chrisgreen

Will ASHP or air-to-air be better for a 1930s detached, or storage heaters?

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Hello everyone! I'm new to the forum but have been reading it and it's great. 

 

We've recently moved into a 1930s detached brick cavity house (off the gas network, no current central heating). We're in Cumbria so it gets chilly!

 

We've been grappling with how to heat the house. It has no central heating, no ufh, no rads, just a log burner in lounge. The previous owners used an assortment of plug in and kerosene heaters. We've put in a (solar friendly) 250l unvented HW tank with immersion.

 

We want to work out which would be best: ASHP with low heat heaters (as there's no UFH), or Air-to-Air system (seem less popular than ASHP...why? Not as good?), or storage heaters, and how best to heat HW (solar thermal seems long pay back times though might be putting in with current RHI scheme?).

 

Energy prices are of course a big concern!! 

(We've discounted oil due to environmental issues).

 

The house: has 3 beds and family bathroom upstairs, and lounge, hall, dining room, utility all on suspended wooden floors which we took up, insulated between joists, then boarded before putting down limestone tiles. Builder warned us against cavity insulation for existing brick walls due to cavity bridging issue. (But not sure we could get ASHP RHI payments without it?!).

 

We've added on a 30m2 kitchen extension to ground floor side of house earlier this year - The new extension is a vaulted ceiling 25m2 kitchen extension off the existing dining room to the side of the house. It has insulated concrete floor plus insulated block walls.

 

We didn't futureproof with an UFH wet system (oh dear!) as we thought ASHP + low heat wall rads were a non-starter and would not manage to heat an older leaky house even with our added insulation measures, so we thought the only option was storage heaters with potentially solar thermal for HW. We're revisiting our decision due to the crazy current cost of electricity. 

 

We discounted solar PV at present as is expensive to put in and doesn't seem to give us enough energy when we need it.

 

Main house has double glazed windows put in 6 yrs ago, and new bifolds and double glazed windows in the extension put in earlier this year. We've added lots of loft insulation and added internal wall insulation to the rooms on the east wall of the house (lounge and 2x beds).

 

We aren't trade or DIYers as is probably clear with how I've described things! 

 

I've tried researching myself, but hard to make sense of the jargon. Also the sellers of heat lumps seem so keen to sell that we don't know if it's actually right for us or not! We had a ground source person come and quote but it was v expensive as we'd need bore holes as not enough space for horizontal array...this expense seemed risky given we weren't sure if a low heat systems would work in our older house! 

 

Any advice would a GREATLY appreciated! Feel like we're going round and round and definitely feeling our lack of technical know how! 

 

 

 

 

 

 

 

 

Edited by chrisgreen
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19 minutes ago, chrisgreen said:

Air-to-Air system (seem less popular than ASHP...why?

 I too am interested in this if anyone has more info.

 

Solar thermal is dead from what i understand. 

 

21 minutes ago, chrisgreen said:

Builder warned us against cavity insulation for existing brick walls due to cavity bridging issue.

 Do you have any more information on their logic here? Did they mention whether they were thinking about mineral wool, eps beads or closed cell foam? How wide is your cavity?

 

23 minutes ago, chrisgreen said:

RHI payments

 

think of this as a nice benefit if it works.your priority is a comfortable house.

 

25 minutes ago, chrisgreen said:

ASHP + low heat wall rads were a non-starter 

 

They might well be the case. Can you quantify your heat load now?  On a very cold day how much energy do you use per hr to keep warm?

 

Before you go throwing thousands and thousands at the heat lump (lol) suppliers you need to know what your house heating profile is as one of our other members found out recently they’ll happily sell you a pig in a poke. 

 

 

 

 

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Having previously lived in a 1930-s house I know they leak heat like it is going out of fashion.  Ours was 9" solid walls, if you really have a cavity that is an improvement.

 

Storage heaters were abysmal in ours, it was what was there when we moved in, and in the depths of winter the living room would not keep anything like a comfortable temperature with the storage heaters on full.

 

We fitted LPG gas central heating and the cost to run it (talking 20 years ago) was high, I would shudder to think what it is now.

 

In all honesty I would probably fit oil fired central heating to that.  But if you cant stomach that then I suspect you are going to want a pretty big ASHP and you are going to still be shocked at the running cost.

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30 minutes ago, Iceverge said:

Air-to-Air system (seem less popular than ASHP...why?

Tends to look industrial, can be noisy, can be draughty.

This is what goes in to commercial properties. Generally the air comes from units in the suspended ceiling but can be from louvres more discretely positioned. The heat has to be moved from the source to the outlet though so is still intrusive in a retrofit.

There are options where air is heated at a central point and ducted to outlets, then drawn back to 'base' for recirculation. This is much quieter but the ducts are big. I would consider this in  a new big house, as I know it works well in offices. 

