Relative cost of heating fuels

[gdal]

Renovating very old stone house in Oxfordshire. Insulation will be…ok. New windows, doors, double glazed. Loads of insulation in the loft. Solid walls 400-500 m thick. Underfloor heating in limecrete floor. Radiators upstairs. Two showers, two occupants. No mains gas and no room for LPG tank. So we are going for oil fired boiler. Can’t do a heat pump
 

But now I’m thinking is it mad? Price of fuel oil seems wildly volatile and although I believe it will settle down, it could settle down at £1.50 per litre? Should I get an electric boiler ( since the world is going crazy )

 

My amateur sums tell me that a litre of oil has about 10KWh of energy. If the boiler is 90% efficient, and the price is £1.50/litre that means that I’d be paying about 17p/KWh. Cheaper than the new price cap of 28p for electricity.  
Am I thinking straight? Would be a first haha

 

[ProDave]

Why can't you do a heat pump?  At a COP of it 3 would be about 9.3p per kWh

[gdal]

51 minutes ago, ProDave said:

Why can't you do a heat pump?  At a COP of it 3 would be about 9.3p per kWh

Nowhere good to site it. Noise. Wouldn’t get us warm enough as the house is not super well insulated and this can not be improved. Neighbours have had poor experiences.
I need to burn something. Gas isn’t an option that leaves oil, electricity or just bags of ££££ 

[Iceverge]

Yikes, can you super insulate? £5k of extra insulation will last forever. £5k of oil will dissappear very quickly. 

 

At the very least price triple glazing. €800 to go from 2g to 3g for my neighbours bungalow.

 

The UFH is your issue here. Slow responce time as it heats the structure and in a high heat loss house it'll use a lot of energy. Get a split A2A heat pump to heat just the air quickly when you need it. ( small outdoor unit, can be wall mounted) .You can get through the wall ones but the COP isn't as good. Consider an exhaust source heat pump all in one unit for DHW. Is solar PV a choice?

 

You could run the UFH on a willis heater to a much lower temp just to make it more comfortable underfoot but not really to heat the house. 

Edited March 21, 2022 by Iceverge

[SteamyTea]

1 hour ago, gdal said:

Nowhere good to site it. Noise. Wouldn’t get us warm enough as the house is not super well insulated and this can not be improved. Neighbours have had poor experiences.
I need to burn something. Gas isn’t an option that leaves oil, electricity or just bags of ££££ 

If you can get an oil tank in, you can get an ASHP in.

They are not noisy if sized correctly.

The house does not need to be 'super insulated', which has no actual description/meaning.  If the ASHP is sized correctly it will heat the place.

Was your neighbours sized correctly.

 

Can you spot a common theme in my responses?

[Nickfromwales]

Get a much smaller oil tank and a hybrid ASHP   Best of both worlds.

Grant Vortexair

[saveasteading]

1 hour ago, Iceverge said:

£5k of extra insulation will last forever. £5k of oil will disappear very quickly.

I like that.

[saveasteading]

53 minutes ago, SteamyTea said:

They are not noisy if sized correctly.

I have heard some very noisy ones , but I don't think they were thoughtfully installed.

They are clearly becoming quieter too.

 

Although it is essential to have lots of free air around the heat pump, if there is plenty of room, a fence could be built around it that combines free air flow with acoustic dampening.  

Hedges too? I would think so.

[CotswoldDoItUpper]

If you can get in an oil tank in, you can get an LPG tank I’m sure. They can also be buried. 

[Nickfromwales]

2 hours ago, saveasteading said:

I have heard some very noisy ones , but I don't think they were thoughtfully installed.

They are clearly becoming quieter too.

 

Although it is essential to have lots of free air around the heat pump, if there is plenty of room, a fence could be built around it that combines free air flow with acoustic dampening.  

Hedges too? I would think so.

