Replacing Boilermate II with a MegaFlo

[GaytonTonner]

Hi GT,

Thanks for all your comments to date. It seems that you have a number of concerns and issues with unvented cylinders. Of course, you're perfectly entitled to your own opinion.

Is is not an opinion. It is engineering analysis backed by over 30 years of experience.

You already have a thermal store, which you have no complaints about in performance, the system is designed around that. You can replace type for type and even improve on what you have. Cheaply!

Do not go by narrow experienced jobbing plumbers. You read them here, "I only fit Vaillant and unvented cylinders and nothing", etc.

If you are insistent on fitting an unvented cylinder, against all logic, buy an direct version. Then have a combi heat it from the fresh water section. Use a brass pump, Wilo do a well priced one, and put it on the return from the cylinder (the cold feed to the combi), with a check valve after the pump.

When the cylinder stat calls for heat, the brass pumps cut in. The combi fires and heats the cylinder. The smallest DHW rated combi will do. The unvented cylinder may be smaller as the recovery rate is very fast. The combi puts the hot DHW at the top of the cylinder ready for draw off. Have decent flow combi, 13 litres or so, and use a Surrey flange at the unvented cylinder draw-off, and you will never run out of DHW. When the cylinder is depleted it reverts to what the combi can output. The brass pump creates suction in the cylinder with the water at the bottom running into the combi.

This is common practice on the Continent. It is cheap because a cheaper, smaller direct cylinder is used. I have done this with all electric houses with in place unvented cylinders when converting to a gas CH/DHW system. It is like having a storage combi, but using separate parts. An electric immersion can be fitted.

The combi will last as it only fires for continuous burns to re-heat the cylinder fast. It will not constantly switch on for short draw-off tap-turn ons, as normal combis do.

I definitely can't install a combi because of the amount of building work that would be required to plumb it in. The option you describe does sound interesting though - has anyone else seen/done something similar?

It is common on the Continent. It is cheaper to implement as well. The com,bi has to be capable of inputting hot water into the cold feed. Avantaplus, Alpha and many others can do this. You have to check.

Here is an Alpha combi heating a cylinder via the water section. The cylinder can be downsized to a very small cylinder using their method.
http://www.alpha-innovation.co.uk/custom/upload/pdf/FlowSmart Brochure 2010_FS0610.pdf

A 150 litre cylinder can be downsized to 100 litres. You do not need an expensive combi. Combis can be bought cheaper than many system boilers. You will never run out of DHW. A 100 litre cylinder will take approx 6 minutes to exhaust the cylinder at around 17 litres/min, which is a decent flow. Then it runs down to say what the combi gives which is say 13 litres/min. That is 412 litres in 1/2 hour, 802 litres in 1 hour. A 400 litre cylinder is big, expensive and heavy.

Rinnai make instant water multi-points (the best) and have packs to heat cylinders. Combis heat DHW the same way but also do CH as well - the only difference.

http://www.rinnaiuk.com/2_Products/3_Hot_Water_Storage_Packs/1_Hot_Water_Storage_Packs.html

 

[Corgigrouch]

I'm with GT.... Fit a heat bank!

Heat banks are becoming an ever increasing source of income to me as I travel round repairing them... Lots of guys in my area won't go near them as their overcomplicated systems become leaky or overheated..

I have a picture of Mr Gledhill upon my wall and I thank him every day for the bread on my table and money in my pocket..

Oh... If I was to have to put a guarantee to any installation, I'd fit an unvented, a properly sized steamer shouldn't have to cycle much at all either...

 

[GaytonTonner]

I'm with GT.... Fit a heat bank!

Heat banks are becoming an ever increasing source of income to me as I travel round repairing them... Lots of guys in my area won't go near them as their overcomplicated systems become leaky or overheated..

I don't believe you. Nothing is over complicated about heat banks. They are simple. If they leak then it is not the heat banks problem.

Look at this
http://heatweb.com/

They are taking off using Stainless steel. Any option you want is there.

Using a stainless steel heat bank using a DHW plate heat exchanger, heating the CH via a coil, keeping any sludge that emerges in the rads, and it will outlast any other other system and ensure the boiler lasts far longer as well as the cycling is eliminated and be cheaper to run.

 

[Corgigrouch]

Mmmm... All those leaky Ballofix valves on the pumps.... Perhaps the unit could be fitted on a shower tray.....