New boiler - Viessman or Vailliant

[u587162]

Which of the above two boilers would you recommend we have installed?

Also it was suggested that we have 2x 26KW systems rather than one large 40 KW system. This would help power the UFH to ground and possibly first floor, radiators to second floor of a house size of approximately 4000 ft.²

It was also suggested we have 2x 250litre mega flows.

 

[muggles]

Intergas

But of the two you've mentioned, you haven't said which models so it's hard to say. The Viessmann 200-series is very good by all accounts, the 100-series not so much. Similarly, are you looking at Vaillant 4-series or 6-series? Entirely different beasts.

Two boilers are better than one on a large property, set up in a cascade on a low-loss header with proper cascade controls. 500 litres is a LOT of stored hot water, especially as they'll reheat very quickly if you've got the right controls on them; how many people are you expecting to need hot water at any one time? Incidentally, I don't rate genuine Megaflo cylinders, you're much better off with an OSO Super Coil

 

[Dan Robinson]

Depends on the version of the boiler.... the 200 series Viessmann are incredibly clever if you are willing to spend on the controls. They have a better heat exchanger too IMHO over the Vaillant.

However, I think the Intergas or Atag are better boilers.

Tricky to say without seeing the house, but at 4000 feet, it is a little tricky to justify the cost of two boilers. As Muggles has said - two cylinders is a lot. I would look at higher performing cylinders such as the ACV.

We're finishing off a place at 6000 feet with pool and silly hot water requirements and that has a single boiler and cylinder.

Just had a look at the drawings - 4 bathrooms, 5 showers and a steam room.

 

[u587162]

Intergas

But of the two you've mentioned, you haven't said which models so it's hard to say. The Viessmann 200-series is very good by all accounts, the 100-series not so much. Similarly, are you looking at Vaillant 4-series or 6-series? Entirely different beasts.

Two boilers are better than one on a large property, set up in a cascade on a low-loss header with proper cascade controls. 500 litres is a LOT of stored hot water, especially as they'll reheat very quickly if you've got the right controls on them; how many people are you expecting to need hot water at any one time? Incidentally, I don't rate genuine Megaflo cylinders, you're much better off with an OSO Super Coil

I remember the plumber saying Viessman 100 range but I'm not sure of the Vailliant.

Could you please explain what you mean by cascade and low loss header?

The other issue is that we are a very small family (1 baby) but bought into a large project. What can we do to ensure the house is scaled up correctly to potential capacity without the associated running costs? Can we just switch off one boiler and mega flow?

 

[u587162]

Also if I'm offered the option, hoe much more are we talking to upgrade from the 100 range to the 200 range and it true they offer a 10 year part and labour warranty for a small nominal fee?

 

[Dan Robinson]

Installing two megaflows for a family of three is insane.

the 100 series Viessmann is, well, budget.

If the scheme was to facilitate for future expansion, we would either look to install a single cylinder to deal with your current needs (say 210 litres) with the tappings to add a second as/when/if it was needed.

IF you go for two boilers, they would control themselves.

Low Loss Header = a smallish canister that is heated by the boilers, then house and hot water then draws what it needs from this.

This is a single boiler with low loss header that we fitted to house similar in size to you.

Left pump does the hot water.
Middle does the underfloor heating
Right does the rads.

The boiler knows the difference between heating and hot water and changes the way it operates accordingly to maximise efficiency.

This is an Atag boiler BTW.

Cascade = a control regime where, if there are more than one - the boilers work in tandem to deliver the heat required in the most efficient way possible. Some alternate the lead boiler to even the wear and tear.

 

[Dan Robinson]

This is a cascade of 4 boilers - the little panel on the right alternates which of the 4 boilers is the lead every 24 hours. It then sequences which boilers are used to maintain the required temperature in the system.

Had some real fun with this lot last week - all the office workers are warm and toasty now though .

 

[u587162]

Installing two megaflows for a family of three is insane.

the 100 series Viessmann is, well, budget.

If the scheme was to facilitate for future expansion, we would either look to install a single cylinder to deal with your current needs (say 210 litres) with the tappings to add a second as/when/if it was needed.

IF you go for two boilers, they would control themselves.

Low Loss Header = a smallish canister that is heated by the boilers, then house and hot water then draws what it needs from this.

This is a single boiler with low loss header that we fitted to house similar in size to you.

Left pump does the hot water.
Middle does the underfloor heating
Right does the rads.

The boiler knows the difference between heating and hot water and changes the way it operates accordingly to maximise efficiency.

This is an Atag boiler BTW.
View attachment 87559

Cascade = a control regime where, if there are more than one - the boilers work in tandem to deliver the heat required in the most efficient way possible. Some alternate the lead boiler to even the wear and tear.

1. Could a low loss header be regarding as a smaller interim storage of say a few litres of hot water and operate a bit like a condensing combi which has maybe 5 litres of hot water stored inside the boiler?

2. Is there a huge running cost saving between say a 70 litre tank and a 210 litre one?

3. How easy is it to provision the services for an additional storage tank should it become necessary to add one later?

4. If we did go for a small storage tank of say 70 litres, what are the potential drawbacks - not enough hot supply or pressure drop if 2 or more showers are on at the same time? Would the boiler(s) not be powerful enough to generate enough hot water to start replenishing the storage tank as it's being used? Can a small tank have any negative impact on UFH or radiators?

Thanks.

 

[Dan Robinson]

1 That's not what it is for.

2 70 litres is too small.

3 Easy

4 You are looking at things arse about face. Fit a fair size single cylinder now with provision for a second later. I would suggest 210 litres, but we don't have the information to say categorically.


Really these are questions, that in a job this size, should be the concern of the installer.

 

[HERTS P&D]

U58761, why don't you just get Dan round.

Andy

 

[dilalio]

all the office workers are warm and toasty now though .

I'll bet they're still arguing over the stat setting(s) tho! She's cold, he's hot, etc etc

 

[Dan Robinson]

 

[Dean744PiN5]

on a job this size don't look to compromise quality for the sake of saving a few pounds in the grand scheme of things. A project like this deserves respect and a proper heating engineer to design and install it.

 

[u587162]

Hi

I agree with all the comments here. My issue is that my building contractor is handling the whole house build project, so he uses contractors that he always uses and we have agreed a cost for the house so I'm not paying extra or saving less for this or that. But what i dont want, as others have correctly said, is to put in a large system which I know will far exceed what we need and unnecessarily increase our running costs (so I think a 210 litre tank is a good idea). I know your cant buy into a large house project and then ***ch about the running costs but by the same token I'm looking for alternative opinions here to strike that compromise rather than accepting what the plumbing sub-contracting firm is proposing (based on the house size). He has only seen the house for the first time yesterday and I met him by chance for 10 min to have a quick chat with him whilst the building contractor was on site, so I was going to ask him for some suggestions based on my research here.

If another storage tank is fitted (since I'm not paying extra), can it be switched off as such, much like a secondary return value pumping hot water to far areas of the house which will not be occupied for the foreseeable future?

 

[Dan Robinson]

Fit it and leave it drained and isolated then.

Otherwise you will have legionella issues.

Or will be heating twice the water you need.