 

Does this work in an existing house? Will depend on a lot of variables.

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Considered calor/equiv gas? 

 

With a big tank & careful buying it could be an option. 

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Silly question time:

 

Do I assume correctly that the ASHP air to air will not produce a way to heat your hot water?

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I think the problem with A2AHPs is they look a bit strange in the inside.

Your house layout is also important, they basically go though a wall.

It is the problem I am having in trying to decide between a wet system and an air system.

A wet system will use a lot of wall area for the radiators.

There is no reason you cannot have a combination of both.

 

As @ProDave said, old houses leak heat. My old Victorian terrace lost the lot in the 2 minutes it took to walk up the stairs.

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8 minutes ago, SteamyTea said:

There is no reason you cannot have a combination of both.

We are working with the Air to Water ASHP through the rads and installing coils in the existing MVHR to compensate for not enlarging the radiators.

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7 minutes ago, Marvin said:

We are working with the Air to Water ASHP through the rads and installing coils in the existing MVHR to compensate for not enlarging the radiators.

I have been wondering if I should get a small A2AHP, fit the internal unit in the loft, then pipe to the rooms.

I only need a couple of kW of heating. 

Then I thought I could incorporate some MVHR into it.

Being an 80s house, large, square or rectangular, louvred air vents would not look out if place.

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2 hours ago, Iceverge said:

 

 Do you have any more information on their logic here? Did they mention whether they were thinking about mineral wool, eps beads or closed cell foam? How wide is your cavity?

.....

They might well be the case. Can you quantify your heat load now?  On a very cold day how much energy do you use per hr to keep warm?

 

 

Will check with our builder on his logic and get back to you!

 

Heat load: as we only have a log burner, I don't have any energy/hr info I'm afraid...

 

I understand from another thread that the thing to do is calculate our heat loss per room to them workout how many kWh we need to heat each room? 

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2 hours ago, ProDave said:

 

In all honesty I would probably fit oil fired central heating to that.  But if you cant stomach that then I suspect you are going to want a pretty big ASHP and you are going to still be shocked at the running cost.

 

Thanks ProDave. If we have larger low heat rads in the house then does that mean we can run the ASHP at low temp (35degrees?) and would this mean higher COP and lower ASHP running cost?

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6 minutes ago, chrisgreen said:

 

Thanks ProDave. If we have larger low heat rads in the house then does that mean we can run the ASHP at low temp (35degrees?) and would this mean higher COP and lower ASHP running cost?

Yes. 

 

The nearer the output temp to the outside air temprature the more efficient 

Edited by Marvin
Clarification

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1 minute ago, chrisgreen said:

 

Thanks ProDave. If we have larger low heat rads in the house then does that mean we can run the ASHP at low temp (35degrees?) and would this mean higher COP and lower ASHP running cost?

I really doubt you will get the temperature down that low, even UFH in a house that needs a lot of heat might need more than that.  Probably more like 50 degrees is considered a low radiator temperature.

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59 minutes ago, SteamyTea said:

I have been wondering if I should get a small A2AHP, fit the internal unit in the loft, then pipe to the rooms.

I only need a couple of kW of heating. 

Then I thought I could incorporate some MVHR into it.

Being an 80s house, large, square or rectangular, louvred air vents would not look out if place.

 

Wondering the same...

Could we have two systems - an A2A in the loft, and a A2W for downstairs...

 

Or storage heaters upstairs and A2W downstairs given a good chunk of the downstairs is new build/better insulated...

 

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6 minutes ago, chrisgreen said:

 

Wondering the same...

Could we have two systems - an A2A in the loft, and a A2W for downstairs...

 

Or storage heaters upstairs and A2W downstairs given a good chunk of the downstairs is new build/better insulated...

 

My brother says it's not if but how much.

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13 minutes ago, chrisgreen said:

storage heaters upstairs and A2W downstairs given a good chunk of the downstairs is new build/better insulated

Better off with the more expensive to run storage heaters downstairs.

You really need to do a room by room heat loss calculation otherwise it is all guesswork.

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Best do some heat loss calculations now you have improved the building to get a better understanding of the energy requirement to heat your home.

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don't rush into this.

 

heat pumps are expensive to install and expensive to run, more so on older buildings.

 

You may be better off financially and heat wise with economy7 night stores. Heat pump install at circa 10-15k will pay for a lot of electric before you see any payback. 

 

Not to mention without thourghly insulating and having massive radiators (treble the size of normal ones) you will be cold.

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1 hour ago, chrisgreen said:

 

Heat load: as we only have a log burner, I don't have any energy/hr info I'm afraid...

On a calm night. Close all the exterior windows and doors. Open all internal doors wide open. Turn off any other heating and log burner. 

 

Put a cheap 2kW electric radiator in the centre of the house. Allow the temperature to stabilise overnight.  Take an average internal temperature and an external temperature in the morning. 

