ASHP in uninsulated home?

[PennineDave]

Hi,

A couple of years ago my partner and I bought an old stone house in the North Pennines. Since then we've been saving up and figuring out what to do with the place, with a general plan to eventually go round room by room and insulate internally. I've been battling with a mouse problem in the loft that needs resolving before I can replace the loft insulation they've ruined, and the suspended floor in part of the downstairs is rotten from an extension blocking the vents and a leaky drain. Basically, the house is very inefficient and we both work from home so it costs us a lot to heat.

 

But the immediate problem is our oil boiler is on its last legs. I'm wondering if it would it be a terrible idea to get an ASHP now, and then carry on with the works we have planned later? We'd like to be more eco friendly and it opens the door to using solar power for heating in the future, as well as not having to worry about getting oil delivered. But they're more expensive and I'm concerned that if we got one for our current heat load it wouldn't work very efficiently once we did everything else, as I understand they have to be sized correctly to work well.

 

Please can anyone offer any insight? Thanks.

[Redbeard]

Much as I like to advise getting the heat-loss down as low as possible before considering a HP it is not true that they won't work in a poorly-insulated property, but they may cost a fortune to run, or simply even not be big enough (most single-phase HPs max out at 16kW). Depends a lot on the size of your house. Depending on the current flow temp of your boiler (some old houses run at 60 - 70C) you may need to increase the size of some or all rads. There are high-temp HPs but I am not at all sure of the CoPs (Co-efficient of performance - kWh of heat out for each kWh of elec to run the HP) they offer. You are right also that an over-sized pump (as you improve the fabric performance) could be an issue, though others will know more than I do about HP modulation - effectively the ability to 'behave' like a smaller 'boiler' and not shorten its own life by short-cycling a lot. A buffer tank may be recommended too

 

I am not sure that

52 minutes ago, PennineDave said:

it opens the door to using solar power for heating in the future,

 

unless you either have a **huge** array of solar and batteries or need a lot of heat in the summer. By all means note that if you have a HP a sunny day may offer a little bit of help to it, but I would not be expecting much.

 

Lots of advice on here already re internal insulation and what is best for old stone buildings. Does your house have a high degree of exposure?

[Dillsue]

We're almost into May already and without any firm plans you probably want to get the oil boiler ship shape to see you through next winter. Then do your research and build a plan as to the work you want to do. Once you have a plan you'll be able to size your heat pump more accurately based on the draught proofing and insulation levels in the plan.

 

Remove the loft insulation and buy a box of 10 little nipper mouse traps. Once youve cleared the mice, seal up all the pentrations where cables/pipes come through the ceiling, fit rodent proof vents to the eaves and refit the insulation. You might want to use PIR over the tops of the walls to give decent insulation between rafters but leaving enough of an air gap to get airflow across the loft space.

 

Don't expect any solar PV to contribute much to running your heat pump as solar generation is at its lowest in the winter when heat demand is at its highest

[JohnMo]

1 hour ago, PennineDave said:

understand they have to be sized correctly to work well

Sort of right but somewhat oversold as heat pumps modulate power down reasonably well in most cases.

 

A house needs a given amount of heat and to a large degree the same kWh of heat is the same for any heat source.  The thing that cripples (makes them costly to run) heat pumps is flow temperature. 

 

So the ideal is a heat pump heating system designed to a max of a out 40 and no more than 45 degs. The lower the flow temp the less it costs to run.

[SteamyTea]

Welcome.

 

Two things have struck me about your problem.

You want to sort your loft insulation out.

You want PV.

 

Can those two be done together? I.e. strip roof, sort mouseholes and fit the insulation and PV.

 

You could then use the PV generation to heat the DHW (assuming you have a cylinder) and maybe use some to supplement the space heating (a fan heater costs a tenner).

 

As oil boilers are pretty basic bits of kit (a fuel pump, a fan and a heat exchanger), can you get it repaired enough to get you though the next year while you sort the house out, thermally.

There is a good chance that because if the Trump policies, oil prices will drop.

[Iceverge]

Sounds like a JCB renovation is needed. 

