Which heating and hot water solution(s) in 2024?

[Jane W]

I'm considering how to supply heating and hot water to a 150 sq m 1 3/4 storey self build. I'm going round in circles. I can't get past the cost effectiveness of a gas boiler and the ability to provide instant heat.

Capital cost is definitely a primary driver in the decision.

At the same time eco friendly options appeal because it will future proof the build and help getting planning I think.

Could anyone share what they are planning or have had installed recently. I'm interested in the complete system you have chosen for heating and hot water solutions and why, particularly where capital costs were a primary consideration. 

Thanks 

 

[Dave Jones]

cheapest is definably solar, heat pump and an eddi diverter.

 

As for capital cost, buy a 5k kitchen instead of a 25k kitchen.

 

Same reasoning.

[TonyT]

Or plumb for a heat pump, size radiators for a heat pump, fot UV cylinder as normal and get a viesmann boiler with weather comp, 

 

 

[JohnMo]

16 minutes ago, Jane W said:

I'm considering how to supply heating and hot water to a 150 sq m 1 3/4 storey self build. I'm going round in circles. I can't get past the cost effectiveness of a gas boiler and the ability to provide instant heat.

Capital cost is definitely a primary driver in the decision.

At the same time eco friendly options appeal because it will future proof the build and help getting planning I think.

Could anyone share what they are planning or have had installed recently. I'm interested in the complete system you have chosen for heating and hot water solutions and why, particularly where capital costs were a primary consideration. 

Thanks 

 

We started with a combi boiler, driving UFH, thought nice, easy, cost effective. But getting a big gas boiler to work well in a low energy house isn't easy. They just short cycle, using way more gas than they should. Eventually got it working well. But swopped it last year for an ASHP, all self funded.

 

Doing it again, ASHP every time, 3m2 coil UVC for hot water. House heated as a single zone.

 

Three ways to heat

Fan coils not the cheapest option, but good for cooling and heating

 

Big radiators run on weather compensation 

 

or UFH on the ground floor and any upstairs bathrooms. Add provision for electric panel heaters in bedrooms, just in case you need them. If doing UFH do a 100mm thick screed and charge on a cheap tariff the same as a storage heater, or thin screed and run on weather compensation.

 

MCS grant scheme should be the cheapest, but just seems a rip off get quick scheme for installers.

 

From everything I've seen Panasonic ASHP seems very good, something like a 200L cylinder, and heat emitters is all you need. £4-5k all in, plus install, and there is nothing complicated.

 

Insulation and ventilation will have an impact on heat source sizing.

 

29 minutes ago, Dave Jones said:

buy a 5k kitchen instead of a 25k kitchen.

Best advice I have seen. We have done many kitchens in many houses, back in 1999 we spent 25k on a kitchen, latest one in 2022 was about £7k and way nicer.

[Dave Jones]

we have panasonic fancoil units in the bedrooms, mainly for cooling use. yet to use them as its too hot upstairs already with a flow temp of 25c to the slab.

 

Plate heat exchanger while a bit more money are much more efficient than in tank coils and allows the use of multiple bog standard cheap cylinders.

[Jane W]

3 hours ago, Dave Jones said:

cheapest is definably solar, heat pump and an eddi diverter.

 

As for capital cost, buy a 5k kitchen instead of a 25k kitchen.

 

Same reasoning.

Definitely agree with kitchen, this will be 3rd time buying a kitchen and budget getting lower each time!

[Jane W]

Just now, Jane W said:

Definitely agree with kitchen, this will be 3rd time buying a kitchen and budget getting lower each time!

Heard good and bad about Eddies, had solar pv on previous house with FIT tariff,  do you think they are worth the capital outlay now with cheap overnight tariffs?

[Jane W]

46 minutes ago, Dave Jones said:

Plate heat exchanger while a bit more money are much more efficient than in tank coils and allows the use of multiple bog standard cheap cylinders.

I haven't looked into these or fan coils tbh, what considerations made you go that route?

[JohnMo]

1 minute ago, Jane W said:

do you think they are worth the capital outlay now with cheap overnight

Really depends on what the supplier pays you per kWh export. If you have a smart meter you could get 15p if you don't or live in a area where they don't function it's 4p. So even then it's best to self consume as much as possible.

[Jane W]

3 hours ago, TonyT said:

Or plumb for a heat pump, size radiators for a heat pump, fot UV cylinder as normal and get a viesmann boiler with weather comp, 

 

 

Because you think I'll end up with a heat pump anyway?

Looked at Viessman micro chp boiler for previous house but why Viessman in this case (I'm a bit clueless!)

[Jane W]

3 hours ago, JohnMo said:

We started with a combi boiler, driving UFH, thought nice, easy, cost effective.

This is exactly what I had in mind.

So if going with an ashp if you were to do it again how would you do dhw? Do you still use gas atm or have you installed a cylinder?

[JohnMo]

6 minutes ago, Jane W said:

again how would you do dhw?

Unvented cylinder, heated by ASHP to 47 to 50 degs.

 

 

[Jane W]

1 hour ago, JohnMo said:

1 hour ago, Jane W said:

 

Unvented cylinder, heated by ASHP to 47 to 50 degs.

 

 

And then topped up with immersion to prevent the bugs?

[Conor]

6 minutes ago, Jane W said:

And then topped up with immersion to prevent the bugs?

Not needed unless you are on an untreated private supply. 45c is fine for how water of you have a big enough tank. 

[JohnMo]

13 minutes ago, Jane W said:

And then topped up with immersion to prevent the bugs?

