New Combi or Unvented Cylinder

[picasso]

Poor pressure through out the house (unless you put a pump in) dead things in the loft tank if the lid gets knocked, frozen pipes in the loft that flood your house when they thaw,

versus

Clean fresh water at all taps, good pressure for shower / quick bath filling and no pipes in loft, quite surprised your not recommending lead pipes and outside toilets.

 

[vulcancontinental]

Poor pressure through out the house (unless you put a pump in) dead things in the loft tank if the lid gets knocked, frozen pipes in the loft that flood your house when they thaw,

versus

Clean fresh water at all taps, good pressure for shower / quick bath filling and no pipes in loft, quite surprised your not recommending lead pipes and outside toilets.

Fortunately I've been able to avoid every single one of the negatives in the first paragraph (pipes in a loft is not a negative) and have all the positives in the second with absolute zero maintenance for 40 years, 35 living there myself and 5 now with my son living there.

I dont know anything you dont know.

 

[picasso]

So your system was installed before unvented cylinders were allowed , no one would expect you to rip out a serviceable cylinder for no reason but there will always be luddites.

 

[bernardgreen]

but there will always be luddites.

Deciding to install a vented cylinder is not being a luddite. There are valid reasons to have a vented cylinder supplying low pressure water.

What is needed in a bathroom, high pressure or high flow. High pressure at the wash basin taps can mean water jetting into the bowl and then splashing out of the bowl, not to mention the wear and shorter life time of high pressure tap inserts.

 

[ddsull]

I'm happy with Unvented option as I really miss pressure from my last house. Also taking out tank in the loft frees up more storage space and the ability to extend (i.e. not having to take out new plumbing) is a plus for me.

Does anyone know if it's only G3 certification for an unvented cylinder? Seems to be a bit different in Scotland where I'm based (as no mention of it in the buildings regulations). I'm presuming there are other accreditation bodies?

 

[vulcancontinental]

So your system was installed before unvented cylinders were allowed , no one would expect you to rip out a serviceable cylinder for no reason but there will always be luddites.

That's valid and you bring up a good point; I got my unvented ticket in I think 1992, I have it at home. About that time I wondered about swapping for an unvented cylinder, there were no issues, I just pondered because I had my new ticket but I couldn't ignore the fact that I hadn't had a problem and still haven't even touched the DHW cylinder, CWS cistern, gate valves etc since it went in (yes the GV work or did when I last checked as I crack them back a little from full on and they're not Prestex either).

I can't help but suggest an unvented cylinder with the accessories would have needed a lot of servicing or parts replaced or cleaned in the 30 years since 1992 or so. If it was glass lined it would have been changed and if an early Magaflo I'd have had a partially filled cylinder because the early ones didn't have the non-effective baffle so I'd have had to add an expansion vessel. Probably had to swap out the high temp MV too (I certainly have had to swap out the regular MV's.

I'm a strange Luddite I reckon, I'll happily fit unvented for those who want one, why not, they're my customers and i'll go back and service them and replace parts too.

The question is that if I'd moved to a property that was suited to stored DHW, I have a combi, which would I have chosen, vented or unvented? Before writing this and answering a similar post recently I'd have said unvented without thinking but now, if the situation suited and now I've thought about it, I'd stick with stored CW and a vented cylinder.

If I'd have kept the Netaheat 10/16 it'd still be there chugging but I wanted to try the new condensers so Trisave, Glow-Worm Energy Saver, Baxi and now Vokera, all to save perhaps 15% on NG at around 4p a kW until recently.

The Honeywell AQ6000 energy manager still going strong.

 

[ddsull]

I've decided on a Heatrae Sadia Megaflo Eco 250SI Unvented Indirect Solar Cylinder. I want the solar option so I can future proof it. My plumber recommended this as being a really good cylinder with the expansion tank built in etc. (get what you pay for etc.).

