New Central Heating / Hot Water system

[ckl139]

Hi,

Have a 3 bedroom midterrace house with two double rooms and one box room. Two rooms downstairs with one to be converted to a bedroom - this is why the current back boiler will need to go. We current have a 450x900 cylinder.

6 people in the house and approx will be having 9 rads. Hot water in kitchen would be used at the same time as someone taking a shower / bath.

We have ruled out the combi option due to the breakdowns people experience and possible flow issues.

The options we now have been quoted on (we told both that we require a lot of hot water and that our current system keeps running out of hot water and recovery time is also long) :

1. Sealed unvented system

Valliant 624 boiler

Valliant unitstor 210l ( I am thinking of requested the 180 but not sure if its better to go with the larger one?)

No tanks in loft I have been told

Approx cost is £5200 including all new CH pipes plus 22mm gas line to boiler.

2. Open vented system

18KW boiler (baxi or Valliant are options - any recommendations?)

450 x 1200 Range cylinder (160 ltr)

Existing cold water storage will be used but they said they can fit a pressure vessel to provide better flow to the new rads on a long run into the kitchen (which is far from the cylinder). Can you do this with an open vent boiler / system?

Approx. £3800(baxi boiler) OR approx £4000 (valliant) + £550 if new CH are requested else system flush is included.


My Questions:

a. based on my house - 3 bedroom (1 bathroom), 6 ppl etc - is a sealed unvented system excessive and only used in multiple bathroom properties

b. do people still install new open vented systems or is it better just to go for the sealed unvented option?

c. based on my quotes above what should I do, as I am confused about what is best for us. I sometimes lean towards the OV system, but then think its an older type and the unvented is the way to go? But then fear at the same time that the unvented system is more prone to failure. The unvented plumber said it is down to installation, which I agree, but I cant help but feel that there are more parts to go wrong....PRV, PV etc.

As mentioned, we are very confused about what to do, typically you only update a system once and its a big cost so we want to get it right.

Any help and advice is greatly appreciate.

First post so if this does not belong here, or I have done something wrong, please politely tell me.

Thanks

 

[simond]

I'd be interested in the pressure vessel to get the rads working in option 2.

I think they meant changing from open vent to sealed system?

Anyway, there is no 'right' answer, it is down to you choosing the right contractor, one that has the skills, owns a powerflush machine which gets used twice a week, and who can translate your requirements into a spec.

Dont expect this chap to be the cheapest.

 

[ckl139]

Thanks for your response. Both contractors are busy locally and the surrounding areas so as for who does the work either will probs be fine.

Our difficulty is choosing the right option from one of the two I have detailed. So I am after opinions about what people would do if they had an option of the two?

As for the pressure vessel for the rad circuit he said it will stil be a OV boiler an vented cylinder. I have not heard of this before.

More opinions welcome as I would like to get a decision made this week - it is driving me crazy you heard and read so much diff stuff!

 

[highleigh]

I am having all new central heating and all existing pipework has been removed. I want mains pressure hot water so have discounted any gravity fed system; In my mind this simplifies the system but this may be my naivety. I will have 2 bathrooms but even if I didn't I would still prefer mains pressure hot water.

 

[ckl139]

My only reservations about unvented is the saftey and reliability compared to say an open vented

 

[Dan Robinson]

My only reservations about unvented is the saftey and reliability compared to say an open vented

Those are the least of your concerns. Pressure and flow to the unvented (go for the bigger one) is more a factor.

As for the choice of product- zzzzzzzzzzzz

Go for the Vaillant if you must.

 

[ckl139]

Hi Dan

Thanks for your response.

Update - I can get the unvented system (210 ltr) done for around £5000 now. The equivilent OV system is cost £4500 including new pipes also and 160ltr tank. OV cost without new pipes is approx £4050.

Could you tell me more about the safety and reliability please? Open vents are proven old tech, with little components to go wrong, what is the like compared to unvented?

If installed correctly (which it should be) is it 100% safe I've read a few posts and seen a few videos linked from here that suggest the cylinder or PV exploding, this seems crazy and would be mad to install in any house if this was truly the case?

As for safety we are removing a back boiler from another room which is being converted to a bedroom for safety reason, are we introducing another threat being the unvented cylinder into the aircupboard in another bedroom.

The Install is of course qualified and seems to be knowledgeable from what I have seen, I just want to get some other opinions from guys in the know.