Having just installed one for a client, I can confirm that they are VERY quiet indeed. When commissioning it I was getting frustrated with the controller as I couldn't get the thing to kick into life. Stuck my head out the front door, nothing, back and forth and so on for a good couple of hours. Then the client said "but Nick, the pipes are all hot?"  I walked up to it and was met with a breeze of Baltic cold air coming from the fan, and a very faint whirr. It was indeed up and running, and had been for some time, I just genuinely couldn't hear it running from the front door. Unit was the opposite corner of the driveway at the front of the property. Client and neighbour able to have a polite conversation whilst it was running under their noses, with no mention of nuisance noise from the neighbour.

 

Design and foresight is paramount to success here, but it would be fair to say that was in a 'low energy-highly insulated' dwelling vs what we have here. That said, it would be realistic to assume any heat pump for this ( @gdal's ) application would not be anywhere near as quiet when the depths of winter descend, so some serious thought needs to go into this decision for sure.

 

For my current clients I have designed a "fence" which is a) a visual barrier, and b) an effective acoustic baffle, plus that promotes near-free airflow ( my design has been accepted by the manufacturer so the warranty is still good, even though it is closer to the front of the HP than the MI's would suggest is permissible ) so indeed this is a good option to 'direct' any identified nuisance sound to where it is not going to be problematic. For another, I have suggested a galv 'cage' with planters at the base, which will then become a living acoustic barrier, spaced accordingly so it can be maintained from both sides for trimming.

 

The noisy ones have just been installed in ignorance AFAIC, and some just shouldn't have been an option at all, eg as they were simply unsuitable due to the ( expected ) unacceptable levels of noise pollution. This isn't just a client consideration, as most do not want to piss their neighbours off either.

 

Measure twice......

Edited March 21, 2022 by Nickfromwales

[Marvin]

Once again a lot of sense from @Nickfromwales 👏 

 

Our ASHP was installed on the flat roof about 8 month ago. Neighbours noticed box but no noise issue, not even over the winter when its supposed to be noisiest as the ASHP works hardest to heat the property. 

 

If there is a lot of noise there has to be something wrong with the sizing or positioning of the ASHP or the actual ASHP, or the way it's being used. Stick a car in second gear and do 50mph and that makes noise and eat fuel, so it the car crap?  

 

However, its worth considering all the AIM and APE elements before making decisions. That is Airtightness, Insulation, Mechanical Ventilation with Heat Recovery, and Air Source Heat Pump, Photovoltaics and Electric Vehicle.

 

Some of these will not work properly without the others:

 

1. A MVHR will not work properly without Airtightness.
2. An Air Source Heat Pump will have to compensate for the lack of Airtightness and Insulation to the degree that the benefits become questionable, especially during winter, without them.
3. An ASHP uses electricity and Photovoltaics can supply a little during winter and a lot during summer when cooling can be a problem and an ASHP can supply cooling.
4. PV can supply a little to an Electric Vehicle during winter and plenty during summer if your vehicle is at home during sunny days.
5. Extending a property and only doing AIM works to the extension will be no good, you have to do all the property within the thermal envelope.  

So if finances cause you to have to consider only a few in my humble opinion AIM first and go APE later. (but prepare the property for the APE works as much as you can).

 

There are exceptions to properties which have AIM whereby the insulation is so thick that heating becomes a minor issue!

 

Best of Luck

 

Marvin

 

[saveasteading]

8 minutes ago, Marvin said:

installed on the flat roof

Does it have acoustic bearings/pads? It could otherwise set up a hum through the joists.

 

42 minutes ago, Nickfromwales said:

I have designed a "fence"

How far away?

I would hazard that it depends on whether the expelled cold air is horizontal or vertical, as it needs to be got rid of, but fresh air can come from all around. 

 

My thought on the fence construction is to use horizontal planks, hit and miss on opposite sides, as this is the basis of some motorway acoustic fencing.

[Nickfromwales]

33 minutes ago, saveasteading said:

How far away?

I would hazard that it depends on whether the expelled cold air is horizontal or vertical, as it needs to be got rid of, but fresh air can come from all around. 