Now the 250 litre (which is what I want) is about £1870. However, I found the 300 litre version for £120 cheaper. Would it be overkill to put it in? The house is currently 4 beds two baths but will probably be 5 bed 3 baths (add an ensuite) when completed. Would it cost a lot more to heat the 300litres conventionally (will be solar add on in the future) or should I stick with the 250 litre?

Any thoughts suggestions gratefully accepted.

Thanks

 

[vulcancontinental]

I've decided on a Heatrae Sadia Megaflo Eco 250SI Unvented Indirect Solar Cylinder. I want the solar option so I can future proof it. My plumber recommended this as being a really good cylinder with the expansion tank built in etc. (get what you pay for etc.).

Now the 250 litre (which is what I want) is about £1870. However, I found the 300 litre version for £120 cheaper. Would it be overkill to put it in? The house is currently 4 beds two baths but will probably be 5 bed 3 baths (add an ensuite) when completed. Would it cost a lot more to heat the 300litres conventionally (will be solar add on in the future) or should I stick with the 250 litre?

Any thoughts suggestions gratefully accepted.

Thanks

I don't know what part of the country you're in but in some areas the water will absorb the air forming the expansion space 2 or 3 times a year in spite of the baffle. (I'm in Beds/Herts area). This means recharging it and sometimes the temp/pressure relief valve will need maintenance. Download the instructions to see Megaflo advice on how to recharge the air gap. Ask if the installer can refer you to other megaflo installs in the area to see whether they've had the same issue, it may not be relevant to you. I've had to fit external vessels to megaflo's because of this but it means the cylinder is used not fully flooded. Oso stopped using the drop tube method because of this.

 

[ddsull]

I don't know what part of the country you're in but in some areas the water will absorb the air forming the expansion space 2 or 3 times a year in spite of the baffle. (I'm in Beds/Herts area). This means recharging it and sometimes the temp/pressure relief valve will need maintenance. Download the instructions to see Megaflo advice on how to recharge the air gap. Ask if the installer can refer you to other megaflo installs in the area to see whether they've had the same issue, it may not be relevant to you. I've had to fit external vessels to megaflo's because of this but it means the cylinder is used not fully flooded. Oso stopped using the drop tube method because of this.

Thanks for this. I'm in Edinburgh Scotland. Is it an issue with hard water that it would cause this issue. The water up here is soft so if hard water causes the issue then it should be OK?
Would you stay clear of a Megaflo? What would you recommend instead. I had an Albion Ultra steel which was faultless for 10 years.
Also 250l or 300l?
Thanks again

 

[Johntheo5]

I've decided on a Heatrae Sadia Megaflo Eco 250SI Unvented Indirect Solar Cylinder. I want the solar option so I can future proof it. My plumber recommended this as being a really good cylinder with the expansion tank built in etc. (get what you pay for etc.).

Now the 250 litre (which is what I want) is about £1870. However, I found the 300 litre version for £120 cheaper. Would it be overkill to put it in? The house is currently 4 beds two baths but will probably be 5 bed 3 baths (add an ensuite) when completed. Would it cost a lot more to heat the 300litres conventionally (will be solar add on in the future) or should I stick with the 250 litre?

Any thoughts suggestions gratefully accepted.

Thanks

It will take ~ 2.9kwh to heat that extra 50 liters, assuming 7C/kwh gas cost and boiler efficiency of 80% extra cost will be ~ 25C. The heat loss will be slightly higher, using a ancient calculation the 300 liter cylinder might lose 3.98kwh/day or 0.48degC/hour, the 250 liter may lose 3.56kwh/day or 0.51degC/hour, extra loss 0.42kwh/day or say 4C/day which is the real extra cost of running 300 liter cylinder.
Also since Solar heating is being considered I would go for the 300 Liter.

