New boiler and Unvented Cylinder

[outnumbered38]

Our boiler stopped working last week and we're in the process of gathering quotes for replacing it. We're also planning to extend the house in the spring to add another bedroom and shower room, so factoring this in to the equation now.
We currently have one shower with a pump. I'm told that we can't pump two showers without increasing the volume of the cold water tank in the loft, so being advised that an unvented cylinder would be better. The unvented cylinder is adding £2000 to the quote, but if we can't use a pump for two showers then I'm thinking it's the only way to go.
Anyone have any experience of this? Thanks in advance.

[PigletJohn]

First question: How old is your house, and what diameter and material is the incoming water pipe (look at your indoor stopcock). It might be lead, iron, copper, black plastic or blue plastic.

Second question: Fill a bucket at the cold tap in your kitchen, utility room and garden tap (if any), time it, calculate how many litres per minute it delivers.

[SpeckledyBanana]

Will you want to run both showers at once?

[outnumbered38]

Thanks. House is about 20 years old. Pipe is blue plastic roughly 0.75 inch diameter (hard to measure). Kitchen tap gives about 36 litres/minute.
There are 5 of us in the house so suppose we may want to use both showers at once at some stage.
Not sure of volume of current cylinder but wonder if that would need to be bigger to run two pumped showers anyway. Quote is for a 250 litre cylinder.

[PigletJohn]

probably 20mm plastic pipe. 36lpm is very good so you should be well able to run two showers at a time. It will be an advantage to run a separate pipe to the new cylinder, and to check that all service valves are full bore (this will prevent constriction of flow around the house). Beware of flexible tap connectors with built-in service valves. Both the plastic pipe inside the braid, and the holes in the valve, are surprisingly small. You can get round this by using the next size up with a converter.

250litres is a nice big one. Please don't put it in the loft. It will weigh about 300kg when full, and needs access for servicing.

I would have suspected 20mm pipe to be too small, but if you get 36lpm it's good. The next size up is 25mm then 32mm. It may be etched or printed on the side of the pipe.

[outnumbered38]

Thanks, no it would go in the airing cupboard. Would you recommend an unvented cylinder set up?
Do you think we could pump two showers from old gravity fed vented system?

[PigletJohn]

if you have good water flow, then you can't beat an unvented cylinder.

If for some reason you wanted to use a vented cylinder and cold water tank in loft, plus shower pumps, then the cylinder and the tank would both need to be large, and you would have the extra noise of the pump(s) .

Squirt your existing pumped shower into the bucket, see how many lpm it delivers. Depending on the size and age of your cylinder and boiler, it can probably replenish the hot water at the rate of about 3 to 5 litres per minute, (sorry I do not have accurate figures). Unvented cylinders are usually big enough to do a couple of baths or showers, and replenish in about half an hour. Vented cylinders are usually not as big.

[outnumbered38]

new boiler and unvented cylinder finally being fitted on Monday!