Which boiler to use for hot water only?

[propertydev83]

Hi. I'm looking for some advice on boilers best suited to my requirments.

I'm looking to install a new boiler for hot water supply only. Heating is provided by electrical Underfloor Heating system.

The hot water supply will be needed for:
- one bathroom with a bath, sink, and thermostatic mixer shower also over the bath
- one bathroom with sink only (although possibly considering a second shower)
- kitchen sink

From what I've researched myself, it seems that a good combination boiler output of 38kW or more is recommended to have a good performance from a thermostatic shower, and that the mains pressure needs to be around or over 12 litres per minute. However, this boiler recommendation was probably taking into account a home which also has gas central heating system running off the hot water (and also not taking into account a second shower).

Ideally, I prefer the idea of combination boiler giving the benefit of hot water on demand rather than the alternatives; and the recommendations mentioned previously I think were also referring to avoiding the shower performance or temperature being affected badly when someone opens up a tap in the house, which is something I would want to avoid.

Taking all my requirements into account for hot water supply only (for outlets specified) without gas central heating, assuming the mains pressure is good or an additional pump is used, the preference for hot water on demand, and wishing to avoid the shower(s) being affected badly by other outlets being used, what would be the recommended boiler specs or boiler type to use?

Thanks for any help.

 

[Dan Robinson]

Atmos Intercombi or Intergas. In that order and can be enabled for heating when you realise electric ufh is daft as a primary heat source

 

[Tibbot]

A boiler that only provides HW is called a Water Heater. They are available as instantaneous or stored type.

P.S. Mains pressure has to be good, you can't pump it. Otherwise you'll need an accumulator or cold feed/break tank and a pump.

 

[mickyg]

youve got gas to your home and you have electric heating? I take it you have shares in an energy company? The only way that can make sense !

Anyway, in answer to your question you want a Rinnai water heater, provided you have decent flow/pressure they're the best there is.

 

[propertydev83]

Thanks for the replies.

...and can be enabled for heating when you realise electric ufh is daft as a primary heat source

Do you have any experience with electirc ufh as primary or second heat source?

 

[D_Hailsham]

The hot water supply will be needed for:
- one bathroom with a bath, sink, and thermostatic mixer shower also over the bath
- one bathroom with sink only (although possibly considering a second shower)
- kitchen sink

What about cold water? Unless you have a separate tank in the loft supplying the cold taps, toilets, washing machine etc, all water has to be supplied from the one incoming mains pipe.

It seems that a good combination boiler output of 38kW or more is recommended to have a good performance from a thermostatic shower, and that the mains pressure needs to be around or over 12 litres per minute.

A flow rate of 12 litres/min will not be sufficient to supply more than one outlet at the same time.

However, this boiler recommendation was probably taking into account a home which also has gas central heating system running off the hot water

The 38kW will be for hot water only. Combi boilers can only provide either heating or hot water: they cannot provide both at the same time. The size combi required is determined by the flow rate. A 38kW boiler is suitable for a flow rate of about 15 litre/min.

 

[Dan Robinson]

Experience? yep... builder fitted it for a customer and was nearly linched when it cost them £900 to heat a moderate sized kitchen.

Several more that thought it was a good idea because it was cheap as chips to fit in large tiled spaces and now have to play hopscotch across the remaining working bits to get to the warm bit where an electric bill big enough to beat whales and small towns to death with has been delivered by parcelforce.

Fine for a bit of comfort in a small room/ensuite though so perhaps it ain't all bad

 

[propertydev83]

I suppose it may help if I provide some more detail;

At the moment I'm working with a pretty much blank canvas. The reasoning for ufh was that from my research;
- it will be much cheaper to install diy than gas central heating
- it is supposed to be more efficient way of heating a room, from beneath the floor, but in this country it is still pretty much a niche thing unlike in some others
- it is supposed to be more economical to heat a house than gas central heating, saving on running costs
- you can have heat on demand like with gas central heating, but unlike the awful and expensive to run electric storage heaters

I have no experience with it but this is what I've gathered from my own research. Even if this is correct it still leaves the need for hot water. With regards to that, I again appreciate the advantages of hot water on demand and supposed cheaper running cost provided by a combi boiler as opposed to an electric immersion heater with cold water storage tank. As I also would want a thermostatic shower mixer rather than crap electric power shower. I thought that a combi boiler would be needed for this.

This is what brings me to the conclusion that having ufh with a combi boiler for hot water would make most sense as it would be the cheapest to install and run, and give the benefits of heat and hot water on demand....

 

[Dan Robinson]

Sheesh, I hope you weren't ever a research student...

Your conclusions are totally reversed to reality IMHO.

Sorry...

 

[propertydev83]

Well, I know the installation part is true from my own costings, and as you said in your own post ("cheap as chips"). It is also more efficient and potentially more economical to heat from the floor but not necessarily from an electric element. In a new build if the pipework is laid right away as part of the build then it is definitely more economical to have water-based underfloor heating than radiators. It was the factor of using electrical element for heat in this setup that I was not entriely sure of the running cost versus central heating radiators.

I need to get further opinions, but if your assessment is correct then I may have to re-plan and go for central heating instead and pay the extra cost for installation. If I can still do it myself (with exception of fitting the boiler and gas connection) then it will help keep the cost down a bit.

I have no interest in electric storage heaters and electric immersion for water, at least, from my experience at my parents home, the running cost is ridiculous, the power shower performance isn't the best, I don't like the inconvenience of not having hot water and hot heaters on demand, and often the amount of hot water available is pretty slim and factoring in the time taken to re-heat additional water doesn't help.

 

[45yearsagasman]

View media item 44627
Not sure that they do a room sealed version.

 

[Dan Robinson]

Hydronic ufh is indeed very efficient, and on it's own with a combi weather comp is easily added to boost efficiency further.

With mixed heating weather comp is possible but more costly.

The building fabrid requirements are the same regardless of energy source.

Max out the insulation!,!

Hydro ufh is not that hard, and companies will design for you given proper scale drawings.

We use Nu-Heat a lot.

 

[propertydev83]

Doing a bit of further research, and I am again finding a lot of the same stuff I thought about electric UFH, but if I'm honest this is usually coming from companies who sell the products, whether on their websites or on another supposedly "impartial" website. I've noticed a few bits here and there from other people who have used it and it does paint a slightly different picture to what is claimed.

With regards to the wet systems of UFH like those from Nu Heat, do you have any idea on installation costs in a 1970s build semi of approx 84sqm, for both DIY or contracted installation?

 

[mickyg]

electric ufh will cost at least double gas heated ufh to run, no question.
Just send your floor plan to a few UFH companies like wavin, Giacomini, speedfit, nuheat, whoever really ! They will do the plans for you free of charge, tell you what to buy and even send you instructions if you need them. You can diy the floor loops, then just get someone to plumb in the manifolds and fit your boiler.
So glad you havent done it already, you would have regretted that electric ufh !

 

[propertydev83]

I am right to assume that wet UFH will indeed cost more to install than gas central heating with radiators in the same property?

But, provided that the right techniques are used, the running costs would be lower to heat the same property?

I need to go ahead and get an idea of costs from these companies suggested, but I've got a feeling it may be outside of budget. It may be something we will use in future though on a suitable property. I'm glad I posted here. Even though it wasn't what I came here for, it has made me look a bit harder for more impartial evidence on electric UFH and as such may have potentially avoided a fatal error.