Flow- Vent- Feed -Pump

[fixitflav]

Message from Viessmann technical support about height and static head for feed.

I had a look at various Viessmann manuals and couldn't see that pic anywhere. Not important, but I'd be interested if you can identify.

It differs from the one you posted in #31, as the 1m (~ 40") is to the tank water level, not the top of the vent loop. Assuming your 7ft (= 84") includes the 18" for the vent, on the later one you won't get it in.
If it's any help, the manual for my 20+ years old Ideal boiler shows 18" minimum from top of boiler to tank water level. Or it might be to the flow pipe level, but obviously you will keep that as close as poss to the top of the boiler if you're tight for headroom.

 

[desktop987456]

Viessmann manuals

Ah, the pic in post 31 was from manual but I put the numbers various deimensions in it! Sorry if my editing has misled you.

Viessmann technical support sent an email, this pic is not in any of the manual that I have seen for this model i.e. dimensions with water level.

It wil be pretty tight in terms of available space I have in balcony, I have seen a few installers also mentioning 18" in their videos as you have mentioned in your manul. Worst off, I may need to go over the roof.

 

[Madrab]

Only real spec we ever worked to was the 450mm curved vent over the water level to avoid initial pumping over due to pump surge/expansion.

Can you give us the GC number off the boiler data plate - should be 41-819-xxx, that will allow an exact spec to be looked at. Some of them actually ask for 0.2bar as a min head (2m), that will be for filling/air purging purposes no doubt. So as long as there is enough head to purge the system then fine.

 

[desktop987456]

Can you give us the GC number off the boiler data plate - should be 41-819-xxx, that will allow an exact spec to be looked at. Some of them actually ask for 0.2bar as a min head (2m), that will be for filling/air purging purposes no doubt. So as long as there is enough head to purge the system then fine.

Sure.

 

[Madrab]

OK ... Page 20 of that boilers manual - Open vented heating system: The static head must be at least 0.2 bar.

101-w Compact

So ultimately that boiler's looking for 2m head, so ideally the cistern should be 2m above the system so the open vent would be another 450mm above that again. That is will be to ensure that the system can be purged of air easily so if you don't have that height then as high as you can get it will have to do. The min height of the vent, again, will be to avoid any water being pushed up and out of the vent when the pump kicks it etc.

You only need to worry about that if you start getting issue with pumping over or problems bleeding the system

 

[fixitflav]

Open vented heating system: The static head must be at least 0.2 bar.

Be useful if they'd specify at what point on the boiler the pressure is measured. 0.6m boiler height is a fair chunk of the total 2m.

 

[desktop987456]

OK ... Page 20 of that boilers manual - Open vented heating system: The static head must be at least 0.2 bar.

101-w Compact

So ultimately that boiler's looking for 2m head, so ideally the cistern should be 2m above the system so the open vent would be another 450mm above that again. That is will be to ensure that the system can be purged of air easily so if you don't have that height then as high as you can get it will have to do. The min height of the vent, again, will be to avoid any water being pushed up and out of the vent when the pump kicks it etc.

You only need to worry about that if you start getting issue with pumping over or problems bleeding the system

Thanks. Its 2m + 0.45m so can't install the boiler in Balcony with 2.1 m available height? If I have to install it at that location which is my only option since it is covered, excellent gas pressure, condensate drain and is closer to bedrooms and lounge then I have to take the cistern over the roof. Instead of drilling through the roof (8" concrete slab) can the vent and feed pipes have elbows (5) so I can take it along the ceiling of balcony and then up over the roof without compromising the required head at the boiler? Not sure, the only sure answer would be to measure the head via a guage at bottom of the feed pipe after installing the pipe.

what point on the boiler the pressure is measured. 0.6m boiler height

Flow and return pipes are at the top of the boiler (not at the bottom) and the pipe goes into HEX at the top.

 

[Madrab]

Thanks. Its 2m + 0.45m so can't install the boiler in Balcony with 2.1 m available height?

No you can, you just need to be aware that a reduced head of water may make the system slower to vent/purge the air from it. An atypical setup would have the cistern in the attic and the boiler on the ground floor therefore 0.2m head wouldn't be hard to achieve and they'll quote that to ensure the installation conditions are met from a support perspective. The diagram they have sent with the 1m head min will be ensure that the pump surge and positive pressure will not circulate up and over the vent, therefore presume that any extra height will be to aid in filling/purging.

Be useful if they'd specify at what point on the boiler the pressure is measured. 0.6m boiler height is a fair chunk of the total 2m.

Looking at their diagram it looks like it's from the top of the water in the cistern to the entry point of the boiler. With an OV it is usually measured from the cistern to the highest point in the system.

 

[Johntheo5]

Came across this from a gas boiler MIs, can't remember which one.

 

[fixitflav]

Looking at their diagram it looks like it's from the top of the water in the cistern to the entry point of the boiler.

AFAIK we haven't got a Viessmann diagram, just the 0.2 bar figure. I agree it probably means 2m from the top of the boiler to the tank water level, but it would be better if it was made clear.

 

[fixitflav]

Came across this from a gas boiler MIs, can't remember which one.

View attachment 313157

I would take that with a generous pinch of salt. In Fig 3 dimension C, 150mm looks very sparse, and much lower than other makers say. Dimension A is useless as the angle of inclination is not given. Everybody else says the vent loop height, 450mm (vertical), is constant, not varying with boiler output. And it certainly wouldn't want to be as low as 50mm, giving vertical height around 30mm, for any boiler size.

 

[fixitflav]

Sure.

I'm sure you have considered putting the new boiler where the old one is, but doing that would solve most of your problems at a stroke.

 

[desktop987456]

No you can, you just need to be aware that a reduced head of water may make the system slower to vent/purge the air from it. An atypical setup would have the

That's great then.

I'm sure you have considered putting the new boiler where the old one is, but doing that would solve most of your problems at a stroke.

I have, and its not a great spot for room sealed boiler. I still can have it install there with a weatherproof box around the boiler at a cost of slight inefficiency. The other reason was that I wanted to keep the old boiler installed at that location as backup.

 

[fixitflav]

That's great then.

As long as, in the event of a problem, Viessmann don't say you haven't met their spec so warranty is void.

It still looks tight to me. If you make it 1m from top of boiler to water level, the bottom of the boiler is 50mm off the deck, clearly not on. Using 450mm, like my Ideal spec, it's 600mm off the deck. I suppose that's doable, but it would be awkward to install, and it's a long way short of Viessmann's 2m figure.

 

[Madrab]

Given Viessmann have sent you information stating that 1m head is within spec, if you run to those dimension then it's within their design so shouldn't be an issue. That being said, you are using a boiler in the US that isn't specc'd for the US, (see the top of the data plate for the countries it's designed for), therefore unfortunately I don't think the warranty would even be in play.