Changing from vented to unvented system

[danieljamesscott]

Hi,

I'm having my central heating/hot water system updated. The existing system is an ancient potterton boiler and vented cylinder. I want to change to a new boiler and unvented cylinder.

It's a 2 person, 4 bed mid-terrace property with 8 radiators, one bathroom, one shower room and a cloakroom.

The engineer has recommended an 18kw system boiler and 150l indirect gledhill cylinder. Do these sound reasonable?

My only concern is that the existing cylinder is fitted in a cupboard in the eaves of the roof and the space is quite tight. We've discussed several possibilities.

1. Fit the 150l cylinder in the same location. The cylinder may have to move further into the room which would mean that the cupboard would need expanding/boxing. The ceiling has already been cut away to make room for the existing unvented cylinder.
2. Fit 2 90l cylinders which are small enough to fit into the cupboard.
3. Fit a 180l horizontal cylinder.

Can anyone help with the advantages/disadvantages of these possibilities? I'm leaning towards a 180l horizontal cylinder, but I don't know if there is a significant difference from vertical cylinders? I read that they're less efficient, but that would be OK if the difference isn't too great.

The 2 x 90l cylinders is a nice idea, would this mean 2 expansion tanks too? Would this increase complexity? I guess there are 2 cylinders to go wrong, but maybe we would have added redundancy since we could manage with one if there was a problem with the other?

Let me know if you need more info.

Thanks,

Dan

 

[Dan Robinson]

Vertical over horizontal every time.

 

[danieljamesscott]

Why?

Efficiency?
Reliability?
Other reason?

 

[stardanny]

Vertical cylinder stored more hot water than horizontal.

Daniel.

 

[danieljamesscott]

Vertical cylinder stored more hot water than horizontal.

Daniel.

Sorry, I don't understand what you mean. The capacities are the same 2 * 90 or 1 * 180. The other was 150, so the vertical stores less than the horizontal, not more.

 

[dcawkwell]

glow worm ultrapower a cross between combi and unvented cylinder.
Will outperform a 300 litre cylinder and all in the nice one package.
Job done.

 

[danieljamesscott]

glow worm ultrapower a cross between combi and unvented cylinder.
Will outperform a 300 litre cylinder and all in the nice one package.
Job done.

Looks like a nice combination system, but I have no room for this. Also, I've had several bad experiences with Glow-Worm boilers.

 

[ALCPlumbing]

Personally I would go with two upright cylinders if they don't eat into the room. It is more complex but that's for the plumber to worry about. Make sure he knows how to do this as I've come across some shocking jobs where they've used two cylinders but not done the job properly.
You also need to check that you're incoming main is sufficient in terms of pressure and flow rate. You will possibly have to upgrade the rising main as well as 15mm isn't sufficient.

 

[danieljamesscott]

Personally I would go with two upright cylinders if they don't eat into the room. It is more complex but that's for the plumber to worry about. Make sure he knows how to do this as I've come across some shocking jobs where they've used two cylinders but not done the job properly.
You also need to check that you're incoming main is sufficient in terms of pressure and flow rate. You will possibly have to upgrade the rising main as well as 15mm isn't sufficient.

OK, thanks. Is there a reason for the dislike of horizontal cylinders? I have no experience, but a horizontal cylinder seems a perfect solution to my problem.

My plumber doesn't have a particular dislike of the horizontal model. He's fine with two cylinders too, he's said that it's no problem and he's done them before. Is there anything special I need to watch out for?

Pressure and flow look good on first glance, but I'm going to do some more tests before we go for it. I could always upgrade the main after, right? We might have poor flow for a while, but it's not catastrophic if there isn't enough? We'll be replacing our kitchen in a few months, so will have the chance to upgrade the pipework at that time.

Thanks for the information.

 

[ALCPlumbing]

As the cylinder is heated from the bottom and this is where the stat is the height allows hot water to rise and by the time stat is satisfied the majority of the tank is hot. You dont have the height to with a horizontal tank and you wont get as much hot water.

 

[ALCPlumbing]

Another way of putting it is that you have a higher volume of water below the stat as its horizontal. One I fitted before had the stat half way up so half the water will be under temperature. The stat is probably a fifth of the way up on a 90ltr upright.

 

[dcawkwell]

glow worm ultrapower a cross between combi and unvented cylinder.
Will outperform a 300 litre cylinder and all in the nice one package.
Job done.

Looks like a nice combination system, but I have no room for this. Also, I've had several bad experiences with Glow-Worm boilers.

Ultrastore as next best it has two 25 litre tanks in the back.
Buy with lifetime warranty 15 years piece of mind.

 

[brownexcel]

Hi there

Have you ever considered a thermal store, rather than an unvented cylinder?
You can always contact manufacturer like Range, Gledhill, Mac Donalds.
They can assist what capacity is sufficient for your home.

Regards

Michael eng tech

 

[danieljamesscott]

Have you ever considered a thermal store, rather than an unvented cylinder?

I hadn't considered this, and they do look good, but as I said, I'm limited for space and it looks like thermal stores are far larger than I have room for.

Anyone have any more input on horizontal vs vertical? The only point mentioned so far is the thermostat location, which I agree is not optimal, but may be countered by altering the thermostat a little.