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How To Determine Which Type Of Boiler To Go For.


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#1 sphannaby

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Posted 21 January 2015 - 11:23 AM

Hi,

Starting our extension and renovation fairly soon so I am now looking at the type of heating system to go for.

The house is roughly 100m² footprint and 450m³ volume.
Insulation levels are expected to be better than building reg standard but not upto PH standard.
Plan for heating and DHW in the house is as follows:
  • UFH throughout with no rads, two towels warmers to be used though.
  • One bath, two showers and four sinks (not decided whether both showers will be DHW or one electric yet but say both DHW for this example). Average usage of one shower and one bath per day
From jsharris spreadsheet I figure that my worst month at minimum OAT heat input would be 1398kWh based on daily heat loss power of 1878W.

Ideally we would like the boiler hidden from view and this could be house in either the garage or loft as both have ample space.
We have both gas and electricity to the house so we are open to a wide range of possiblilities.

Anyone have any thoughts on which type of boilers I should be considering?
As far as manufacturers go I am willing to invest a little more for better quality (brands I have investigated so far are Valliant, Baxi and Ideal).

#2 NeilW

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Posted 21 January 2015 - 03:36 PM

The biggest problem is getting one that can go down low enough. There is a huge dead zone between 'build regs' standard and passivhaus standard that is simply not served by the heating industry.

The problem is that you need to have a boiler with a fair bit of power so that you aren't waiting days for a shower, but you then need it to modulate down very low to handle the highly insulated house. And it can't do that.

So you end up with a boiler that is constantly cycling and on pump overrun, which isn't good for the boiler and isn't good for fuel economy.

If you get to passivhaus standard then you can warm the house in the depths of winter with a small electric fan heater. So then you just go for a small boiler to warm the water up when you're not getting enough divert off your PV into your tank.

But going all electric quickly gets very expensive if your power requirements are much above passive house standard.

You seem to have to have a maximum demand of about 1000W or the next step up is 10000W (bearing in mind that most of the year you'll be well below the maximum power requirement).

The Ideal Vogue 18 system boiler I'm looking at can deliver up to 19kW of power, but can only modulate down to 3.6kW. The 15 can only get down to 3.0kW

#3 jsharris

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Posted 21 January 2015 - 07:59 PM

You can get around the boiler modulation problem by using a buffer tank, then run the heating off the buffer tank. This works by giving the boiler a decent load to avoid short cyling (by heating the buffer tank) and then running the heating from the buffer tank, so it can draw heat for a fair time before triggering the boiler to come on.

The buffer doesn't need to be very big, 70 litres of so will do for most small to medium sized houses. Just plumb it in to the heating circuit and it'll give enough thermal inertia to keep the system running well.

Alternatively, take a look at fitting a thermal store to provide both hot water and central heating. That might well be your best bet, but needs a bit more room.

Edited by jsharris, 21 January 2015 - 07:59 PM.


#4 vijay

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Posted 21 January 2015 - 08:06 PM

What's the difference between the buffer tank and a thermal store, is it just size?

#5 Nickfromwales

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Posted 21 January 2015 - 10:08 PM

A TS can house a dhw coil so it'll do heating and water ;). Buffers only service heating. That way you can have a 'heat only' device like solar thermal or an ASHP rather than a combi like device ( or other instant dhw heater ) as one larger TS will do both.
Regards, Nick.

#6 vijay

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Posted 21 January 2015 - 10:16 PM

Thanks Nick :)

#7 Nickfromwales

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Posted 21 January 2015 - 10:21 PM

Size for a TS would usually be at least 1&1/2 times the size of a buffer ;).

#8 sphannaby

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Posted 21 January 2015 - 11:54 PM

So if I were to go for a thermal store with a system boiler then the TS would take away the need for a cylinder?
If I went for buffer tank what type of boiler would this be suitable with?

I know its a bad question but anyone have any indicative prices on system with a buffer and also TS style system based on my info in OP?

EDIT:

Forgot to mention that we will also be getting solar PV installed so if this can tie in to any particular type of system to suit my heating needs that is also an option (I don't want to add complication to the system if not required but if it creates a better system that will be cheaper to run then it is there as another option).

Edited by sphannaby, 22 January 2015 - 12:22 AM.


