Determining boiler size from serial number

[Tim+]

We’re looking into getting an ASHP but I’m unsure of the capacity of our current Vaillant ecoMAX pro boiler as all our installation and other manuals are for 18 and 28kW boilers which I believe are the same externally.

There are no easily accessible ID plates but I do have the serial number that’s been copied into the installation guide.

Before I go bothering Vaillant on the phone does anyone know how to ID our boiler? FWIW, ours is a 5 bedroom house from the early 70s so I’m guessing it’s *probably* the 28kW but I could be wrong.

Tim

[The Natural Philosopher]

Punches advice to people lookimg to get an ASHP. Dont. You'll be lucky to get 10KW out of one.,

[Animal]

First, ashp cost more per kWh output than gas, hence insulation is normally fitted at the same time to hide that. 2nd, I would be loathe to size an ashp based on your current boiler rating. Why? Extra boiler capacity costs little, extra ashp capacity doesn't. Oten old boilers were sized wrong. And you should be adding insulation in most situations, which would make current boiler power a bit immaterial. And not only does ashp cost more to run, it also costs more to buy!

[Theo]

Your boiler is almost certainly oversized so the size is irrelevant really. In the depth of winter does it run continuously or does it cycle on and off (assuming you have the heating on for a long time, not running it for an hour here or there)? If it cycles, then it's oversized.

Do a heat loss calculation and that'll tell you what size you actually need.

Assuming you want the ASHP to do hot water too, work out what size cylinder you have / want and then you can calculate the time to heat it with a given size of heat pump.

Theo

(whose ASHP works just fine, for the record. Nice and warm all year round, for less we spent being barely warm on oil)

[John J]

There is a vaillant air source heat pump Facebook group which you would do well to spend some time reading. To achieve similar comfort conditions at reasonable running cost you WILL have to alter your lifestyle. You WILL have to run your radiators at much lower (40 degree) temperatures than with your boiler thus normally requiring swapping out for larger sizes which may also require pipe changes. You will find a massive problem with ongoing maintenance of the external unit refrigerant containing section and discover there are huge numbers of throw it in and run cowboys who somehow have become "registered" with mcs but when push comes to shove don't expect help from them. If you do pursue swapping to a heat pump check out the installation company on trustpilot and believe the bad reviews more than the good ones.

[Spike]

[…]

Is that comparing like for like, such as ‘oil boiler + some insulation’ with ‘ASHP with the same insulation’, or with ‘ASHP + lots of new insulation’?

[The Natural Philosopher]

Same thought occurred to me.

I commissioned my Pi based heating controller and zone thermometers in December, and by fine tuning it to my actual needs I think I have cut about £1000 off the winter heating bill, And feel warmer.

For less than £150 worth of custom designed bits and a week or three of software.

ASHP works if the house is built for it. It almost never works on larger or older properties. Or where winters are exceptionally cold. And, if you are saving money with it at current prices, there was something wrong with whatever it replaced.

[Theo]

Identical amounts of insulation, which is crap tbh - 80/100mm of fibreglass loft insulation, but the loft is only a crawlspace so putting more in would make it impossible to crawl. Redoing that lot with PIR is on the todo list but it's such a PITA to access.

Theo

[Theo]

You'd do well to get an installer who is Heat Geek certified. They know their stuff and you're likely to get an install that is properly designed. The MCS certification is about 'quality' but more of a box ticking exercise rather than teaching people about the fundamentals of good system design.

The Skill Builder Youtube channel is run by a guy who is a heat pump skeptic, and there's an interesting series of videos between him and the guy who runs Heat Geek. The current series has them look at a botched install by a fly by night company, and how Heat Geek came in and worked out what was wrong with the old install (several basic errors). They're now in the process of fixing it.

Playlist (start at the bottom):

Heat Geek also has a lot of handy videos: Theo

[Tim+]

I’ve come around to that idea too. Decided that gas consumption over the year is probably a more useful measure.