 

 

Failing that.... patch up the boiler. We can sometimes wish old things out of existence but they may decades left of annoying us left in them. 

 

Tackle the fabric of the building before going anywhere near a heat pump or solar. 

 

In this order. 

 

1. Bulk water, fix the gutters, point stonework and render, mend broken roof slates, and importantly make sure the local water table cannot get anywhere near floor level. This may involve digging and some French drains.

 

2. Install some mechanical ventilation. A couple of dMev fans like the greenwood cv2gip would be ace. 

 

3. Airtightness, stop all drafts. It can be achievable with persistence. 

 

4. Insulation, it needs to be continuous and sufficient. 

 

 

Only then should you go anywhere near your heating system. 

 

 

 

[Iceverge]

Have you considered building a garden room for WFH? 

 

Airtight with a dMVHR unit and good insulation and you'd be amazed at how comfortable it would be. I suspect so amazed you might do the sensible thing to the current house and put it out of its misery.

[ReedRichards]

16 hours ago, PennineDave said:

I've been battling with a mouse problem in the loft that needs resolving before I can replace the loft insulation they've ruined

 

Every autumn, field mice take up residence my loft to spend the winter; I have no idea how they manage to get in.  I trap and remove them but it's a constant battle for a few months.  They like to chew on the pipe insulation but have never touched the foil-covered type; I use Kingspan Kooltherm.  The downside to this is that it takes a long time to install, making it a DIY job rather than something you could afford to pay a tradesperson to do.

[JohnMo]

We had an infestation of rodents in 22. I ended up using bait stations, which have worked well. First year we got through about 8kg of poison.

[PennineDave]

Thanks everyone for the suggestions. We don't have the money right now to install solar and definitely not enough to demolish and rebuild! That's very interesting about the foil covered insulation ReedRichards, I might give that a go.

 

Currently leaning towards replacing with another oil boiler and carrying on with other improvements as time and funds allow.

[Nickfromwales]

4 minutes ago, PennineDave said:

Currently leaning towards replacing with another oil boiler and carrying on with other improvements as time and funds allow

Good idea, just know with every improvement you’ll then be using less and less oil per annum.

 

Solar would never contribute to heating so that’s put to bed, but solar PV is an absolute no brainer so pursue that asap. If you defo are going to do PV then avoid going to an oil combi, as you won’t be able to store excess PV as hot water (via the immersion).

 

Reducing draughts from the house will outshine thickening up any planned insulation, so spend smarter   

[Dillsue]

1 hour ago, PennineDave said:

Currently leaning towards replacing with another oil boiler and carrying on with other improvements as time and funds allow.

Save a search on ebay for your current model of oil boiler and you might surprise yourself with a good working spares boiler

[lookseehear]

5 hours ago, Dillsue said:

Save a search on ebay for your current model of oil boiler and you might surprise yourself with a good working spares boiler

We looked at putting in a 'lightly used' oil boiler (2 years old) because a friend was getting rid of theirs in favour of an ASHP. None of the installers we spoke to (three in total) would install a second hand boiler due to (in their words) risks that it might be defective or have been removed incorrectly/without care.

 

Our three quotes for a replacement oil boiler and a new unvented cylinder, as well as putting TRVs on 10 existing radiators was around £7k in total from all three installers, with the actual boiler and cylinder being around £2.5k of that (external Worcester Bosch model). Most of the cost was therefore in the installation and going second hand wouldn't have saved us all that much.

[sharpener]

15 hours ago, Dillsue said:

Save a search on ebay for your current model of oil boiler and you might surprise yourself with a good working spares boiler

 

IIRC there is a firm in NI on ebay which specialises in 2nd hand boilers. Shipment might be expensive.

 

When we installed the HP there was a fully operational oil boiler which I advertised as suitable for spares (including on here) but in the end there were no takers and it went for scrap.

 

However oil boilers are pretty robust and the spares for even 20+y/o models fairly generic and widely available. So unless there is some major failing like the main shell is rusted through they can be kept going more or less indefinitely.