 

From here you will have a pretty good idea of your heat loss.  If your external temp is 10 and internal 15. You will use 2000W/5deg or 400W/degree.  Assuming worst case of -5 degrees 25*400w= 10000W or 10 kW 

 

Add a little safety factor for a windy night, say 25% and you should be able to get by with a 12.5kW heat pump minimum (excluding DHW)  Remember oversizing heatpumps is generally a good thing as they will return a higher COP and defrost less often.  

 

 

 

 

 

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2 hours ago, chrisgreen said:

 

Thanks ProDave. If we have larger low heat rads in the house then does that mean we can run the ASHP at low temp (35degrees?) and would this mean higher COP and lower ASHP running cost?

 

Possible, yes. Our last house we had low temp radiator system running from a heat pump. There's nothing special about the radiators, other than they have to be a lot bigger compared to your usual gas or oil system. In our case they were roughly 4 times the size (surface area).  Pipework feeding also needed to be 15 or 22 mm (sorry, can't remember which) - microbore simply would not work.

 

Our system ran at a flow temp of 33C at 0C ambient, but that was a new, very well insulated house.

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Regarding radiator sizing. It is the same calculation as working out heat loss through a window, door, wall, roof or even a DHW cylinder.

It is the product of the power flow, surface area and temperature differences.

There is a slight modification for convection currents, but they can generally be ignored in low running temperature systems.

 

As a general rule, as something gets hotter, compared to the surrounding temperature, it needs a disproportionate greater amount of power (energy divided by time) to maintain that temperature.

I have never done the calculations on a low temperature systems, but it might be useful.

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On 17/10/2021 at 11:44, SteamyTea said:

I think the problem with A2AHPs is they look a bit strange in the inside.

Your house layout is also important, they basically go though a wall.

It is the problem I am having in trying to decide between a wet system and an air system.

A wet system will use a lot of wall area for the radiators.

There is no reason you cannot have a combination of both.

 

As @ProDave said, old houses leak heat. My old Victorian terrace lost the lot in the 2 minutes it took to walk up the stairs.

 

We had a lot of hot air ducted heating systems installed in the 1960s/1970s that came out on skirting or floor vents.

 

As children we loves sitting in front of the vents.

 

Making a comeback?

 

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On 17/10/2021 at 13:02, chrisgreen said:

 

Thanks ProDave. If we have larger low heat rads in the house then does that mean we can run the ASHP at low temp (35degrees?) and would this mean higher COP and lower ASHP running cost?

 

One option to look at is simply to upgrade heat emission is to replace your existing rads with double ones, which will fit the same space.

 

Though when I upgrade an old house I tend to switch the rads from under window - as windows no longer leak and are warmer - onto inside walls, which are closer together and keep the heat in the house.

 

F

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I have had 4 Mitsubishi LN A2AHP's installed roughly 2 months ago. they total 15.5kW output (2x5kW Kitchen and conservatory, 3.5kW in lounge and 2.5kW in main bedroom - we are in a bungalow 120sq/m).

 

My heat load for the property is 12,500kw and water 2000kw. Until these were fitted I was running a pellet boiler for the past 7 years typical pellet cost was £1200pa

 

I have been logging my daily running costs and room temps since the A2AHP's have been installed and comparing costs to pellets. From what I can see so far (only end Aug/Sep and uptown today) the running cost is averaging 79p a day (elec cost is19.3p/unit btw)

 

Observations

Temp set at 24c on all units (wife has illness needs high temp) all rooms in property achieve 23.5c or above. The airflow via the 4 units flows into other bedrooms, bathroom etc. I honestly thought we would need another small unit to balance the heat in all rooms but so far this clearly is not needed.

 

running costs are very low in 65 days saved over £75 over pellets.

 

Heat is far more comfortable than using boiler/rads stays very even

 

No draughts or noise as always on they just tick over. Also the Mitsubishi LN units have a built in thermal camera that is used to detect people and can direct the airflow so that it doesn't blow on you (or you can set it to blow directly on you if you like) this also works as you move around the room really good feature.

 

Down sides

4 units outside - you need the space for them or use a multi split unit ( I was advised against this as I had space - with one unit all internal units are on either heat or cool, with separate units you can mix and match eg 1 heating with 3 cooling etc etc. Also if one outdoor unit fails unlikely but possible the other 3 can continue to heat/cool) Cost wise only a few hundred quid between a multi split and 4 separate units.

 

Water heating not possible with A2AHP - we have solar thermal and 10KW of PV so water heating is covered for us but something to consider if going this way.

 

Below is a snapshot of my summary data I plan to continue to monitor for the full 12months and extrapolate the data to be able to predict my running costs based on outside temp eg 6 degree = £1.10 day, 12 degrees = 60p/day etc 

 

Feel free to ask any questions I will do my best to answer them.

 

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