Less fussed about water heating. It’s only costing 35p a day on cheap rate power at present. Designing the system around the hot water requirements rather than the house heating needs seems an odd way to do things if one’s interested in optimum efficiency.

That can’t possibly be true. TNP has spoken otherwise. ;-)

Tim

[Tim+]

Precious few of them in Scotland and the nearest “heat geek verified” one hasn’t ever got back to us to quote. Our local heat geek certified fitter quoted over £25,000. Don’t think he wanted the job.

Tim

[Spike]

Thanks for that.

With such a difference in costs and effectiveness between oil and ASHP, I’m tempted to ask what was wrong with the oil-fired set-up!

As regards the loft insulation, could you get a man in to spray-insulate it? I’ll get my coat…

[Theo]

The oil boiler (20yo) was a rusty pile of ***** and died. I didn't know you could weld oil boilers like you weld old cars, but this one had been welded until there was nothing left but rust to weld. The radiators were ancient too.

Also it needed a giant tank in the garden which was a big waste of space.

The ASHP costs less to run and is more comfortable than oil, so no point reinstalling oil.

:-) Spray foam is ok if done right, as they do in the US. Trouble is in the UK we don't do it enough to trust they're doing it right.

It's not helped by the loft insulation being where all the pipes and wires go, so access is needed to them occasionally. At least with PIR you can pull it up if you need access.

One thought is to line the ceilings on the most awkward side with PIR-backed plasterboard, which would cover some dubious Artex and give an extra layer without taking height from the loft. And maybe on the other side put some PIR between the rafters.

Theo

[The Natural Philosopher]

precisely. Oil at the moment is about 65p a litre which equates to around 6.5p/kWh. Even at 4:1 uplift on an ASHP which is a miracle in winter, that's 26p a unit equivalent electricity.

I am suspicious. It sounds like the old 'double glazing saved me thousands' which turned out to actually mean 'having windows that didn't have draughts saved me thousands'

[alan_m]

From what I've seen on both channels with reference to ASHP:-

It helps to fully research the subject of ASHP yourself before you get a company involved to be able to see through much of the BS.

Putting in a ASHP is not simple as a simple boiler swap. Much of an existing system may also have to be replaced or at least fully evaluated before selecting a ASHP.

Watch out for ASHP that are designed for higher temperatures that are maybe considered for 60C DHW. They will not be as efficient, COP wise, as those working at, say, 40C. The salesman will give you the costs associated with running the 40C system but probably not mention what happens to efficiency when the output temperature rise.

Both channels admit that when it comes to systems running at low temperatures the standard of training (and skill level) in the industry is dire.

[Tim+]

Hard to generate your own oil. Electricity from solar panels is a lot easier.

Tim

[The Natural Philosopher]

Harder to generate your won solar panels.

Christ, the green tendency are thicker than two short planks.

[Fredxx]

Isn't there a blog of comparing gas consumption with ASHP needs? I'm sure someone posted a link here a while ago.

And in the summer given the short term firing times and typical cycling of a boiler heating hot water might have significant losses.

I would agree with TNP, and the only way it becomes cheap enough to run is with further insulation.

[Alan Lee]

Where are you? I can recommend two excellent fitters. Heat Geek 'verified' only means they have passed the HG courses, and registered for the website listing. At least one person in the Company has done the course and passed, but, after that HG dont have any say in what they do, or how they work. I'm on that list on their website.

HG Elite is the 'better' installers, who, again, have passed the HG courses, but they also pay HG a monthly fee to be part of the 'elite'. Again, only one person in the company may have done the course, there is a little bit more assurance, as they can lose their status if there are upheld complaints. They are not a Trade Assn., they are promoting good work by heating fitters, and trying to get a better standard of install, but, they cannot inspect every install done by their 'accredited' Companies.

[John J]

Don't expect to generate much from solar during the dull, short, cold days of mid winter when you need the power most. If your oil boiler is suffering the effects of age there are usually several reasonably young oil boilers on selling sites for very reasonable money.