Plumbers/heating eng, Can u run a combi and accumulator tank??

[countrryboy]

Alright

I see there a few plumbers and heating engineers on here.

Can u plumb the supply feed to a combi from a hot water tank/accumlator??
I know combos normally work in systems with no tank, and most folk would put boiler other side to heat tank.

Looking for a system to heat my UFH, ideally with a log burner, I realise it's not ideal with the temp differences esp given the fact house will be empty for long periods throu the day.
So thought instead of having a 2nd boiler to heat a tank off water which may not be needed would be better just heating the water I need to temp i need it at, so a combi makes sense to me, but the more I have log burner on, the cheaper it will be as water hotter gong into the combi.


Renovating an old house, full rip out, floor out roof off.
Radiators would prob suit me better but the way things are going would be better just to stick UFH in incase need to use heat pumps in future
At 1 point hoped to only have the log burner as only heat source as no town gas, so means having expense of an oil or gas tank as well as the boiler

The thing is I have quite literally hundreds of tonnes off timber logged and split, think around 150m3 under cover last count up, plus heaps of logs lying all over plus cord wood and stems still to cut up.
And more trees still to come down.
Just seems crazy not to use it to heat the house.

Looked at RHI a while back and payments didn't seem worthwhile in a modern insulated house, plus the price was really scary.
Plus when u add in servicing costs and how complicated they all are.
Way house is located solar a complete waste of time, roof runs N/S and on NE side of a wooded hill ( althou not as wooded as it once was ) so gets bugger all sun apart from a few hours early morn.

Amazing how simple old back box systems were, all the rads filled by convection and gravity and no pumps needed. Bloody clever.
Now most log burners with back boilers can be dodgy putting them on in a power cut as need the pumps to get hot water away
. Would hate that stuck in a power cut with tonnes of timber and still can't put fire on.

 

[bobthedug]

From what you describe, you would probably benefit from using a heat exchanger. Heated by either your combi or/and your woodburner.
The heating circuit flow and return are via the heat exchanger. Thats a basic description of the type of system that could work in your scenario.

 

[countrryboy]

Do those big accumlator tanks not have heat exchangers inside them?

Cheers Bob.

 

[bonaparte]

 

[sikasako]

Similar to earlier comment above, my father in law uses a heat storage boiler to run his central heating system. Primary input feed is from log burner unit, with secondary input feed available from gas combi boiler ( both via heat exchangers within heat storage boiler).

Not sure whether this is the same as what you are considering, but his seems to run ok.

 

[kennyc]

pipe the accumulator from the heating flow and return on the combi, add 2 zone valves, one for the cylinder one for the rest of the heating. add a cylinder stat, and programmer and bobs the relative of your choice,any other heat sources can be fed in via extra tappings (accumulator/buffer tanks usually have an excess of these. buy one that is suitable for multiple inputs.)
if you can, get the biggest capacity you can, that way you make best use of "free" heat from solar/solid fuel sources.
to protect the combi from contamination from the woodburner, either use a cylinder with a coil or a plate heat exchanger to isolate the water circuits, as modern high efficiency boilers will not tolerate the magnetite that is usually present in mild steel/cast iron boiler circuits

 

[kennyc]

View attachment 183043

those are low loss headers, designed to hydraulically seperate circuits with seperate pumps, to prevent cross over of flow, to get one with enough capacity to be worthwhile would be far more expensive than a buffer tank /

 

[GWP]

Open fire with a back boiler fed to a tank upstairs no pump needed

 

[kennyc]

Open fire with a back boiler fed to a tank upstairs no pump needed

welcome to 1820 not going to help him with his underfloor heating though is it ?

 

[GWP]

Buy a pair of slippers then he wont have cold feet

 

[Pete6.5]

What you need is a thermal store bigger the better to a point. Yes you can heat it with a combi. Be careful when feeding hot taps with different hot water sources at the same time. (combi and thermal store) or you will blend and get warm or cold water from hot taps. And also be careful heating a terminal store with a uncontrollable heat source (log burner) or you could boil the water inside this is why the correct size store is critical. And you need a heat sink radiator working on gravity to help loose the heat in a power cut. For most times a loop with rads connected with a pump set on a high limit stat is a good idea to use the excess heat up. And always get more tappings on your thermal store than you need to future proof yourself

 

[The Singing Stalker]

Open fire with a back boiler fed to a tank upstairs no pump needed

Err, I think it is. Mine goes mad if the pump isn’t on. Or am I missing something?

 

[GWP]

Mine was a small backboiler behind the fireback control via a damper my father had a baxi back boiler and all the fireback was the boiler this had a pump for the central heating