 

[ddsull]

It will take ~ 2.9kwh to heat that extra 50 liters, assuming 7C/kwh gas cost and boiler efficiency of 80% extra cost will be ~ 25C. The heat loss will be slightly higher, using a ancient calculation the 300 liter cylinder might lose 3.98kwh/day or 0.48degC/hour, the 250 liter may lose 3.56kwh/day or 0.51degC/hour, extra loss 0.42kwh/day or say 4C/day which is the real extra cost of running 300 liter cylinder.
Also since Solar heating is being considered I would go for the 300 Liter.

Many thanks John. It took me a minute work out the C/kwh then I realised you're in Ireland/Cork! I'm a Cork man myself living over in Edinburgh so nice to get advice from another Cork man!
Yeah I think if I go with Megaflo then the 300 litre tank is a no brainer as cheaper to buy and I have the room to install it. And with the addition of Solar down the line it will be (hopefully) future proofed.

 

[MeldrewsMate]

There seems to be an off-topic discussion going on here re the virtues of vented vs. unvented. Both have their pros and their cons, but the OP has already decided on 330 litre Megaflo. Suggest that row gets punted over to a new thread.

OP, you may be tempted (by others) to go for the 'solar' version of the Megaflo. With that you'll be paying handsomely for an extra heating coil, and its usefulness depends on whether you opt for solar thermal or solar PV on the roof. IMO solar PV wins hands down if you have the roof space in which to fit it; the electricity it produces can be easily diverted to your cylinder's immersion heater automatically, there is much less maintenance with solar PV, and it costs less to install. Solar thermal has had its day on all but the smallest of roofs.

 

[vulcancontinental]

Thanks for this. I'm in Edinburgh Scotland. Is it an issue with hard water that it would cause this issue. The water up here is soft so if hard water causes the issue then it should be OK?
Would you stay clear of a Megaflo? What would you recommend instead. I had an Albion Ultra steel which was faultless for 10 years.
Also 250l or 300l?
Thanks again

I can't advise I'm afraid, water is so changeable or used to be, there's more of a grid now. I found in north east Herts I'd lose the bubble, several miles west it didn't happen, the water came from an artisean well in a different area. I think I'd look at Oso and I hear people recommending Joule but have no experience of them personally.

 

[Johntheo5]

This bubble must be taken into account when sizing your HW cylinder. For example a 300 Liter cylinder will only have a effective volume of ~ 265 liters assuming a cold water pressure of 2.5Bar and allowing the cylinder pressure to rise to just over 5Bar after heating to 60C from cold. A 250 liter cylinder will have a effective volume of 220 liters under the same conditions. All this is assuming that the bubble is created at atmospheric pressure by opening the cylinder PRV and allowing drain down until no more water coming from PRV which I think is the normal way of creating this bubble?. Be interesting to see where (height wise) the PRV is located.

Correction, those numbers should be 290 liters and 240 Liters so not a big deal.

 

[ddsull]

This bubble must be taken into account when sizing your HW cylinder. For example a 300 Liter cylinder will only have a effective volume of ~ 265 liters assuming a cold water pressure of 2.5Bar and allowing the cylinder pressure to rise to just over 5Bar after heating to 60C from cold. A 250 liter cylinder will have a effective volume of 220 liters under the same conditions. All this is assuming that the bubble is created at atmospheric pressure by opening the cylinder PRV and allowing drain down until no more water coming from PRV which I think is the normal way of creating this bubble?. Be interesting to see where (height wise) the PRV is located.

Correction, those numbers should be 290 liters and 240 Liters so not a big deal.

Thanks for this. I called up OSO to enquire about the twin coil version of their cylinder and they say they are phasing out the twin coil as the demand has dropped. The technical guy recommended just getting a standard cylinder and using PV to heat the water via the immersion when required in the future. To be fair not sure when we'd get the solar on as need to do the extension first. It also gives the option of a better energy rated cylinder A rated (just 1.18 kw/h/day heat loss). The megaflo is C rated with 1.84 kw/day heatloss. Not much difference but would add up to round £20 a year.

Might be the most straight forward option.