Back boiler conversion

[MeMyselfAndI]

Hi all
Just wondering if you have any opinions on Sadia Megalife vented cylinders and their ilk ..got to replace back boiler this year and cant fit condenser due to restrictions Ect, is the initial cost for the unit worth the savings? 3 bed semi , Gas fired inst
I know there is no definitive answer but are they worth £500 ???
Thanks in advance

 

[ArtfulBodger]

What "savings" exactly?

 

[MeMyselfAndI]

This is A high recovery tank
example 120ltr unit with a primary coil load of 11.5 KW has a quoted recov time of only 23 mins (70% of capacity from 15deg to 60degs)
just thinking of installing one instead a conventional cylinder and wondered if anyone had any views/exp

 

[PTH]

It's just aa bit of physics:
The maths for the quoted recovery time ddoes work ie.

120 x 70% = 84l

84 x 4.2 x 45 = 15876

15876/(60 x 23) = 11.5 kW

BUT

incoming water temperature is unlikely to be as high as 15 deg, except during heat waves, much more likely to be around 10 deg. And, why 70%? what happens to the other 30% ?

In reality the recovery time to 60 deg is more like 40 minutes.

But this is the same for any type of cylinder or heat exchanger - energy in = energy out +losses. The important thing is how much you pay for the energy, and how much energy you lose or waste. Losses depend on how well insulated the cylinder is and how long it stands idle but full of hot water. By wastage, I mean if you have long pipe runs from your cylinder to the draw offs you will be displacing that amout of cold water before you start getting hot and will be leaving the same amount of hot in the pipe when you have finished.

The advantage that you get is near mains pressure hot water, if that is what you need then you have a choice of unvented cylinder, combi boiler or heatstore cylinder. All expensive to buy and maintain.

 

[Agile]

You seem to be concerned by the efficiency of the HW cylinder but to easily dismiss not fitting a condensing boiler where the real savings are available. You dont mention the mains supply pressure and flow rate which are often limitations on the installation of unvented cylinders.

Have you really had proper advice on how you could fit one? The flexible fluing options of the Keston make it difficult to find a home where they cannot be used. And surely there is a loft where any boiler could be used with a vertical flue?

Tony Glazier

 

[MeMyselfAndI]

thanks for the replys ..
but 1: this is an open vented cylinder
2: recvery rates are from sadis tech spec,not mine
3: as stated in the post a condensor is not a viable option as the only placement avail is in loft space and condense drainage not wanted running 2 storeys down the front of my house
I am going to fit a B band system boiler and keep the cylinder, my question was only wondering why the megalifes were costed so high and if any cost savings were apparent in the long run.

 

[Agile]

Good, so the boiler can be fitted in the loft then!

You say that you dont want a condensate outlet running down the outside of your house.

Dont you have a soil pipe stack ( for the toilet ) which runs up the outside of your house, usually to vent 900 mm above the gutter. Now why dont you use that as the outlet for the condensate???

The building regs as I am sure you will know require a condensing boiler to be fitted unless its extremely expensive which would not be the case if one can be fitted in the loft and discharge to the soil pipe.

The saving from a condensing boiler will be about 40% compared with an old inefficient back boiler. That saving will dwarf any small cylinder losses.

Tony Glazier

 

[MeMyselfAndI]

the soil stack is cast iorn

 

[kevplumb]

and the point is

you can run it to cast

 

[MeMyselfAndI]

Sorry wasnt aware you could discarge to cast iorn, that said dont fancy hanging of a ladder trying to connect plastic/cast iorn addaptor

also to boot
my property is a chalet style meaning a high roof apex, plume will affect next door unless a roof kit is used. I personally dont think a condensor justifies scaffolding when a band b can be installed.
I take your point about condensors. dont want to be negative but I just dont feel its viable in this case.
most of my work is in the commercial sector roll on 2007 for the HE regs to kick in
I do value your input though

 

[Agile]

Properly sited on the roof, I dont see that pluming from a vertical terminal will be any problem to a neighbour.

As far as installation, some people manage to install terminals from inside only, I have to say I dont know exactly how just that they can.

I have installed one myself using a ladder to the eaves and a roof ladder up the slope. I dont see why scaffolding would be necessary and if added safety was required then why not a tower access platform.

Tony Glazier

 

[MeMyselfAndI]

thanks all for your comments, but the fact remains I am going to remove my 25 year old back boiler and replace using a band B rated system boiler, not a condenser as my property is exempt under the HE guidelines, does anyone have comments specifically about the original post re high eff cylinders versus conventional?

 

[Agile]

I always wonder so many people both in and out of the trade are so retiscent to use the latest technology to obtain the highest efficiency, lowest operating costs and protect the planet for the rest of mankind.

The mere fact that even if the calculations would not require a condensing boiler to be fitted under the building regulations it does not mean that there is any advantage in fitting old technology.

Tony Glazier