#9 Nickfromwales

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Posted 22 January 2015 - 07:41 AM

The TS doubles up as a buffer and an instant dhw heater. It has a coil at the top which cold mains goes into and accumulates heat from the TS body of primary ( heating ) water. It then comes out as dhw, fast and plentiful btw.
You'll then not need a buffer with a TS.
You'll only need a buffer to run ufh off a gas or oil boiler. The problem isn't when you turn the heating on at first as the heat demand is higher then, the problem ( short firing / cycling ) occurs when everything's up to temp and the heat demand is very low. The boiler simply cannot match that low demand flow temp and just starts kicking in and out, lighting - producing heat it cannot shed - and going out again almost instantly - then it starts again in rapid succession aka ' short cycling '. This usually causes the boiler pump to run continuously and can fatigue a boiler far sooner. Manufacturers will state in most installation instructions that this should be avoided / designed out in the installation so may affect warranty too if you get a Johnny Jobsworth as your repair agent.
Tbh the big players agent are great, it's only the cheaper manufacturers agents that split the hairs so buy cheap, buy grief.
Costs are down to size and ancillaries.
Boiler prices are available on 'tinternet,
TS ......
http://www.ebay.co.u...=item27b6f6d52c
Give Trevor a ring as he's good on prices and you can't buy direct from Telford. ;)
Regards, Nick.

Edited by Nickfromwales, 22 January 2015 - 07:42 AM.


#10 sphannaby

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Posted 22 July 2015 - 06:38 PM

Just wanting to resurrect this thread if possible.

I'm about to start my build in the next couple of weeks and I was really keen to go with the TS option.
The problem I have had is actually trying to find an installer who was comfortable with designing and installing a syytem incorporating a TS.

Of the guys I've tendered to the one who appeals most to me has suggested a Viessmann Vitodens 200 (35kW) with weather comp used in conjunction with and ACV Cylinder (Smart Line E Plus 210).
He has impressed in many aspects and I suggested TS to him but he was honest enough to say he had never done a TS install and would feel more comfortable offering the above mentioned.

Wondering if Nick (or anyone else) has any experiences with this type of setup and what your thoughts are?

Thanks,

Simon

#11 tonyshouse

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Posted 22 July 2015 - 10:09 PM

Chosen the right boiler, a good start, where will the TS be? In the house?

#12 Nickfromwales

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Posted 22 July 2015 - 10:28 PM

The boiler you mentioned is a good quality boiler. A bit pricey, but that's your choice.
The cylinder you mentioned isn't a TS, its an unvented cylinder as far as I can tell.
Can you give some more info,as I read your intro and see your not building from scratch. You also havnt mentioned if your having solar PV or not which are all fundamental to choosing the right setup.
Why do you think you need a cylinder at all? You may get away with a big combi ;)
More info please, number of occupants, two showers ever need to be run simultaneously, radiators or Ufh etc etc.
regards, nick.

#13 sphannaby

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Posted 23 July 2015 - 09:41 AM

View PostNickfromwales, on 22 July 2015 - 10:28 PM, said:

The boiler you mentioned is a good quality boiler. A bit pricey, but that's your choice.
The cylinder you mentioned isn't a TS, its an unvented cylinder as far as I can tell.
Can you give some more info,as I read your intro and see your not building from scratch. You also havnt mentioned if your having solar PV or not which are all fundamental to choosing the right setup.
Why do you think you need a cylinder at all? You may get away with a big combi ;)
More info please, number of occupants, two showers ever need to be run simultaneously, radiators or Ufh etc etc.
regards, nick.

Hi Nick,

Details of build are as follows:

The house is roughly 100m² footprint and 450m³ volume and has standard gas grid connection.
Insulation levels are expected to be better than building reg standard but not upto PH standard.
Plan for heating and DHW in the house is as follows:
  • UFH throughout with no rads (UHF will be in screed on a 200mm EPS100 base and finished with Micro-topping surface) .
  • One bath, two showers and four sinks. Average usage of two shower and one bath per day (occupancy is 2 adults two kids).
  • Old garage will act as a plant room so space is plentiful for whatever hardware is needed.
From jsharris spreadsheet I figure that my worst month at minimum OAT heat input would be 1398kWh based on daily heat loss power of 1878W.

We will be having solar PV but to what size I'm not sure (need to take plans to Solar company to see what I can achieve with my roofspace), so we can take advantage of immersion using PV.