 

My thought on the fence construction is to use horizontal planks, hit and miss on opposite sides, as this is the basis of some motorway acoustic fencing.

800mm in front of the unit. All other clearances are as per MI’s eg 300mm rear for fresh energy-rich air to get to the unit without issue. 
This particular one will have 15x200mm tanalised planks mounted vertically at 30 degrees off perpendicular, set out around 150-200mm apart. Basically a balustrade standing 1200mm high, encompassing the HP’s all 3 sides round, and set out so when viewed from the most common angle all (3) heat pumps cannot be seen, ( unless you stand more-or-less in front of them ).
 

As far as what the HP ‘sees’ there is almost zero resistance or impact of airflow as the ‘blades’ of the timber ‘baffles’ are near perpendicular to the direction of airflow. 
 

I would not do the hit n miss ‘fence’ as the timbers will offer direct resistance and a lot of that air will get buffered back causing noise and reducing flow / affect performance of thr HP. 

Edited March 21, 2022 by Nickfromwales
Tanalised vs tantalised 🤣

[saveasteading]

Log burners:
Building inspector has asked for more detail, so for anyone who doesn't know, as I have just learnt....

 

As earlier discussion, the  air intake is needed and mandatory for a modern (airtight) house.

It can be an inlet placed near the stove, but I have gone off that idea, as most stoves now seem to have rear inlets for direct air.

A 5kW burner needs a 60mm piped supply. There is no mention of length of pipe, and any friction losses along the way.

The manufacturers seem to only provide an adaptor to the back, where I had expected an optional kit for appearances and strength.

The utilitarian spiral bendy pipe seems to be the standard solution but will look horrible behind the stove, and I wonder about cleaning damage.

 

I have come up with a solution for our circumstances. The feed needs to be brought in early so have allowed for  pvc drain solution under the wall, and then the slinky pipe can go in, just in time.

Needs something better at the back of the stove but this will do for now. Not a pvc pipe obviously, but perhaps keep our eyes open for something sturdy to replace or enclose it. For example if KeeKlamp made 60mm or greater id (their biggest is 60od).

 

My sketch is attached.....I am no draughtsman. Not looking for comments although they are welcome of course. This is simply for the greater good.

[saveasteading]

4 minutes ago, Nickfromwales said:

tantalised planks

My favourite joinery product.

 

To excite (planks) by exposing something desirable that remains or is made difficult or impossible to obtain.

 

I have just instructed spellcheck on here to add tanalise  to the dictionary and it seems to have worked.

 

I think you are right re the air resistance if the outlet is pointing at the fence, but it would be ok if the outlet was upwards.

 

The reason for the planks being on opposite sides is that this alters the frequency of the noise, so it dissipates, but allows most air through, including wind. 

Your version will prob do both to sufficient extent. It conceals the ugly box too.

 

 

 

[Nickfromwales]

28 minutes ago, saveasteading said:

My sketch is attached.....I am no draughtsman. Not looking for comments although they are welcome of course. This is simply for the greater good.

Thanks for this. A consideration for one new client so was going to be asking about this in due course. No time like the present lol. 
So, my question is around the risk from fire / flames going back down the air intake? Are there regs for this? Is it even a problem / consideration? 
If the air intake is this piddly flexi hose, how is it that this can be connected directly to the WBS and there not be a certain length of more robust flue-like pipe connected immediately?

All thoughts / wisdom welcome. For my client it will be a double-sided appliance, shared between two rooms, so assume a bottom connection vs rear entry. Better maybe? 

Edited March 21, 2022 by Nickfromwales

[saveasteading]

1 minute ago, Nickfromwales said:

risk from fire / flames going back down the air intake

It sounds like a possibility but I don't think so. The theory of stack ventilation should apply here, as well as 'hot air rises'.

 

To burn back down the intake, the flames would have to go down through the grate which seems unlikely (have you noticed that under a bonfire there can still be some unburnt material, protected by the ash?

 

Plus the wind across a flue causes upward movement of air, so in the summer this will act as a permanent air flow.

