Best heating system for low pressure mains?

[Dan Robinson]

With a break tank and pump set you can pump unto an unvented cylinder and have the tank and pumps out of the way (say in the garage). With ov you are a little more restricted in that the cylinder has to be there as well.

With an Accumulator you do away with the lot and just have the cylinder wherever.

It would be to be a big s0d though - guessing around 600 litres.

You also need a high standing pressure to start with, although again, there are now pumps that can do it,

 

[RickyLee53]

i agree Dan however i think of it this way, how many houses out there have a vented cylinder & the customer needs a new boiler & is thinking about a combi only for us to say no i wouldn't recommend that because your water flow rate or pressure isn't good enough, so therefore why should a new system be any different ? if the house hasn't got the req pressure or flow then roof tank & ov cylinder is the only way to go, don't forget the water co's are reducing the mains supply pressures due to their leaking supply pipes, when did the combi manifacturers ever tell you to remove their flow rate discs due to a flow rate issue but they do now.

OP, you can't pump the mains anymore than 12 ltrs/min (there is a new booster pump on sale now that does comply with this), so a booster pump on the main isn't going to solve your problem if you go unvented, but if you go my route then you can fit a 4 bar twin ended pump to feed your bathroom & shower, of course the roof tank & cylinder must be sized correctly, like i said static pressure means nothing if the working pressure goes down to nearly nothing.

Very true about the static pressure. But surely the only difference between my static pressure and working pressure is friction losses in the pipe?

On the other hand, you say I can fit a 4 bar pump, what is the flow rate? I.e. Its no good been 4 bar at 12l per minute. I'm not much better off. (of course, it wouldn't actually be 4 bar in the pipe if that was the case) but I don't know how the pumps are rated.

Thanks for all your help upto now.

 

[RickyLee53]

Well I went for it and installed a 32mm (waaay overkill) MDPE pipe, I connected to the existing lead pipe at the edge of my property as the waterboard were going to take ages.

The flow is much improved. I haven't done an accurate test yet nor have I measured pressure drop. The bath has a 10mm pipe for the last meter or so, but the upstairs sink is 15mm all the way. I get 2 litres of water out in 5 seconds, but if I run the bath tap as well I still get 2 litres in 6 seconds from the sink.

I guestimate flow to be around 30l per minute, maybe a little more. With this in mind I think i'm going to go the unvented cylinder route. With a Valliant 40kw combi for the kitchen/bathroom sink tap's etc.