What's the case for not getting an ASHP?

[kentar]

My boiler has died and I'm able to get a new ASHP installed via government grant. I have few concerns and i'd like some advice.

My property is early 1900's solid wall construction. The loft has been insulated up to standard 10 years ago. New UPVC double glazing was fitted less than 5 years ago. The heating system is a mixture of new, old and really old. All pipe runs to the rads are 15mm, likely branching off a 22mm main (unverified).

 

Firstly, everyone's telling me not to. Only one person I know has had one. I don't have any details about his system or installation, but he moved into a new house which had one and found it to be unsuitable because it was taking too long to heat the water after the DHW cylinder had emptied and meant having more than one consecutive shower was not possible. It was therefore replaced with a gas boiler.

 

A couple of other concerns of mine are placement and noise. I'd prefer to mount mine high up on the wall against my house, as close as possible to the hot water cylinder on the first floor. This will be around 2m from my neighbours house. Is this possible? How noisy will it be?

If it's not doable, can I have it placed at the end of the garden, around 20m away from the existing boiler? The boiler currently resides in the kitchen, with the hot water cylinder directly above it.

 

Thirdly, heatgeek accredited installations are supposedly regarded as the best. How much of a risk is it using someone not accredited?

 

Are there any other considerations? I'm not interested in saving a few hundred quid a year if it means that an ASHP causes more issues than it solves.

[DamonHD]

My newish heat pump is working fine.  Being short of hot water sounds like a tank sizing problem not a heat pump problem.  It's bad for the planet to install a new fossil boiler.

 

Edited Wednesday at 19:25 by DamonHD

[SteamyTea]

If you are serious about getting an ASHP, first thing you need to know is an accurate figure for your heat losses and domestic hot water.

That will set the minimum size for your ASHP.

Once you know that, you can then start looking at what the physical size, performance and price of the units are.  Some may be too large to be fitted without planning permission (this may be changing).

Chances are you will need to change all your heating system, but you probably would if you went for a low temperature combustion boiler anyway.

 

HeatGeek have the marketing advantage, but doing the calculations is only basic arithmetic.  Finding out what your building thermal properties really are is the hard part. 

Edited Wednesday at 19:26 by SteamyTea

[kentar]

20 minutes ago, DamonHD said:

Being short of hot water sounds like a tank sizing problem not a heat pump problem.  

 

 

Yes to a point, but you can't account for every eventuality. Fitting a 1000l tank in my airing cupboard 'just in case' is not viable.

 

My current tank is 140l. I can drain that in less than 10 mins. Assuming 4 people need a shower, that's 560l. A tank that size is just not going to fit.

Edited Wednesday at 19:49 by kentar

[Dillsue]

24 minutes ago, kentar said:

Thirdly, heatgeek accredited installations are supposedly regarded as the best. How much of a risk is it using someone not accredited?

 

Are there any other considerations? I'm not interested in saving a few hundred quid a year if it means that an ASHP causes more issues than it solves.

If you want to lessen the risk then use a heatgeek outfit. You may or may not find a good HP install outfit but that's likely a bigger risk of things not being right than using a heatgeek outfit.

 

If you want to research and understand more about heat pumps then get your boiler repaired, do your research and get the HP installed next spring

[kentar]

25 minutes ago, SteamyTea said:

If you are serious about getting an ASHP, first thing you need to know is an accurate figure for your heat losses and domestic hot water.

That will set the minimum size for your ASHP.

Once you know that, you can then start looking at what the physical size, performance and price of the units are.  Some may be too large to be fitted without planning permission (this may be changing).

Chances are you will need to change all your heating system, but you probably would if you went for a low temperature combustion boiler anyway.

 

HeatGeek have the marketing advantage, but doing the calculations is only basic arithmetic.  Finding out what your building thermal properties really are is the hard part. 

 

A survey will be carried out to determine that, but none of what you have written concerns me.

[SteamyTea]

3 minutes ago, kentar said:

 

A survey will be carried out to determine that, but none of what you have written concerns me.

Can't help you decide then, sorry.

[JohnMo]

34 minutes ago, kentar said:

I'd prefer to mount mine high up on the wall against my house

That is doable, but I wouldn't, I would be worried about noise/vibration coming though, plus they look ugly on a wall and not easy to access. My heat pump is over 20m from the cylinder its still very efficient during DHW.

 

5 minutes ago, kentar said:

Fitting a 1000l tank

Why would you need that size cylinder. You size the cylinder for the number of bedroom. So 3 bed needs a 210 to 250L, if your a heavy user you could up that to 300L. A 6kW heat pump takes 45 mins to reheat the cylinder. I schedule mine twice per day, some days (today) it hasn't needed to heat, but will reheat later.

 

A gas boiler is about 85% efficient, so it cost about 6p per kWh plus about 15% for the efficiency losses. You also have a standing charge to pay.

 

Main thing with poor performing ASHP installs, is generally the home owner wanting to use the ASHP the same as a gas boiler. Use it running all the time slowly adding heat to the house. 

