Do I need to upgrade my hot water system? Adding bathrooms and underfloor heating.

[MakesDoAndMends]

Hi,
I've read a few posts here already, but still not sure, so hope to get some advice. I am in the middle of building work and my builder tells me I need a second boiler and additional hot water tank, but I would love a second opinion as the more I read the more confused I am getting.
I currently have a Vaillant boiler and a Megaflo. I'm not sure how old they are - they were here when I bought the house 3 years ago, and could very likely be over 10 years old.
When all building is finished I will have 3 bathrooms, 2 separate loos, and 2 of the bedrooms will have a small sink in them and one will have a bath. The Megaflo is a CL250 and the boiler is and ecoTEC plus 438. Not that I really know what any of that means, other than the Megaflo holds 250l of hot water, which sounds like plenty to me, so not sure why my builder thinks I need more. Can anyone help?

Also may be relevant that I am putting underfloor heating in the kitchen which will also be run by the same boiler. Any more info needed?

No idea but watching as we are in a very similar position, adding a bathroom plus UFH and have a boiler plus Megaflo at present.

The UFH will be replacing radiators and there won't be any more people washing, just more bathrooms, so I'm not sure why more heating capacity is needed? But await comments... especially PigletJohn's!

Nobody can tell you. I had a very similar conversation with a heating engineer recently - could my existing boiler cope with underfloor heating?

it will depend on the size of your house, number of radiators, capacity of the boiler, whether you're having electric showers or plumbing them in, etc etc.

Oh, I also have a huge thing called a Grundfos Home Booster 3.5 bar. I think it is a pump, but it's huge. Anyway, I understand it is meant to help deliver large amounts of water very fast, but whether that's hot or cold or both I have no idea, and also don't know whether it's helping to fill the Megaflo, or send water directly to showers, or baths etc.

Ah thanks Polkerris that makes sense. Boiler is a massive (near commercial size) Keston so hopefully ok. Really must get it serviced and will ask the engineer about capacity at the same time.

Thanks Polkerris - I can provide all that info - I understand there may be limits to the help I can get here, but surely someone might be able to help, even if I have to get a pro to come and assess?

you already have a Megaflo. How big is it? Your boiler can probably heat up a bathful of hot water in about 20-30 minutes, if you want to run baths more frequently than that, you need a bigger one to store more water that has been heated in advance. It can start heating the second bathful shortly after you start running the first. A bath takes in the region of 100 litres.

The booster is a sort of pressure accumulator. Let's suppose you live at the end of a long country lane with a small waterpipe that only delivers 10 litres per minute. You want to run your bath taps at 20 litres per minute. It has a sort of balloon which it inflates when you are not running the taps, so it can squirt out a limited amount of water when you turn them on. I don't know how long yours takes to turn on. Accumulators don't usually have a pump, but I don't know your device.
uk.grundfos.com/products/find-product/home-booster.html

Your heating engineer will have to calculate the incoming pressure and flow, and the demands from your taps. Your existing system cost a lot of money, so I surmise it was impractical to upgrade your water supply pipe, which is a common solution. if you are running a hotel or similar is it probably necessary to have a water tank to store enough for the morning bathroom rush.

If you are putting in showers, they mostly use up the water slower than a bath tap. If you go for a waterfall drencher it will use up the water supply quickly. I suspect you will be OK unless you try to run two baths in quick succession, or at the same time.

Assuming your UFH is being laid in a concrete floor, you will set the timer to start heating it a few hours before you get up, so the boiler will probably not be trying to heat water at the same time.

Yours is not a typical domestic installation

Thanks Pigletjohn,

I'm pretty sure my Megaflow stores 250l of water - model CL250?

I think the system I have was put in because the people before me wanted to be able to have 2 waterfall showers at the same time. It does seem overkill for a house that currently has one bathroom and a small shower room. I also have a water softener. And it's not down a long lane but semi-central London!

I'm not running a hotel, but at times not far off - I have 4 children aged 18 - 23 and when they're not living here I usually have lodgers or airbnb guests, so it may be that there will be a morning rush, but if I change the existing shower heads to something more eco maybe that will help?

Maximum capacity would be 4 people trying to run a bath at the same time, but I imagine that will be very unlikely. More likely perhaps that 3 will want showers at the same time and one washing/shaving at a sink. So perhaps it's not so much about hot water quantity (which probably the Megaflo has enough) but trying to deliver enough water for 3 to have a decent shower at the same time.

I've put on a separate thread a question about the Nebia spa shower, but maybe it's better here as it may be relevant to the whole system - do you know anything about it?

How can I find out if the water supply pipe was upgraded?

Sorry so many more questions, and thanks for your time.

you'll need to look at the incoming water service pipe at both ends. There is probably a water meter or stopcock in the pavement, or wjere the fromt gate used to be when the house was built, and a stopcock where the pipes comes up through the floor where the kitchen sink used to be when the house was built.

If it is blue plastic, it is fairly modern.

It might also be black plastic, copper, iron or lead.

measure its outside diameter

If lead, ask the water co to come and test your drinking water for lead content.

If you have wooden floors or a cellar, it is not very difficult to run a new pipe under them. There would need to be a trench out to the pavement. The water co may cooperate with cost if the pipe is lead or leaking.

btw the water softener would need new large-capacity hoses and valves (about £80) or even changed for a bigger one. All internal service valves and stopcocks should be changed for full-bore ones, and for larger sizes on any new pipes. Watch this, they are more expensive than little ones and plumbers may forget to install the more expensive one they have charged you for.

good

rubbish