions

Simon Still — Tue, 27 Jun 2023 10:58:37 +0100

Posted By: owlmanI was under the impression that all heat pumps were considered permitted development with only a few exceptions.

A friend renovating a 60's build in Surrey was told council very down on ASHP due to very quiet location and proximity of other houses. I was dubious but visiting his site I can see it could be annoying.

Heat Pump Questions

Dominic Cooney — Wed, 28 Jun 2023 12:35:04 +0100

Posted By: Simon StillReally? It's just an outdoor thermometer and I think ours is less than 20cm square.

Unfortunately yes.
The box is small, discreet, grey plastic. The barn is stone.
There are no cables, plastic pipes, antennas, or any other thingamajigs on the outside. Only Galvanised guttering & downpipes. Roof windows are frameless, flush-fitting. Windows and doors are painted timber.

OCD

Heat Pump Questions

Simon Still — Thu, 29 Jun 2023 10:00:52 +0100

Posted By: Dominic Cooney
Posted By: Simon StillReally? It's just an outdoor thermometer and I think ours is less than 20cm square.

Unfortunately yes.
The box is small, discreet, grey plastic. The barn is stone.
There are no cables, plastic pipes, antennas, or any other thingamajigs on the outside. Only Galvanised guttering & downpipes. Roof windows are frameless, flush-fitting. Windows and doors are painted timber.

OCD

I'm fully with you on the OCD cleanliness but at some point functionality should trump aesthetics - surely there must be some way it could have been hidden?

cable directly behind box, box behind gutter or downpipe.

A fake bird box if all else failed...

Heat Pump Questions

Dominic Cooney — Thu, 29 Jun 2023 10:24:42 +0100

Not really on the north gable end. The gutters & downpipes are on the east and west sides of the barn.