 

 

[JamesPa]

A properly designed ashp system will heat your house and hot water at least as well as a boiler, probably better (more uniformly both in time and space).  It will be about the same cost to run and will heat the planet 1/4 as much, reducing to zero as the carbon intensity of the grid reduces.  Mine (1930 solid wall house with partial internal wall insulation) is about 20% cheaper to run than my gas boiler and much, much more comfortable;  I did my research and the system is properly designed (which to first order, at least in the majority of cases, means heat pump correctly sized, no external controls/thermostats, no buffer tank (kiss!), heat pump run 24*7 on weather compensation).  With a correctly sized dhw tank you won't run out of water and if you need a rapid boost you can flick on the immersion as well as the ashp.  Really not a problem.

 

However if the system is badly designed you will have issues  That's true of a boiler based system as well, but boilers are more tolerant and the heating industry, with notable exceptions, has become lazy.  As @JohnMosays you will also have issues if you try to operate it like a boiler.

 

Incidentally neither of your placement options sound great, it is worth thinking out of the box on this.

 

I would go along with get your boiler repaired and swap next year having done the research, or, if that isn't feasible, get an installer you can trust not a fly by night grant harvester.  Heat geek is definitely a good start, but there are also many good installers who aren't heat geeks.

 

Finally here is a great place to post quotes/questions for comment.

Edited Wednesday at 20:10 by JamesPa

[JamesPa]

1 hour ago, kentar said:

with the hot water cylinder directly above it.

If you already have a hot water cylinder then you have information from which you can work out your needs.  

 

44 minutes ago, kentar said:

Fitting a 1000l tank in my airing cupboard 'just in case' is not viable.

Unless your current hot water cylinder is 500l plus, which as it sits above the boiler is rather unlikely, you don't need to do this!

 

1 hour ago, kentar said:

Firstly, everyone's telling me not to.

 

Most likely because they believe the nonsense they read in a certain section of the press, which is pumping out misinformation (on a whole host of subjects) in support of vested commercial interests and a certain part of the political spectrum. 

 

Personally I view with scepticism anything I read in the press or hear in most of the 'media'.  There are too many vested interests with too much influence to trust anything which isn't verifiable as a minimum by reference to an outlet with the opposite leanings.

Edited Wednesday at 20:31 by JamesPa

[marshian]

2 hours ago, kentar said:

 

Yes to a point, but you can't account for every eventuality. Fitting a 1000l tank in my airing cupboard 'just in case' is not viable.

 

My current tank is 140l. I can drain that in less than 10 mins. Assuming 4 people need a shower, that's 560l. A tank that size is just not going to fit.

 

What temp are you currently heating it to?

 

Most HW uses are blended 60 deg water with 20 deg water at a 50/50 mix gives shower temp water

 

If you can use 140L in 10 mins that's 280 Litres of shower temp water and 28 Litres per min (assuming multiple simultaneous showers)

 

For clarification 2 people living in one house - 115 Litre tank heated to 50 Deg once a day and that's 2 showers each per day or one long hot bath so I'm think your water usage is quite high

[kentar]

22 minutes ago, marshian said:

 

What temp are you currently heating it to?

 

Most HW uses are blended 60 deg water with 20 deg water at a 50/50 mix gives shower temp water

 

If you can use 140L in 10 mins that's 280 Litres of shower temp water and 28 Litres per min (assuming multiple simultaneous showers)

 

For clarification 2 people living in one house - 115 Litre tank heated to 50 Deg once a day and that's 2 showers each per day or one long hot bath so I'm think your water usage is quite high

 

60c I believe. I'm not sure what the blend ratio of hot to cold is. I've got the mixer knob set so the temp I like is in the middle.

 

The fact is, I can empty a 140l tank quite easily. It's pointless questioning or criticising how much water I use. I'm going to use it regardless.

[kentar]

2 hours ago, JamesPa said:

If you already have a hot water cylinder then you have information from which you can work out your needs.  

 

Unless your current hot water cylinder is 500l plus, which as it sits above the boiler is rather unlikely, you don't need to do this!

 

 

My requirement is that 4 people should be able to shower consecutively. My current hot water cylinder does not alllow for this and will be upsized. I can't however, fit a 500l cylinder. So I have make a reasoned decision and live with any shortcomings.

 

Now my question is how long will a ASHP take to reheat a cylinder compared to a gas boiler?

My opinion is that the gas boiler will do it quicker, based on the opinion of someone I know having one, and subsequently replacing it with a gas boiler due to it not heating water quickly enough. As I stated, I do not know the ins and outs of his installation. This is why I'm here, to gather further information from people who may be able to help me make an informed choice.

[MikeSharp01]

6 hours ago, kentar said:

Now my question is how long will a ASHP take to reheat a cylinder compared to a gas boiler?

This depends on a number of factors: The size of ASHP, the area of the heating coil in the tank - the bigger the better, and what you set the flow temperature from the pump for the water heating cycle.

[JamesPa]

 

8 hours ago, kentar said:

My requirement is that 4 people should be able to shower consecutively. My current hot water cylinder does not alllow for this and will be upsized. I can't however, fit a 500l cylinder. So I have make a reasoned decision and live with any shortcomings.

