Is an upgrade to unvented worth the cost?

[VentOrUnvent]

This is quite a long post... the gist of it is "is upgrading to unvented worth the extra cost compared to a straight boiler+pump vented upgrade?". There's a couple of other questions thrown in but that's the main thrust. Now some details...


We have a 5 bedroom, 3 bathroom house with good mains pressure (5.5 bar) and good differential pressure (3 bar) - I hope that's the right term to use - i.e. the pressure sustained when the kitchen tap is turned on. Our flow rate is also good at ~22 litres/minute.


Our current system is vented, boiler in the garage, ~120l cylinder in the hallway cupboard. The boiler is old and at 50 BTU is far too small for the house, which was extended a few years back without any upgrade to the heating system. We have all sorts of problems at the moment with rads taking ~90 minutes to start to get lukewarm and want that fixed so we can have a nice warm house quickly. Hot water recovery time is very good - 20 or 30 minutes to have enough hot water for a bath.


We also want to take advantage of technology like the Honeywell EvoHome to selectively and remotely control each room's heating.


We've had 5 heating engineers all recommend upgrading to an unvented system and moving the cylinder to the garage alongside the boiler. This has resulted in quotes of £7k+ (with the Evohome extra on top), with boiler suggestion around 27kwh (based on 14 radiators), cylinder size suggestions from 170-300l.


One heating engineer has suggested redoing the house's pipework into "upstairs" and "downstairs" instead of installing evohome. We've also been told by one person that we absolutely have to rip out all the microbore (and all the disruption that entails). We've also been told be one person that we definitely need an accumulator, the others have said not.


Adding into the cost factor we also have 2 Mira digital pumped showers to that's another £500 replacing those for the unpumped controllers.


We're struggling to know what the "right thing" to do is.


I guess our questions are:


- Is the unvented system really worth the extra cost of installation compared to upgrading the vented system? I understand unvented is "better", but is it £4k better?
- Should we replace microbore day 1, or is that something we should only do later after the system is cleaned and upgraded if we still have problems?
- Is the upstairs/downstairs pipework zoning worth the cost and effort when compared to putting in EvoHome?
- What size cylinder do we really need? We've had such a range of answers we just don't know how to estimate it.
- Do we need an accumulator with that pressure + flow rate?


Apologies for the long post but I appreciate any help you can give.

 

[joni os]

Extending property does not necessarily mean a proportionate increased in heat demand as new standards of insulation make property more thermal efficient.
An old 50 BTU boiler at 70% efficiency is giving no more than 11Kw output and this is undersize but equally 27Kw would seem oversized.
Check the circulation in your radiators by turning half off, the remainder should reach temperature in 15 minutes, if not the problem is circulation, pipework or pump, and with old microbore system I suspect the former.
Adequate sized pipework is essential for an efficient system, start by getting this right.
Vented or unvented your cylinder needs to be 250 litre+.

 

[SimonG]

Unvented all day.

 

[VentOrUnvent]

Unvented all day.

Even with the big price difference? Obviously everyone is telling us that's the best way to go - but we're trying to work out if it's worth spending an extra several thousand quid to:

1) Get rid of tanks (not a big deal, we have LOADS of loft space)
2) Get rid of shower pumps (pretty good, gets rid of noise in the morning)
3) Fill baths quicker (ok saves us 10 minutes 3 times a week).

What have we missed to justify the cost?!

 

[Best]

Unvented shouldn't really cost too much, but depends more on the repositioning from original position of old copper cylinder.
Microbore pipes might be poorly done and too big runs, plus there is a risk your system might have sludge in rads & pipes, but would take a heating engineer to check that out.
It is really up to you, - if you are going to save thousands staying with a gravity water system that you are fairly happy with, then that's fine. But if you are doing major upheaval to your house anyhow, don't do it by half, do the whole thing to modern standards.
It's really how much money you can afford.

 

[Best]

Put it this way, - although a fairly extreme example, - I had to do a large roof space conversion (heating & shower room) and this involved moving & replacing the copper cylinder on ground floor, which customer agreed would be best an unvented unit. It was a no brainer as cheaper to do unvented than run all the extra pipes up into a new attic and cwt etc for a gravity system would have cost a lot but no great water pressure.
When I came to join on to existing heating on ground floor & replace/add a few rads I found the Microbore to be full of treacle like sludge & rads same, plus the pipes were clearly too long runs. Microbore will not work over great distances.
Customer agreed to have me replace all pipes & rads and now has a brilliant fast working heating system & a high pressure water system and really for an extra £2000 I guess. She doesn't regret it and loves her shower

 

[SimonG]

Even with the big price difference? Obviously everyone is telling us that's the best way to go - but we're trying to work out if it's worth spending an extra several thousand quid to:

1) Get rid of tanks (not a big deal, we have LOADS of loft space)
2) Get rid of shower pumps (pretty good, gets rid of noise in the morning)
3) Fill baths quicker (ok saves us 10 minutes 3 times a week).

What have we missed to justify the cost?!

'Everyone is saying its the way to go'.

What else do you need to know?