I realised the ACV i mentioned in my last post was not a TS but was hoping you could give thoughts on if this ACV cylinder is any good. The plumber who is quoting for this is saying the ACV cylinders are far superior to a standard unvented cylinder due to its tank in tank deisgn giving much quicker recovery rates.
I really did want a TS but it has been so difficult trying to locate someone in the north east of england who is comfortable with working with them!!! A real pain but the build is progressing and I need something in place so I may have to miss out on the TS hence the reason for this query.

I must admit the cost of the Viessmann seemed a lot but if its worth it then I'm willing to pay. On the other hand if I'm paying for features that I don't need then I'd rather put the money to use elsewhere.

I've tried to attach my drawings to this post but can't figure out how to do it right now!!

Nick,

If this was your house and you couldn't fit a TS what kit would you go for?

View Posttonyshouse, on 22 July 2015 - 10:09 PM, said:

Chosen the right boiler, a good start, where will the TS be? In the house?


#14 tonyshouse

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Posted 23 July 2015 - 05:29 PM

Same make with hot cylinder

#15 sphannaby

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Posted 23 July 2015 - 07:11 PM

View Posttonyshouse, on 23 July 2015 - 05:29 PM, said:

Same make with hot cylinder

So you would go Viessmann but not the ACV cylinder? What type of cylinder would you go for Tony?

#16 Nickfromwales

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Posted 23 July 2015 - 10:18 PM

Ok,
I don't understand why plumbers can't get their heads around the installation techniques / principals with a TS. It couldn't be simpler tbh.
Boiler flow goes in, boiler return comes out.
Ufh flow comes out, Ufh return goes in.
Cold water goes in, ( to the DHW coil ), and DHW comes out.
Where is the compilation? It really is that simple.
Far less components than an UVC install, no complex multiblock and pressure relief & reducing valves for the cold / hot water side. I really am lost as to how there's such a grey cloud over this.
The tank in tank is a load of nonsense to me tbh, and the recovery times are nonsense too as they refer to recovery of part of the water volume so of course it'll be quicker. The statement that its far superior shows an inexperienced view IMHO.
A tank in tank design just isn't needed and takes up space where a full premium temp volume could be stored, taking full advantage of your PV too.
The big no no here is the Ufh. You can't run Ufh from an UVC, but you can from a TS. You don't want to run Ufh directly from the boiler btw, in case your plumber is suggesting that :unsure:
Fwiw, I think your plumbers remit it plain wrong for this instance, and as far as the Veinssmann is concerned, the equivalent Vaillant has a better modulation ratio ;).
How much is the particular acv tank that your looking at?
Regards, nick.

#17 sphannaby

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Posted 24 July 2015 - 06:27 AM

The 300 litre ACV tank is being quoted at £1450 +VAT (or £1000 +VAT for 210 litre version) so by no means cheap!

The plumber is suggesting to run the UFH direct off the ACV tank, is this a big no-no? If so then I guess I need to steer well clear.

As an update I may have found someone who for a TS system. They are not particularly local but they are willing to travel. If they can provide a better solution I'm willing to pay the extra labour/travel costs rather than pay for an expensive boiler and cylinder which current plumber may be suggesting.

Nick/Tony, with regards to a TS what are the thoughts on pump for UFH? Is it best for a pump on each UFH manifold or can pump be installed direct at TS on UFH loop connection? Don't know whether it makes any difference but UFH will be over two levels in my property.

#18 Nickfromwales

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Posted 24 July 2015 - 11:36 AM

Having Ufh running off the Acv will further increase recovery times as the smaller, hotter section will suffer IMO. Simply put, you'll be able to draw dhw off quicker than the Acv can replace it.
For comparison, I've just fitted a 500ltr TS with a 46kw 28mm high flow dhw coil for £1225 complete ( including immersions ), delivered. That was a telford unit, S/Steel and extra insulation sprayed on ( in that price so a standard unit with regular insulation and a 22mm coil would be cheaper again ) ;).
If your happy with your original choice plumber I would speak with him again, it really is a more straightforward job than fitting an UVC :wacko:
Re the Ufh, all you need is a 2-port zone valve, one for each floor / manifold, and then 22mm pipework to each ZV and then the pump ( OEM supplied with the manifold btw ) will pull the hot water by itself. Very rare to have to pump the flow from the TS tbh, and I'd only do that if your Ufh was hideously wasteful of heat and required above average heat flow.
The TS I've just mentioned is serving 4 floors of Ufh via 2 manifolds, one on the ground floor next to the plant room, and another on the 2nd floor. Both work fine without additional circulators ( pumps ) and the place is roasting. :). It's also a very poorly installed ufh system ( there already but never worked so they rang the caped crusader ( me )) so is an example of how well this can perform in the most adverse of situations.
I'd recommend a 3/400 ltr TS ( to take full advantage of PV ) and a Vaillant 630 system boiler to feed it.
FYI, a TS with a boiler feeding it direct, eg on demand when needed, will give constant, instant dhw 24/7. ;). It'll have losses, but so will an UVC, and if you've got PV then any cylinder will be heated for a lot of the day anyway.
Regards, Nick.