 

4 showers at what rate (20l/min, 10l/min?) and for how long.  The calculation isn't difficult once these parameters are known.

 

Even with a boiler you aren't going to be doing much reheating during the time it takes to shower, so reheat time is of secondary importance what matters primarily is tank size and temperature 

Edited 19 hours ago by JamesPa

[JamesPa]

8 hours ago, kentar said:

As I stated, I do not know the ins and outs of his installation. This is why I'm here, to gather further information from people who may be able to help me make an informed choice.

Based on some of what you say above I do wonder if this is truly the case, or whether (perhaps subconsciously) you are really trying to find evidence to support the decision you have already made (again perhaps subconsciously).  

 

Are you truly undecided?  If you want an ashp to work for you it will, if you don't want it to work for you it probably won't!

Edited 18 hours ago by JamesPa

[Roger440]

Based on your comments, id say fit an electric shower. Then you can have a shower all day if you want. Problem solved.

 

Meanwhile, back to your boiler.

 

Yes, you can fit an ASHP and yes it will be ok. In theory.

 

The reality out in the realkworld is that its likely not to be well installed. People on here are not a good cross section of the population at large, as they are invariably much better informed and likely to take a very active part in the decisions on what gets installed. And because they understand, are willing and able to adapt their behaviours to suit the way an ASHP works. Again, most of the population dont and wont. They expect to turn the thermostat and the rads to be toasty hot 10 mins later.

 

If you can/want to do all that, thats fine. If not, id just nail another gas boiler in. Cheap and simple. There are no downside risks to that.

 

With ASHP there are lots of downside risks unless you are actively involved.

 

[JamesPa]

10 minutes ago, Roger440 said:

Based on your comments, id say fit an electric shower. Then you can have a shower all day if you want. Problem solved.

 

Except that an electric shower, sofaik, will do max 10l/min.  We still don't know if OP 'requires' 20l/min (some people do apparently, no idea why!).  He needs to answer the questions I posed above about length and rate before a design can be done.  

Edited 18 hours ago by JamesPa

[Roger440]

Just now, JamesPa said:

Except that an electric shower, sofaik, will do max 10l/min.  We still don't know if OP 'requires' 20l/min (some do apparently).  He needs to answer the questions I posed above about length and rate before a design can be done.  

 

Agreed. But the source of heat doesnt actually matter if the tank cant be any bigger, its still not going to deliver 4 consecutive showers.

[JamesPa]

Just now, Roger440 said:

 

Agreed. But the source of heat doesnt actually matter if the tank cant be any bigger, its still not going to deliver 4 consecutive showers.

Agreed.  I think he implied that he was going to get a bigger tank anyway though (irrespective of the source of heat).

 

Best approach would be waste heat recovery, but that requires access to the shower drain and some plumbing work.  It would double the amount of showers he could get from any given size of tank though, and reduce his DHW bills by a corresponding amount.

[marshian]

8 minutes ago, Roger440 said:

 

Agreed. But the source of heat doesnt actually matter if the tank cant be any bigger, its still not going to deliver 4 consecutive showers.

He want 4 simultaneous showers  - so he will need a bigger tank heated to a higher temp so he doesn’t run out of water during showering - urban plumbers did an install where the gas boiler was set up on HW priority and a small tank was mated to a gas boiler and it could reheat HW as fast as it was being used - like a huge storage combi but without the peak flow limitations of a combi (the biggest of which can’t supply 4 simultaneous showers)

 

Thats the way I would go in this situation

[JamesPa]

16 minutes ago, marshian said:

He want 4 simultaneous showers  - so he will need a bigger tank heated to a higher temp so he doesn’t run out of water during showering - urban plumbers did an install where the gas boiler was set up on HW priority and a small tank was mated to a gas boiler and it could reheat HW as fast as it was being used - like a huge storage combi but without the peak flow limitations of a combi (the biggest of which can’t supply 4 simultaneous showers)

 

Thats the way I would go in this situation

Complex though and uses a lot of space. 

 

Personally I'd just amend my routine to be more reasonable in my demands, but I know that's an unpopular view, even though it's the only one consistent with any faint degree of sustainability.

 

Four showers in quick succession (often, perhaps not in this case, for a long time at 20l/min) is the archetypal first world problem!

Edited 17 hours ago by JamesPa

[marshian]

1 hour ago, JamesPa said:

Complex though and uses a lot of space. 

It all fitted in a tiny bathroom on DHWP - I thought it was very simple (whilst being bloody clever)

 

 

Edited 16 hours ago by marshian
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[JamesPa]

2 hours ago, marshian said:

It all fitted in a tiny bathroom on DHWP - I thought it was very simple (whilst being bloody clever)

 

 

Fairy nuff.

[marshian]

11 minutes ago, JamesPa said:

Fairy nuff.

Sorry it wasn’t a criticism of your comment - I think you made a valid point that it’s easy to make solving a problem complicated

 

Urban Plumbers  videos are often good for “out of the box” approaches to heating/hot water solutions to specific customer needs that aren’t complicated which is why I’ve watched every single one he has done - I remembered this one so linked to it.