As above no. If you specify a suitably size UVC and water is sitting for weeks. If the contents of the cylinder don't get used, then there maybe a case to heat once a week to 60 Deg or if you someone in the house with a suppressed immune system. There are two of us in the house and we have a 210L cylinder it gets heated to 50 usually twice a day.

 

If mains water, or borehole with suitable treatment system and in a closed system where air, debris etc. cannot get into the system, no contamination can occur.

[JamesPa]

5 hours ago, Dave Jones said:

Plate heat exchanger while a bit more money are much more efficient than in tank coils and allows the use of multiple bog standard cheap cylinders.

I'm interested in this comment.  One ashp installer I am talking to suggests a pump plus phe instead of a large coil in the cylinder.  The cost is no different because it allows you to use a cylinder that doesn't have a coil (£400) as opposed to a heat pump specific cylinder (800+).

 

The arguments for the arrangement seem potentially convincing to me, although there is the noise of the pump to consider.  It also introduces the possibility to put the pump plus phe remote from the cylinder, or retrofit an existing cylinder which has an insufficiently large coil, both of which have applications.

[Jane W]

11 hours ago, JohnMo said:

Really depends on what the supplier pays you per kWh export. If you have a smart meter you could get 15p if you don't or live in a area where they don't function it's 4p. So even then it's best to self consume as much as possible.

I think batteries are probably the way to go with solar Pv and take advantage of low demand electric tariffs from the likes of Octopus energy, but again the upfront cost is very high...

[Iceverge]

I'd rather spend more money on the building fabric than batteries. 

 

More insulation will last forever and a day. 

[Jane W]

6 hours ago, JamesPa said:

One ashp installer I am talking to suggests a pump plus phe instead of a large coil in the cylinder

What are the benefits over a heat pump cylinder given similar initial costs?

[Jane W]

1 minute ago, Iceverge said:

I'd rather spend more money on the building fabric than batteries. 

 

More insulation will last forever and a day. 

Agreed, to a great degree. I thought you were thinking solar pv but I realise now you mean passive solar🤦🏼‍♀️

[Iceverge]

5 minutes ago, Jane W said:

Agreed, to a great degree. I thought you were thinking solar pv but I realise now you mean passive solar🤦🏼‍♀️

 

I'm thinking we may have wires crossed!

 

I would advocate burying any cash into the bits of the house that can't be changed or added easily later. Specifically 

 

MVHR

Airtighness 

Insulation 

Triple Glazing. 

[JamesPa]

10 hours ago, Jane W said:

What are the benefits over a heat pump cylinder given similar initial costs?

Principally that more of the tank is heated so you can have a smaller tank.  Also arguably greater efficiency (see the mixergy blog on this).  You can probably get a smaller approach temperature (different between flow temp and dhw temp) also.  Furthermore the coil isn't taking up space in the cylinder.

 

The other potential advantages are situation dependent and mostly applicable to retrofits.  It can be done as a retrofit to an existing tank which otherwise has an insufficiently large coil, and/or the phe doesn't have to be colocated with the cylinder (I can't actually think of a specific circumstance where this is useful but there is bound to be one!).

 

On the negative side it's more complex and less familiar to plumbers.

 

A couple of heat pump manufacturers cylinders use a phe and pump instead of a coil (Mitsubishi, plus I think Ideal)

Edited March 17 by JamesPa

[JohnMo]

19 minutes ago, JamesPa said:

Also arguably greater efficiency (see the mixergy blog on this). 

https://mixergy.co.uk/news-and-insights/plate-heat-exchanger-vs-coil-the-great-debate/

 

Interesting read, but does generalise with respect coils, making the assumption that all coils are just a single coil.  Most coils are now multiple coils run in parallel, so you could have 4 to 6 separate coils fed from a manifold to make up the coil stack.  It assumes the coil starts a fair way up the cylinder. My nothing special off the shelf cylinder, the coil starts as low down as practical, being just above the immersion. Not as low as the mixergy but not 20% higher as indicated in the text.

 

I do believe the extra heat transfer efficiency. But you have an extra pump in the system also.

 

The bit I find worrying for the real world is this - 4 hours to reheat the cylinder.

 

https://mixergy.co.uk/news-and-insights/real-world-performance-of-mixergy-and-heat-pumps/search

 

[TonyT]

22 hours ago, Jane W said:

Because you think I'll end up with a heat pump anyway?

Looked at Viessman micro chp boiler for previous house but why Viessman in this case (I'm a bit clueless!)

Who know if you will go down the heat pump route, but either system can be designed for low temp radiators, appropriate pipework diameter.

plan pipework routes to make any change over in the future easier

[JohnMo]

1 hour ago, TonyT said:

but why Viessmann 

 

On 16/03/2024 at 11:24, Jane W said:

but why Viessman in this case (I'm a bit clueless!)

Because they have an excellent turndown ratio. By that I mean minimum output which is something like 1.8kW, compared to must which have nearer 6kW for the same boiler rated max output. This helps minimise short cycling which can use lots of gas.

 

Other good things you get with a good boiler are two flow temps one for heating a cylinder and the other for central heating. With gas boilers the lower the return temperature back to boiler the higher the efficiency.

 

Irrespective of heat source chosen I would design the heating system and the hot water the same (unless you want a combi boiler). Heating system design for low flow temps and hot water storage design around a heat pump cylinder with storage temperature of 50 and below. If you go combi, get one that will take preheated water (Atag, Ideal, Intergas to name a few). And read the papers below - been there and it works well.

 

Combi-SuperFlow-White-Paper-v1-2-4.pdfCanetis-SuperFlow-Product-Sheet-WE-050318.pdf