Edited by Nickfromwales, 24 July 2015 - 11:51 AM.


#19 sphannaby

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Posted 21 October 2015 - 07:41 PM

My thoughts have turned back to my heating system now.

Company who came out to quote for installing TS were no good. Turns out they class a UVS as a TS and when I mentioned some of the principals of a TS you guys have brought to my attention they were not too keen. Said they would fit but any associated risk would be with me as they were not 'authorised' TS installers! Anyway the quote came back at £8.5k so they priced not to get the job.

After a bit gentle persuasion I have convinced my plumber mate to do the TS install based on the info from you guys (especially Nick who said it couldn't be simpler ;)) .

I've decided to go with the Valliant recommendation from Nick and with a Telford TS.
I've been on the Telford website and have an issue as to which type of would be best for my set-up (Open vented combination type, cylinder type or sealed type).
Am I correct in thinking that the open vented or cylinder type would need a feed/header tank and a sealed one would not?
If so then I'm looking towards the sealed type (if it is suitable to go with the Valliant system boiler).

I've attached the image of the sealed system set-up I was thinking about (300 litre) and I have a few questions.
  • The set-up shows heating flow and return as 28mm. As I will be using this only for UFH I guess I will need 22mm pipe. So do I get Telford to change this to a 22mm heating coil or is it better to leave as 28mm coil and just use reducers to get to 22mm?
  • There is a 1/2" drain shown on the setup. Does this have to be a dedicated drain/sump just for the TS or can it be connected into my standard domestic wastes (or does it even need a physical drain connection and is only there for maintenance)?
  • Finally, what is the purpose of the 22mm thumb vent? Is it an auto vent to relieve trapped air?
Hoping some of the pro's can assist with my education.

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#20 Nickfromwales

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Posted 21 October 2015 - 09:15 PM

View Postsphannaby, on 21 October 2015 - 07:41 PM, said:

(especially Nick who said it couldn't be simpler ;)) .
Bollocks, me and my big mouth :D

As your not having rads, then you could certainly downsize to a 22mm coil for the Ufh to tap off. The only drawback would be heating the house from stone cold, where having the 28mm coil and reducing the unions with bushes would offer a higher kW output to the Ufh manifolds. I strongly doubt you'd ever need the 28mm coil tbh, and 22mm will be fine.
Opt for the extra insulation if you can physically get the TS into the house and into it's resting place, if not, the standard insulation and metal jacket will have to do. Ask the plumber to space all the pipe work accordingly so as to be able to fit decent thickness lagging to them. Don't overlook this ;)
The drain point is purely for a DOC ( drain-offcock ) to be fitted so a hosepipe can be connected to drain the TS completely for eg to replace the immersion heater etc. If the TS is to be mounted a fair distance from a door / outside opening then I do sometimes link the drain point to a run of 15mm pipe and connect it to the prv ( discharge ) pipe that has to run to outside so the system can be drained without doing anything more than opening a gate valve. Your plumber can advise if draining it would ever be a problem.
The 22mm union at the top just gets reduced to 1/2" then 15mm pipe and an automatic air vent to release accumulated air in the TS.
All high points in the system will require them.
The Vaillant ( or any sealed 'system' boiler ) will be fine to use with the TS. If your dhw demand is anywhere near 'high' then I'd fit the 630 minimum, or for the extra few £'s go for the 637 for faster reheat times and better sustained dhw output. Not that you'll suffer with the 630, but for the extra £100 or so it's worth the investment IMO. They both modulate down to the same kW so nothing to lose.

http://www.mrcentral...4ymUaAu8E8P8HAQ
Vs
http://www.mrcentral...AQ#.Vif4M9q9KSM

Pm me your plumbers mobile number if you like and I'll ring him for a chat about the TS birds and bee's :) Like falling off a log lol.
Regards, nick.