Back boiler with stove - yes or no?

darkstream

We are in the middle of a new build and the heating for the house will be ufh on the groundfloor and radiators on 1st floor run by a condensing oil boiler. Building regs also stipulate that we'll need solar panels which will also be connected up to a 305ltr cylinder. The thing is that we'll have a stove in the living room for which I wanted to connect to a back boiler so as we'll not be totally dependent on oil but the builder says that will take away from the efficiency from the condensing oil boiler. He advises that we just use the stove for heating the room, rather than the radiators as well which I had in mind.

Anyone else any views on this?

cabledude

I'd ask him to explain to you how exactly fitting a boiler stove will reduce the effecency of a condensing boiler. I have both and didn't see any reduction in effecency of the boiler. They are two different heat sources that work independent of each other. I have heard that not all builders are interested in fitting stoves.

Also I wasn't aware that building reg's stipulated solar panels....

darkstream

He mentioned something about it creating too many bubbles( I presume he meant in the water cylinder if both were on together). It was something I couldn't get my head around either as I've heard of cylinders with double or treble coils for heating but there again my knowledge on these matters are somewhat limited along with all the other things I'm trying to get my head around on a self build . I do share your scepticism on whether he wants to put one in, though.

Apologies for any confusion but I was cutting to the chase, they don't specify solar panels but a renewable energy source which is solar panels in our case.

But good to know you have both in and everything going ok. Thanks for you help, cabledude.

cabledude

Too many bubbles????

In fairness a stove with a boiler is the same thing as an open fire with a back boiler and people have been using this type of dual set up for years. Tell him that you want a bioler stove and that yu are not going to be persuaded. It's up to him to find a way to minimise the bubbles!!!

Billy Bunting

Tell him to stick to the building and get someone (hopefully your plumber) with a heating background to advise on the heating.

Outkast_IRE

If funds arent tight i would hook the back boiler,solar and condensing boiler up to a buffer tank , this tank then can be used to heat where its needed the underfloor or the hot water cylinder . If i was building my own house tommorow its the main thing i would consider

darkstream

Thanks Outkast. Will definitely consider the buffer tank option

bobbuk

I was going with the exact same set up as you, but plumber has come back and suggested the buffer tank instead. slightly more expensive but apparently streets ahead of the previous option (not just my plumbers opinion).

freddyuk

Here is what I have just installed -

I have been planning a system for sometime which would be based around a solar thermal panel and WBS gravity system. After a false start trying to get a gravity system to work horizontally I have now got results which I think are reasonable.

Target was to have solar hot water during the day and as much of the year as possible and when the WBS was lit I wanted a “free” tank of hot water being generated with excess going to a radiator or two so as to back up the oil boiler.

Property is 1980 block bungalow with a standard twin coil 36 litre DHW cylinder on ground floor. A 5kw clearview WBS is in the middle of the property and 42 x 58mm solar EV tubes on a south facing roof.

A 200 litre stainless pressurised (open vented install) tank is installed right above the WBS in the attic. The tank has two coils with 3/4 inch connections. It has two sensor pockets. I have a 300 litre but the headroom is insufficient.

Plan was to feed the solar into the lower coil as normal. Then feed the WBS into the top coil with an open vent to standard FE tank with a pipe stat and overheat radiator pumped circuit. I would then feed the hot water down to the lower DHW tank via the second coil on the lower DHW cylinder via an indirect pumped circuit. I decided that the WBS, which was plumbed in 28mm, would not like being forced though a 3/4 inch connection and possibly a coil of the same size, so I repiped it to put the WBS circuit into the top of the 200 litre tank directly though the 3/4 inch boss for the anode rod so there was little restriction and then take the return from the bottom of the buffer tank via the cold inlet boss.
The top coil was then used to feed an indirect circuit down to the second coil in the DHW tank with a pump and pressure vessel.

The controls were standard solar pump station with a bypass over heat via a diverter valve and small radiator in the attic.

A pipe stat on the WBS hot pipe would run a pump via radiator downstairs in the event of overheat. No other controls on this circuit.

Two sensors on the buffer tank for the solar circuit T2 and T3.

I then installed a temperature differential switch with a sensor 1/3rd down from the top of the buffer tank and a second sensor 1/3 down the DHW cylinder.This then pumps hot water to the lower tank when there is an 8c difference. A thermostat on the lower tank will switch off the transfer circuit if the lower tank reaches capacity.

If the system is still heating then the buffer will trip the bypass circuit for the WBS. It is unlikely that we will generate enough excess heat to risk the system overflowing but the FE tank is fibreglass with a copper ball float.

If the transfer circuit thermostat fails then the lower DHW cylinder is open vented so will overflow as it should. The only sealed circuit is the the solar and the transfer and both have expansion vessels and prv.

I have fired up the WBS with coal to get it really hot. The temperature in the 200L buffer got to 75c on T2 and 72c on T3 so the tank was getting hot all the way down after about 4-5hours (a standard evening by the fire). The differential switch worked and heated up the DHW cylinder to about 55c on the thermostat (lower part of the tank).
There seems little stratification within the buffer as obviously the WBS is going from top to bottom but as the transfer circuit is indirect the pumped water is not affecting the stratification at all.

So it all seemed to work as it should. The solar was intermittent as we had very little sun to test it fully but it feeds in hot water as and when it is up to temperature which was 60c at the panel on a cloudy but bright day.

I need to tweak the sensor positions and the temperature settings to make sure we get the maximum amount of benefit but I am quite pleased with results to date.

I now need to get some real time measurements to ensure we are seeing the correct numbers so some digital pipe stats and additional sensors will be installed.

Even if the oil boiler comes on it is heating warm water so will be on for 5 -10 minutes for basic DHW needs. Have a bath early evening if the WBS is on!
Any comments appreciated.