Would it be possible to fit an Unvented Hot water Cylinder off a Combi Boiler (both in loft) just to supply a bath and shower? I could zone of the cylinder from the heating side so only heating this Cylinder when hot water is req from it?
Unvented water off a combi boiler?
- Thread starter clarkerothwell
- Start date
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yeah thought so, just best to get second oppinion, cheers.
B
BigBurner
Why? If the combi is not delivering enough DHW, then upgrade to a high flow model - or another combi. It will be no more expensive that fitting an unvented cylinder that requires an annual service charge.
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Nothing wrong with a 'Y' plan, but you will have to fit the supplied 2 port as well on the hW flow to the cylinder.
Hopefully the regs will be updated to soon to allow the 2 port not to have to be used as the safety device.
About time this antiquated rule was removed with modern boilers.
Hopefully the regs will be updated to soon to allow the 2 port not to have to be used as the safety device.
About time this antiquated rule was removed with modern boilers.
B
BigBurner
If you insist on an unvented cylinder (you need an annual service charge) , buy a direct model which is cheaper than one with a coil. If the combi 3-way valve is electric.
Connect the cold inlet to the combi to the bottom of the cylinder.
Connect the DHW outlet to the top of the cylinder.
Fit a bronze pump on the pipe from the bottom of the cylinder pumping into the combi. (available cheap from ebay) The Willo is £50.
Connect the bronze pump to the cylinder stat.
When the cylinder is cold the pump energises and pumps into the combi. The combi heats the fresh water and pours a minimum 24kW into the cylinder. Reheat is super fast.
No zone valves and very simple and a super fast reheat. The bronze pump can be off a programmer to time usage. Also when the cylinder is exhausted of heat the DHW will revert to what the combi will supply. You never run out of DHW.
Fitting an unvented cylinder to supply water to washing areas and existing combi to supply hot water to kitchen gives you best of both worlds. If combi fails, like they often do, you do not start smelling for lack of hot water to wash.
Until recently, I has a Vaillant VCW 242 with two heat zones and one HW zone.
Until recently, I has a Vaillant VCW 242 with two heat zones and one HW zone.
Can BB explain how he connects the cold water into this system he is recommending? I can't see why, when the cylinder is cold, the hot water from the combi isn't blended with mains cold and is therefore swamped with cold.
Also, I am surprised for one with such strong views on how 'dangerous' unvented cylinders are, he is proposing on an internet forum that someone fits this set up which doesn't have G3 approval and will not meet building regs.
The stored water is over 15 litres, there is no overheat thermostat on the storage cylinder and no way to stop the water from the combi (eg: zone valve).
Lastly, some combis would not tolerate the high temperature recirculated water coming in their cold input.
This type of posting is the work of a fantasist and could result in someone innocently wasting a small fortune building someone else's pipedream. It has been posted with the normal swagger and implied gravitas but is no more than a project from someone with an over developed imagination.
If you want to build Meccano models, BB, use your own toys don't get other people to pay for them. Get your system working (I'm not saying it can't work, by the way) and then list the actual boilers you have successfully used the same configuration on.
Otherwise you are being irresponsible.
Also, I am surprised for one with such strong views on how 'dangerous' unvented cylinders are, he is proposing on an internet forum that someone fits this set up which doesn't have G3 approval and will not meet building regs.
The stored water is over 15 litres, there is no overheat thermostat on the storage cylinder and no way to stop the water from the combi (eg: zone valve).
Lastly, some combis would not tolerate the high temperature recirculated water coming in their cold input.
This type of posting is the work of a fantasist and could result in someone innocently wasting a small fortune building someone else's pipedream. It has been posted with the normal swagger and implied gravitas but is no more than a project from someone with an over developed imagination.
If you want to build Meccano models, BB, use your own toys don't get other people to pay for them. Get your system working (I'm not saying it can't work, by the way) and then list the actual boilers you have successfully used the same configuration on.
Otherwise you are being irresponsible.
B
BigBurner
Not a very bright idea. Both supply DHW at mains pressure, so no advantage. Best have the combi heat a direct cylinder as I explained in a post on this thread. An electric immersion can then give DHW backup. The combi then only fires to reheat a full cylinder and is not on-off all day, when kitchen tap use it, so less use of the combi and parts last far longer.
Combis do not always break down. Quality models do not.
B
BigBurner
It is plain you can't understand something so simple. The cold feed to the cylinder is at the bottom, us usual, and the DHW draw off is at the top, as usual. The combi acts like a pumped circulator only. It only comes on when the cylinder thermostat calls for heat and the bronze pump kicks in.
The combi will deliver 60C of heat and dump it directly into the top of the cylinder. The cylinder heats top down. The return (cold inlet) to the combi will always be cool due to cylinder stratification. The re-heat is very fast as all the boilers heat is dumped into the cylinder. When the cylinder is exhausted of heat the DHW delivery will revert to what the combi can deliver - you never run out of DHW.
It is similar to the McDonald PlateFlow cylinder.
http://www.mcdonald-engineers.com/products/plateflow_specs.htm
The difference is that the plate is inside the boiler casing not external. In a combi. Where does the fresh water travel? Through a few pipes, passing a flow switch and through a plate heat exchanger and out. Got it? Simple isn't it?
Now you know.
Using any combi with a flow switch and plate heat exchanger, as most have, will do, with no adverse effects.
This can be done on an unvented or open vented cylinder. Connecting a combi onto an existing unvented cylinder does not require G3. No more than exchanging an immersion in an unvented cylinder, or connecting the DHW outlet.
One job had a direct unvented cylinder in an all electric house. The owner wanted a gas CH system as electric was cumbersome and expensive to run. The best way was a cheap 24kW combi to do the CH on weather compensation, and the DHW water section heating the existing cylinder directly. A Surrey flange was used in the 1" top DHW port to connect the DHW combi outlet. Worked a treat.
Can you post a simple drawing of this BB, showing the pipe connections inparticular the cold mains connection.
B
BigBurner
I have already described it. Draw it out. Think of the combi as a water heater. The cylinder connected up as normal.
- A pipe from the bottom of the cylinder to the combi inlet - a bronze pump on this pumping into the combi.
- A pipe from the DHW outlet of the combi to the top of the cylinder.
- The cyl stat switches the pump. Better have two cyl stats (with relay) to prevent combi cycling (same with any cylinder really)
- Combi only comes on to re-heat in one long efficient burn. Your never run out of DHW.
Simple and highly effect...and cheap as combis are a cheap item - you only need a 24kW. The combi may only come on one or twice a day to heat the cylinder, promoting longevity of the combi as the DHW components are used far less. If a long shower is had and the cylinder exhausts of DHW the DHW flow reverts to what the combi can provide at a lower flow rate. Two stage flow rate.
The only extra is a £50 bronze pump, used about twice a day.
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