Confused... invented Vs thermal store

[dormermike]

Hello

Bit confused so Hoping someone can set me straight. I've had a heating specialist over to advise on a converting my open vent Y plan to a unvented pressurised system and new boiler.

They are advising a unvented cylinder which I thought was the same as a "megaflo" / thermal store but they said nobody really installs thermal stores any more, and unvented are the way to go, but that they'd "look into it".

I appreciate folks install and stick to what they know, but I'm unsure of the pros and cons. The boiler being suggested is a Worcester 4000 system too, at 21kw, which seems small to me and the brochure says for small to medium sized homes. I don't live in a mansion but it's definitely not small.

Can anyone guide me on thermal store Vs unvented please? I did Google and one site said unvented cylinders are for electric heating. I'm gas.

Thanks

 

[dormermike]

Also to add 5 bed detached, 18 radiators, 3 bathrooms with 3 showers and one bath.

 

[Madrab]

Older thermal stores were just sludge buckets but as long as the system is properly managed then that can be avoided these days. Thermal stores o have their place and in certain circumstances/setups are used but unvented is the current standard to obtaining mains pressure stored HW from a standard CH setup

Unvented can use any heat source, not just leccy so gas is fine. It all comes down to the dynamic mains pressure and flow whether an unvented is suitable or not.

A system boiler output will ultimately be determined by radiator requirements. Whether a WB is the better boiler to use is subject to the installers preference and what perks they may be after If you ask 5 different installers, you could easily get 5 different recommendations.

 

[ianmcd]

He is correct, thermal stores are old and inefficient, system boiler and unvented cylinder is definately the way to go

 

[muggles]

Thermal stores are really bad news for condensing boiler efficiency because they run too hot. An unvented cylinder is what you need, preferably set up for priority hot water.

Since June 2022 it's been a requirement of Building Regulations to carry out a full & detailed room by room heat loss calculation prior to replacing a boiler. 21kW could be about right for your home but this calculation needs to be done. www.heat-engineer.com is a good one to use.

 

[flameport]

at 21kw, which seems small to me

Unless all of your radiators are vast and your home has no insulation, 21kW is probably oversized.

Was that sized from the heat loss of the building, or just some random guess?

 

[dormermike]

There was no room by room heat loss calculation, he didn't even go into most of the rooms. Is that what is supposed to happen then, and if it didn't, what does that mean? He is on heat geeks or whatever it's called btw, and seemed to know his stuff. All they do is heating. No plumbing or bathrooms etc. I prefer people who specialise.

 

[ianmcd]

There was no room by room heat loss calculation, he didn't even go into most of the rooms. Is that what is supposed to happen then, and if it didn't, what does that mean? He is on heat geeks or whatever it's called btw, and seemed to know his stuff. All they do is heating. No plumbing or bathrooms etc. I prefer people who specialise.

Usually heat geek guys are pretty switched on, just means that they have been on a course, when getting a new system, many think that installing an over sized boiler is a good Idea, it isnt, a properly sized and controlled and set up boiler will be efficient and will happily work away doing what it is designed to do, as already advised by @muggles priority DHW and weather compensation with a decent boiler and properly set up is what you require, up to you if you think Worcester is your best choice

 

[dormermike]

Thanks Ian. I don't think it's up to me though particularly, as all I'm doing is choosing an installer and giving them my functional requirements. How they design the system is up to them. I don't hugely have an interest in what boiler is installed as long as it's a good brand.

I've been clear that I want to be able to use at least 2 showers at a time. When the guy arrives and we were chatting he said well how often do you really use 2 showers? Well, that's not the point. The point is I want it to work. Not sure if I'm being unreasonable, I don't think so.

So is a per room calculation supposed to be done or no?

Also he didn't seem to know what size tank to install, and this has me quite worried tbh, as he didn't ask how many people are in the house. Said he'd have a think about it.

Hmmm. Nice guy but may need to look elsewhere I guess?

I am clearer on the unvented Vs thermal store anyway, I think, sorta.

 

[Madrab]

as long as it's a good brand

That's the point, that's really subjective and some hate WB and some love them. It's really all down to how well the system is installed and then how well your pro and the company supports you

(edited) I want to be able to use at least 2 showers at a time. he said well how often do you really use 2 showers, the point is I want it to work. Not sure if I'm being unreasonable, I don't think so.

Not at all unreasonable and if the professional was worth using then he shouldn't be trying to dissuade you from what you want, it's entirely achievable as long as your mains can support it. I have 3 showers, 2 kids, me and the missus and all 3 showers could be used at the same time. hence I installed a 250L high recovery unvented but I do have a >3bar dynamic mains @ 22L/Min.

So is a per room calculation supposed to be done or no?

There should be an overall heat loss calculation done on the house so it is understood what the boiler and radiators should be rated at. If it's not getting done then they're just being just being lazy and not doing the job properly IMO

 

[muggles]

Thanks Ian. I don't think it's up to me though particularly, as all I'm doing is choosing an installer and giving them my functional requirements. How they design the system is up to them. I don't hugely have an interest in what boiler is installed as long as it's a good brand.

I've been clear that I want to be able to use at least 2 showers at a time. When the guy arrives and we were chatting he said well how often do you really use 2 showers? Well, that's not the point. The point is I want it to work. Not sure if I'm being unreasonable, I don't think so.

So is a per room calculation supposed to be done or no?

Also he didn't seem to know what size tank to install, and this has me quite worried tbh, as he didn't ask how many people are in the house. Said he'd have a think about it.

Hmmm. Nice guy but may need to look elsewhere I guess?

I am clearer on the unvented Vs thermal store anyway, I think, sorta.

It's absolutely up to you. A new heating system is a significant investment and you should specify that you want a modern priority hot water setup with modulating controls to get the best efficiency.

A room by room heat loss calculation must be done (if you're in England or Wales, I don't think the Scots have caught up yet). Guessing on boiler size almost always ends up with one that is too powerful.

 

[dormermike]

Thanks all. Am getting someone else in to advise. After a chat they've already said they "hate" worcester boilers and always fit Vailant. He did ask, at least, how long I expected to be able to use both showers and suggested an accumulator may be needed. The other guy said I didn't need one, and said it would probably be ok. Minefield.

Any how.

Lots of good info in this thread so thanks very much.

 

[Madrab]

suggested an accumulator may be needed.

Ask them what your dynamic mains pressure and flow is (measured at a full flow outlet with at least another 2 or 3 outlets open), that's critical info,. If they can't/won't tell you then they shouldn't be suggesting anything until you know that.

 

[dormermike]

Ask them what your dynamic mains pressure and flow is (measured at a full flow outlet with at least another 2 or 3 outlets open), that's critical info,. If they can't/won't tell you then they shouldn't be suggesting anything until you know that.

Thanks - will do. Interestingly the 1st guy measured the flow and pressure with a little device. However the tap he used was at the furthest end of the plumbing to the stop-tap as its an outdoor one, and didn't repeat the test with other outlets open (neither did he, now i think of it, verify that no other taps or consumers were on at the time - which if they were it renders his test less meaningful).

Food for thought, thanks again.

 

[Madrab]

Easiest way I test pressure is attach a gauge on an outside tap, as they tend to be full flow bib taps, then run the kitchen tap and a bathroom tap, and monitor the gauge. Flow is easier with a weir gauge or just time filling a bucket over 1 min with another outlet running, then measure volume.