Megaflow or not ?

Megaflow or not?
Im in the middle of a house refit and the question has arisen of a megaflow. There are to be 3 showers in the house but my plumber has advised against it because he says running 3 showers and opening a tap will result in a low pressure shower. He advises installing separate pumps for each shower and keep the existing hot water tank

I just wanted to check if this was the case or if megaflow can handle 3 showers running at the same time. Our mains water pressure is 4.5 bars

The plumber seems very knowledgeable but im completely confused now

Any help would be appreciated

 

Good pressure, but what's the flow rate of the incoming supply, and the capacity of the megaflow, and will it refresh sufficiently to keep all three showers going. And would all three showers actually be running at the same time - maybe just two overlapping.

 

I’m looking at a 210 l or 300l one ! 95 percent of the time just 2 showers or maybe one only when we have people over will all 3 be used

I think the plumber was concerned about the pressure of the showers if all 3 were used together

I’m not sure what the flow rate is but when he opened the cold water tap the pressure was a lot and he said it was perfect

 

And what about the flow rate of the shower heads. With a 12 litre head, you will be using maybe 9 litres of hot water a minute, so a 7 minute shower will use up 63 litres, and 3 showers will finish a 210 litre tank in no time unless you've got a high recovery rate. Using pumps on all 3 showers will guarantee the flow rate, but deplete the tank quicker, whereas if you switch the shower on, and the flow rates a bit low, you can decide to brush your teeth first etc.

 

I understand your point and it makes sense thanks very much , it seems that megaflow is the way to go

 

Having spoken to my plumber he seems to suggest an accumulator or pump to go with the mageaflow would be a good idea, does any one have any experience with any of these ?

 

You can only force so much water to move through a pipe. The driving force for any mains pressure hot water system is dynamic pressure and flow rate. Your static pressure is good, but your incoming cold main might be undersized to run 3 showers, most will only run 2. Accumulators are a good way of storing mains pressure cold water , and maintain good cold water flow rates during periods of high demand, recharging when the demand is over. Your plumber should be able to give you a figure in litres/min coming from your kitchen tap, but you will need a decent size UV cylinder and accumulator/booster set to run 3 mixer showers simultaneously - perhaps 300 litres each with balanced hot and cold 22mm feeds. These feeds can be branched off in 15mm to each shower.

 

Megaflows are expensive, generally speaking the more stuff I install the more money I make. So there's an incentive for your plumber to sell you a Megaflow, but he's argued against it. It could be because he's not qualified to fit one (ask him if he has an unvented hot water qualification, and to show you his current licence (badge)), or it could be that he honestly believes that you will get no improvement from the extra expense.
Assuming your current open vented HW cylinder has sufficient capacity (he seems to think so) you may wish to buy 1, 2, or 3 shower pumps. I suggest no pump for the one to be used by teenagers, it doesn't matter how large your cylinder is, pumped or gravity fed a teenager will only come out of the shower after they have used ALL of the hot water. If you can raise the cold water storage tank (in the loft), then great gains can be made in shower performance without a pump, especially in top floor showers.

MM

 

We would need to a buy a new larger hot water cylinder if we wernt going down the megaflo route, and to be honest if i could get rid of the HWC and move the megaflo to the garage it would double the isze of the upstairs hallway as well

 

If your water main is adequate (or if you use an accumulator) go for an Unvented. But don't go for the overpriced Heatrae Sadia Megaflo. The Joule cylinder is well priced and has been recommended on these forums a few times.

An accumulator is just a large pressure vessel which either uses your existing mains pressure to "charge up", or an external pump to charge it. It then releases it's content as required to maintain pressure and flow rate. Be careful when sizing it, though, as it's capacity is roughly half of the actual cylinder size (the rest is air).

 

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