Yes the installers will do a further check to ensure correct pressure is available.


As detailed, it will be full vallaint install for the unvented. For the open vent I can go for baxi, valliant or worcester even. But I keep steering away from this as I feel I would be taking a step backwards given it is a complete new install almost (rads, cylinder, boiler and maybe even pipework).


As for my choices what are you suggesting overall, unvented or vented?

Also is 210 litre too much for a 6 person house? EDIT: Sorry just re read your post suggesting larger is better

 

[highleigh]

I am putting in a vented thermal store rather than unvented cylinder; I can't believe pv's would be allowed if they exploded but I have underfloor heating so the low temps required make using a thermal store more efficient (Thats the theory anyway). My second coice would have been a unvented pressurised system.

It is costing about 4K fitted for a 300 ltr model with a solar input and a new gas boiler but that is with me removing all the old pipework and making access very easy.

 

[highleigh]

It is a designed system specific to work with ufh. It would be crazy to just connect any old system together and expect it to work efficiently.

My understanding of it is the store gets upto a high temp, making efficient use of the condensing boiler, the thermal store then doesn't call for heat again until it falls below the temp needed to heat the ufh. Once it does it takes the temp back up to a high temp again. Boiler doesn't cycle and gives it time to make use of the condensing feature. On top of the stratification ensures cooler water goes to ufh and hotter for hw.

Obviously this does mean I wont have hot flow for additional central heating rads from the store. These could however be run directly off the boiler or specced for lower flow temps?

I am not an expert on this but this is my understanding of how it works, and the logic seems good to me. I can see that it is not possible to plug these systems together and hope they work.

Don't really want to take over this thread and think it best we keep it on topic. I was just giving my choice which is different to either of the options from the op.

Thanks for your comments through, any information helps me understand how heating systems work.

 

[ckl139]

Thanks highleigh as you say, the underfloor heating is different discussion.

I am still after opinions on my position and two options I have laid out.

There is £500 difference in the two systems (with new CH pipes for both). Opinions appreciated...but please refer to my previous posts for more detail.

I would like to make a decision by tomo evening if possible

 

[Dan Robinson]

Without hard and fast figures with regards pressure and flow rates you are asking a lot of us. However, if the figures stack up the unvented otption is the way to go.

 

[dcawkwell]

All the quotes you have had are very bad recommendations.
I would be suggesting a glow worm ultrapower.

This is a cross between a combi and a hot water tank.

It will supply hot water form the hot water tank but should
the tank run out of hot water it falls back the combi delivery rates of
approx 12 litres a minute. There is also the backup of an electrical immersion heater should the boiler fail. It also provides main pressure hot water and
removes all the header tanks you might have.
Boiler retails for about £1500 quid so could easily put it in for a grand-ish.
Would fit where the existing hot water tank is most likely.

 

[ckl139]

Without hard and fast figures with regards pressure and flow rates you are asking a lot of us. However, if the figures stack up the unvented otption is the way to go.

I will get the engineer to check this again, if he says all good, then we will go with this option.


As for some of the later replies (ignoring the US spam company - why is there soo much on here?!), talking about bad reviews - I am quite suprised to hear this for valliant stuff and its the first I have heard.

 

[ckl139]

Hi folks

I still need some help.

I had another chat with the unvented install and for some reasons I am questioning whether to go for it or not which I wont go into right now.

But it means I am consider the Open Vented solution again. Now would it be a mistake doing this?

Is it ok to go with the pressure vessel on the Rad Circuit?

Shall I change all the CH pipes (£550) to do so?

Shall I go for the Baxi or Vallaint boiler (vallaint will cost around 200 extra)

With 9 rads and a 160ltr tank I was specced a 18kw boiler, do you think I can go for a 200 litre tank on the 18kw?

Your views are much appreciated.

 

[dcawkwell]

Hi folks

I still need some help.

I had another chat with the unvented install and for some reasons I am questioning whether to go for it or not which I wont go into right now.

But it means I am consider the Open Vented solution again. Now would it be a mistake doing this?

Is it ok to go with the pressure vessel on the Rad Circuit?

Shall I change all the CH pipes (£550) to do so?

Shall I go for the Baxi or Vallaint boiler (vallaint will cost around 200 extra)

With 9 rads and a 160ltr tank I was specced a 18kw boiler, do you think I can go for a 200 litre tank on the 18kw?

Your views are much appreciated.

Glowworm ultrapower. All in the one box. Job done.