Unlimited hot water with 4 bathrooms - is it possible?

[Indy]

Ok so title is a bit vague but the summary of our new build is that we're going to have:

 

1. Gas Boiler - for various reasons, I don't want an ASHP (gas fire, gas hob and generally not liking the over inflated quotes we've had for ASHPs).

2. UFH on both floors - which probably means 2 manifolds

3. 3 full bathrooms + 1 guest cloak room.

 

The general recommendation is to go for a system boiler plus something like a Megaflo cylinder so we have pressure when more than one person is in the shower.

 

In our current house, we have a combi boiler which basically means that we have unlimited hot water when we turn the shower/taps on. Works quite well but does mean that no more than 1 person can really use the bathroom at one time - which happens very frequently. We have 2 young kids who love nothing more than standing under the shower for 15-20m or even more pretty much daily and this may prove to be quite limiting when it comes to having a cylinder of say 300l which is going to get emptied in 2 showers, and then we'd have to wait for the water to heat up again.

 

Patience is not my strong point so I'm looking for suggestions on what others have implemented that allow them to overcome this problem. From what I can see:

1. Go for a much larger cylinder - 400l or even 500l (prices do jump up quite significantly).

2. A separate combi boiler for the kids bathroom and the standard setup for everything else - seems like overkill and I'd like to keep it to one boiler if possible.

 

Any suggestions?

 

 

[JohnMo]

Simple way

With UFH you need low flow temperature, so weather compensation is ideal. To get weather compensation you need to priority domestic hot water (so X or W plan). Definitely do not go the normal S or Y plan.

 

To keep boiler happy and not short cycle you need to run zone fully open system. So switch your head off to multiple thermostats one will do.

 

Cylinder choose a heat pump cylinder - yes a heat pump cylinder. It will have a 3m² coil so hot water recovery is quick.

 

Boiler choose, Viessmann, Atag, Intergas. If you plumber looks blank at you when you ask for priority domestic hot water, get a different one, they won't do you any favours.

@marshian will be able to tell you facts about figures on the reduction in gas consumption going this route.

 

A other way to do hot water with a combi boiler is to have a pre heat cylinder. It moves away from the single shower situation and does DHW. Alfa boilers sell a stand alone cylinder, but Vaillant, Viessmann and others do storage combi boilers. This will give you never ending hot water and with an external sensor weather compensation - a simple solution.

 

The important bit is look at min turn down rate, you don't want a boiler kicking out 12kW for a house that needs 4 or 5kW or less.

 

2 boilers - no

[-rick-]

What @JohnMo said but also if you have a household with many people having long showers, may be well worth your time looking at whether a Waste Water Heat Recovery System might be worth it. They claim they can save up to about 50% of the energy used to heat shower water. Pricey but with your water usage might pay for itself quite quickly and much easier to install if planned in advance.

 

The solution I liked the best when I spent some time looking at this is: https://recoup.co.uk/products/pipe-hex-range/pipe-hex/

 

Don't have personal experience though.

Edited 15 hours ago by -rick-

[SimonD]

You won't get unlimited hot water as such but you can have a decent DHW strategy that will satisfy you as a family.

 

Similar to what @JohnMo suggests, make sure you have a priority hot water installation. As I know Viessmann's and I assume your new build is pretty well insulated and not too massive, I reckon you could get away with an 11kW 100-W system boiler. Modulates from 11kW down to just over 1kW on central heating but will give you 19kW output on a 4 pipe priority hot water setup. The system with then start heating your hot water to your cylinder while showers/baths are being used so will give you much longer run times from your cylinder. This way you don't have to massively oversize your cylinder either.

 

Personally and professionally, I'd suggest staying well clear of any combi setup for a large family house with multiple bathrooms and high hot water demand.

 

 

[Temp]

Perhaps check that the cold supply to the house can deliver enough for 2+ showers at decent pressure.

 

Then what @SimonD said. Think you will need a decent sized tank. 

[marshian]

5 hours ago, Indy said:

In our current house, we have a combi boiler which basically means that we have unlimited hot water when we turn the shower/taps on. Works quite well but does mean that no more than 1 person can really use the bathroom at one time - which happens very frequently. We have 2 young kids who love nothing more than standing under the shower for 15-20m or even more pretty much daily and this may prove to be quite limiting when it comes to having a cylinder of say 300l which is going to get emptied in 2 showers, and then we'd have to wait for the water to heat up again.

 

I guess because the kids aren’t paying the bills they aren’t bothered about wasting energy and water

 

I’d be going one boiler and two tanks - a smaller one for the kids bathroom - when the shower goes cold they’ll soon learn to be less wasteful with energy and water 🙂 

 

On a more serious note one boiler - with a good turndown rate for the CH demands of the house but a decent output for water reheat times to be quick 

 

urban plumbers did a set up a while ago with a fairly small tank that could be re-charged almost as it was used - worked like a giant storage combi but not a combi was how he described it at the end.