The only thing I would add is that I wouldnt have the cylinder in the garage. Needs to be close to your main draw offs. Horizontal cylinder in loft space above bathrooms.

 

[joni os]

Doubling the output of your boiler will half the recovery time on your existing cylinder.
If this sorts out your heating you have money to spare for unvented. I suspect your problem is in your pipework and this should be sorted before any cylinder replacement.
The heating engineer who is best to replace your boiler may not be interested or even best suited to rectify pipework in existing occupied property. Do the work in stages

 

[VentOrUnvent]

'Everyone is saying its the way to go'.

What else do you need to know?

Fair question - but as above really, do the benefits warrant the additional costs (moving cylinder, altering pipework, replacing shower controllers)?

I haven't quite seen a convincing argument - although it would be a no-brainer decision if there were no or only a very small cost difference.

Plenty for me to think on clearly.


Point taken on the microbore for those saying that. My plan / hope is to install the new system (as the boiler really is >10 years old so presumably really inefficient) then once all the pipes and rads have been flushed and we have a decent pump, see how it performs. If it's still slow then we attack the microbore (which is only on the downstairs rads) - that means a lot of mess and plastering so I'm not going to touch it if I don't have to... but if it needs doing I definitely will.

 

[SimonG]

Stay vented, no problem. That will save you the annual service on the unvented cylinder as well.

 

[Ray Stafford]

Fair question - but as above really, do the benefits warrant the additional costs (moving cylinder, altering pipework, replacing shower controllers)?

I haven't quite seen a convincing argument - although it would be a no-brainer decision if there were no or only a very small cost difference.

Plenty for me to think on clearly.


Point taken on the microbore for those saying that. My plan / hope is to install the new system (as the boiler really is >10 years old so presumably really inefficient) then once all the pipes and rads have been flushed and we have a decent pump, see how it performs. If it's still slow then we attack the microbore (which is only on the downstairs rads) - that means a lot of mess and plastering so I'm not going to touch it if I don't have to... but if it needs doing I definitely will.

There isn't a right answer, because we don't know how much you value the benefits of the unvented system, or how readily you can afford it.

Certainly, if I was installing your system as new, on a blank canvas, I would use unvented. I would also try to avoid the micro-bore. There is nothing intrinsically wrong with micro-bore, but it is less forgiving of dirty systems than the larger bores. Lots of people in the industry also associate it with cost-cutting, and installers who are driven by cutting costs to the bone often make other compromises elsewhere (poor labour, cheap materials) so we tend to suck our teeth when we see it. Its a flag highlighting potential problems, not necessarily a problem in itself, all the time.

Finally, installers like to cover their asses. Vented hot water systems often have pressure related performance issues. Householders sometimes have higher than reasonable expectations "I didn't pay £2000 to have a crap shower" not understanding the the laws of physics aren't interested in the size of their bill. So to be sure of delivering a system that the customer will be happy with, the easiest (and correct) recommendation is to go unvented.

 

[VentOrUnvent]

Thanks Ray, really helpful reply.

The money's there to spend on unvented if we'll get extra value for that spend - and as you say it's about valuing the benefits.

Good suggestion on performance under load - we have a full house this weekend so will run the 3 showers simultaneously to check, thank you (for reference running 2 at once at the moment still gives great showers).

Thanks again for the reply. Genuinely trying to learn more about vented and unvented here - still undecided between the two still although leaning towards unvented just because it's what everyone is saying even if it's quite hard to put a £ figure on the benefits ...

 

[Ermintrude]

I would change to unvented. I wouldn't rip out microbore
I would pay some one to design system properly and provide you with a specification and then install it.

Microbore provides a slow heat flow - small pipes small heat delivery. If u fit a massive boiler your boiler will cycle and not last long.

Add up the Energy used to heat your home (use an online calculator)

Then add for DHW

I would say 300l cylinder.
Fit one that's solar compatible as later in life u can add solar thermal.
Use a Decent quality cylinder. Mutts mutts being an ACV then joule or OSO. A center store is a megaflow in different clothes and 50% cheaper.

Zone is good idea.
Either Evo home - you could do this at a later date - just need to have a connector left outside boiler case for power and switching.

Get weather compensation.

 

[LaMont5way]

Have you considered just making the heating circuit unvented and installing a system boiler, you could also fit a more efficient new cylinder. This would improve gas consumption plus allow you to keep your current power showers. Would save a lot of money and make the microbore undoubtedly perform better after a good flushing.

 

[paulusgg]

I fit quite a few unvented cylinders as I work for a loft conversion company which very often requires the removal of the CWSC and customers are almost always impressed by the improved performance. However, most gravity systems use a 15mm rising main to fill the CWSC the chances are you would need to upgrade the main to the new unvented cylinder to 22mm. It's also necessary to use the balanced take-off from the unvented cylinder control set for the cold, especially if you have mixer taps. Usually this is fairly simple as the rising main goes past the cylinder on its way to the loft and all the cold services return past the cylinder so its just a matter of reconnecting correctly!

In respect of the size most manufacters would recommend for a 5 bed 3 bath house 250/300L units

And personally I'd go with a system boiler