Heating system advice, please

[ban]

We are trying to decide on a heating system for a house we are building and wonder if we would have problems with the sealed system (with fully pumped central heating and domestic hot water). The house will have 3 en-suites, 1 bathroom, cloakroom, utility room and kitchen. We are worried that the flow would diminish if many taps were used at the same time.

In our present house we have an open vented system, with fully pumped central heating and domestic hot water and are happy with that.

What size boiler would we need?

 

[IanDB]

Can't help you with the boiler but I have a similar set up in my house i.e unvented system. I have a Heatrae Megaflo tank. This is pressurised with an air gap and once the water starts to flow it re-fills under cold mains pressure so the the hot and cold run at the same pressure. The benefit is that the hot water pressure is the same upstairs as down. The shower is brilliant.

I have run the hot tap into the bath at full bore and not noticed any appreciable pressure drop elsewhere so it gets my vote any day. I used to have an open vented system and the present one is infinitely better.

The only drawback is that you have to re-charge the air gap every six months which takes about 15 mins otherwise you get a drip from the pressure relief valve.

 

[DP]

My spec would be a 300l Megaflow for sanitaion areas, a combination boiler (Vokera, Vaillant or Baxi 105) supplying hot water in the kitchen/ utility and central heating, a mixture of underfloor heating and rads. Condensing boiler very suited to UF heating.

 

[ChrisR]

First ask your water supply company what the water pressure should be where the house is. 3.5 bar or more means no problems. Then how long is your mains connection? You may need a 32mm (plastic mdpe) supply. hen use 22 or 28 copper to the Megaflo. Use a separate pressure vessel AS WELL AS the internal one (only an extra £50 or so) to eliminate the 6 monthly recharge. Set the precharge on the pressure vessel to say 1 bar, even though everyone will say it should be 3. That will even out supply pressure IF there are any problems. Think about it - the precharge on the internal pressure vessel (air gap ) is ZERO!

 

[oilman]

Set the precharge on the pressure vessel to say 1 bar, even though everyone will say it should be 3. That will even out supply pressure IF there are any problems. Think about it - the precharge on the internal pressure vessel (air gap ) is ZERO!

A question (or two); I agree the airspace precharge is zero, but the external expansion vessel has a rubber diaphram/bladder. When it is charged to 1 bar and the water supply is turned on AND the airspace has been depleted AND the pressure vessel charge has gradually leaked away through the diaphram AND the water pressure is high, the diaphram will be stressed like any other and be likely to have the usual problem of perforating/splitting. If the vessel precharge was set higher than 1 bar, it would have longer before it got to the stressed stage. So would it help if the precharge pressure was higher? Or is it less of a problem than with heating system vessels as the vessel will not see so much in the way of temperature cycles?