 

Yes, I get smoke and even some flame coming out of the door when ours is just lit, so that is working in reverse, but when burning well it all goes up.

 

And even if all that theory was wrong, and there was occasional backfiring,  it is an aluminium pipe, several metres long.....no harm will be done.

 

I showed a pvc drain-pipe at the wall because this can go in early and not get damaged. we don't have the possibility of going through the wall as it is 600 th granite. I haven't given any thought to doing it through a nice easy timber wall.

 

[Onoff]

10 minutes ago, Nickfromwales said:

so assume a bottom connection vs rear entry. Better maybe? 

Edited 6 minutes ago by Nickfromwales

 

🤐

[ProDave]

Our stove is ducted air intake.  IIRC it was an 80mm diameter inlet connector and I just bought 80mm flexible aluminium pipe, not the really flimsy one but quite solid.  That connects to my adaptor in the wall that leads down to under the ventilated suspended floor.

 

The pipe connecting to the stove must be non combustible.

 

I really can't see any risk of flames going down the intake.  The intake is well below the firebox underneath the ash pan.  I cannot imagine what sort of backdraught situation would send flames down there.  

 

If you touch the vent pipe when the stove is running it is cold, because it is drawing in cold outside air.

 

Take care when buying a stove that it takes both primary and secondary air from the ducted intake, not all do.

 

BC didn't seem bothered that the stove I fitted was different to what was on the building warrant, they just wanted to see the manual and check the "distance to combustible materials" stated in the manual had been met.

 

 

[saveasteading]

32 minutes ago, ProDave said:

secondary air from the ducted intake

That being the air that comes out of nozzles in the fire bricks and burns the fumes?

 

Are there any rules on that? I am thinking that if any air can get in other than through the duct, then that might become the primary source if the pressures allow.

[Nickfromwales]

48 minutes ago, ProDave said:

Take care when buying a stove that it takes both primary and secondary air from the ducted intake, not all do.

What are the definitions of primary and secondary?

[ProDave]

1 hour ago, Nickfromwales said:

What are the definitions of primary and secondary?

Primary is air in at the bottom of the firebox, for coal. Secondary is air in at the top of the firebox for wood.

 

Some stoves only take the bottom primary air from the duct and simply open vents on the door to take the top secondary air from the room.

[saveasteading]

My stoves have  sliding openings at the bottom front, into the ash pan. No fancy sliders or pivots, just air in at the hole in the front. This then comes up through the grille unless covered in ash, and round the back of the fire bricks and out of numerous holes into the fire box.

Works fine as long as the ash pan is not full.

Wood needs to sit on ash (or a solid bottom) but mine seems to work when air comes from under just as well.

I noticed that some modern fires don't have ash pans, yet some do.

[Gus Potter]

6 hours ago, saveasteading said:

My sketch is attached.....I am no draughtsman. Not looking for comments although they are welcome of course. This is simply for the greater good.

Good sketch.

 

Can you drop the duct so you get some insulation over the top of it to mitigate the cold bridge? In parts of Scotland it regularly gets down to minus 15 -18 deg C.

 

We have a 5.0kW stove with a bottom intake that can be ducted. I do have a duct from the solum space to hearth level and it pops up just under the intake but is not actually connected to it. When the stove is on you can really feel the air flow if you put your hand under the stove, but the cold air is drawn directly into the stove rather than over your feet / under the door. The rest of the room is reasonably sealed so when the stove is not on the room is ventilated.. it's not a passive house.

 

One day I may connect the duct to the stove intake and see what happens.

 

 

 

 

[Marvin]

6 hours ago, saveasteading said:

7 hours ago, Marvin said:

installed on the flat roof

Does it have acoustic bearings/pads? It could otherwise set up a hum through the joists.

Hi @saveasteading 

 

 

We have not had any issue with humming and the bed is below about 10 foot away.

 

As this was a retrofit on a renovation which we lived in for 4 years with a gas boiler after renovating, before installing the ASHP, I can safely say that the swap has made no difference on the noise front.