Boiler system suggestions to run 2 showers

abankerbutnotafatcat

Alex1983 wrote: »

With unvented you will have a boiler, 1 cyclinder and no tanks in the loft.

You can have the system zoned, each part of the house could be controlled independently and without the need for everything being on and all controlled by a multi zoned controller like hive, don't think the nest does multi zone but I may wrong with that.

Thank you. I think you're right, we were thinking we'd have to have two Nests but I suppose it may also be upgraded to support this.

abankerbutnotafatcat

fezster wrote: »

An unvented cylinder (I have megaflo, but it is overpriced and cheaper alternatives available) is mains driven and so does away with the cold water storage tank in the loft. It replaces your hot water cylinder, but can be sited pretty much anywhere with access to drains and plumbing to the boiler.

You can measure your incoming flow rate using a bucket to time how many litres per minute you have. Use an outside tap closest to your incoming water main. A G3 certified plumber is required to fit an unvented cylinder and they will measure your flow rate and pressure. Typically, you need 2.5 bar and 20 l/min as a minimum. If you have big rain type showers which consume 15 l/min, you'll need at least 30 l/min to run two of them simultaneously. If your water main is already blue mdpe pipe of at least 25mm, you may not be able to upgrade it further. However, even I'm this circumstance you can use an accumulator to boost your incoming water supply.

Best to discuss this all with a competent heating engineer as the time and cost you'll save by doing it right once will be more than offset by his/her additional fee compared to someone who doesn't know the ins and outs.

Thank you for all this. Yes, we'll discuss it at the time with a competent heating engineer, I just like to be as pre-informed as possible before making decisions.

abankerbutnotafatcat

Thank you all once again, this is really helping me understand our options.

I am concerned that if we get a big hot water tank sufficient to feed two showers simultaneously and say six or eight showers in a session then the majority of the time, when it's just us two taking a shower one after the other, we'll be heating far more water than we need and therefore wasting fuel. That's why I like the idea of a combi. Any thoughts?

Alex1983

I'd be surprised if a good experienced plumber would fit a combi knowing the hot water demand your asking for, it would be a poorly designed system.

abankerbutnotafatcat

Alex1983 wrote: »

I'd be surprised if a good experienced plumber would fit a combi knowing the hot water demand your asking for, it would be a poorly designed system.

Oh I know full well that one combi would not be the answer. That's why I was asking whether two might be a possibility.

fezster

abankerbutnotafatcat wrote: »

Thank you all once again, this is really helping me understand our options.

I am concerned that if we get a big hot water tank sufficient to feed two showers simultaneously and say six or eight showers in a session then the majority of the time, when it's just us two taking a shower one after the other, we'll be heating far more water than we need and therefore wasting fuel. That's why I like the idea of a combi. Any thoughts?

You won't be wasting it if you're using it

Unvented cylinders are extremely efficient when it comes to heat loss. I cant remember the figures, but it's 2-3Kw per 24 hours loss, which means in reality, your water will still be hot by the time it comes around to reheating the cylinder the next day.

Also, if just heating the cylinder, they have a recovery time of less than 20 minutes, which means you can usually continuously shower whilst the cylinder is being heated.

abankerbutnotafatcat

fezster wrote: »

You won't be wasting it if you're using it

Unvented cylinders are extremely efficient when it comes to heat loss. I cant remember the figures, but it's 2-3Kw per 24 hours loss, which means in reality, your water will still be hot by the time it comes around to reheating the cylinder the next day.

Also, if just heating the cylinder, they have a recovery time of less than 20 minutes, which means you can usually continuously shower whilst the cylinder is being heated.

Thank you again. The fast recovery time makes it sound like we wouldn't need that large a tank unless everyone wanted to shower in the same 20 minute slot which doesn't seem likely?

fezster

I'd get a tank large enough to fulfil your daily needs for hot water. This means you heat it just once a day in the morning, usually before your heating comes on.

Then on the odd occasion where your hot water usage exceeds your tanks capacity, you just put the HW on for an hour and have it continuously heat during that period as needed.

fezster

For the Megaflo Eco Plus you can find heat loss and recovery times on pages 7 and 8:

https://www.heatraesadia.com/literature/installation-manuals/Megaflo-Eco-Plus-250-300-installation-manual.pdf

fezster

Also remember that you're mixing hot and cold water in a shower. So if your shower delivers 20 l/min, approximately half of that will be hot water and the other half delivered cold direct from the mains. You can use this as a basis for calculating your hot water storage requirements.