In-depth knowledge of electrical and mechanical engineering services. Vaillant boiler questions welcome.
Hi there, this is a common problem and there a few different means of addressing it.
Firstly, you have to consider how capable your combi boiler is in delivering hot water, because they are inherently limited in this respect.
The throughput capacity of a combi boiler is anything from 8 to 16 litres per minute
You generally need 12 litres minute for a good shower
If you provide the details of your boiler I can identify its capacity
There is little merit in spending too much on boosting your Mains Cold Water if your boiler is limited, so we should work from the boiler's capacity.
We are getting a new boiler so will get whichever boiler is best for this.
In that case, for two showers, a combi boiler is not the best option
You would benefit more from having an Unvented Domestic Hot Water cylinder, indirectly heated by a separate boiler.
I think we are limited with storage space though so would need a similar sized boiler and can't really get a water tank?
I see, space limitation is usually the crux in domestic situations
What are we talking in terms of space required for a cylinder and boiler?
OK, you could stick with the combi boiler option - say a Vaillant EcoTEC 831 which should be good for 13 litres/min
The problem is, if you have low Mains pressure, you're likely still going to need to boost it, so you're likely to need: Boiler, Cylinder and Booster
At least a cubic metre for each, and that's a very tight squeeze
If you want the best performance from either system, you may need to boost the Mains - see this product:
But this costs more than a boiler
If your mains pressure is less than 15 litres/min at 1 Bar, there's no other way to honest
Just to be clear: the fix would be to get a boiler, cylinder and booster. Would the booster fit in the 2 cubic metre space as well?
No, you would likely need a separate self-contained plant room
We have carried this out often enough to know there is no short cut
It really depends on how bad the Mains supply is
Ok, so say we don't have enough space for a plant room (we don't), what then?
If the mains supply is marginally less than the capacity of the boiler, then you could also get the booster...
but the booster supplies way beyond a combi boiler's capacity, so there's a high surplus of performance
I am lost. What do you mean by "If the mains supply is marginally less than the capacity of the boiler, then you could also get the booster..." I think the issue now is that we can't fit the booster in?
If the boiler's capacity is only marginally under-supplied, you could add an expansion vessel to the supply
I see. What are the figures in terms of mains supply?
You will need 15 litres min at 2 Bar to supply the boiler
It sounds like you don't have that, but it would be best to confirm what you do have, then calculate the measures required to increase it
The Homebooster's dimensions are 600 x 600 x 1000
The Vaillant EcoTEC models are all (bar one or two) ~ 400 x 350 x 800
Ok, we will look into the mains supply. I have read on other sites that if you just have a cylinder this won't help. It's down to the mains supply. I guess this is where the booster comes in?
Absolutely - the cylinder is passive, it only lets the pressure and flow through that's available on the inlet
The Grundfos Homebooster is the most compact solution you're going to find, and the best balance of cost too
Ok. Does it matter where the booster goes in the house?
No, not really
It's possible to have it separate from the other plant
If you can get it immediately downstream of the Mains Water Stop Tap then that's the best location schematically