Is Thermal Renovation Worthwhile?

(Amended slightly in early April 2016: we had some work done)

We bought a house, about 7km south-west of Tomar. It has fabulous views. Tomar has a lovely micro-climate - its warmer than immediate areas to all sides.

The original plans and permission date from 1990 and do not show any insulation at all.

We haven't decide how invasive we will be with the building, so I just investigated trying to make it a little more comfortable, and ideally cheaper to live in over Winter.

The building had:

• a small wall mounted water cylinder (read: it isn't very big)
• an ancient boiler that can I believe can burn wood, but has an oil burner adapter on the front
• radiators in most rooms (a couple are missing). They seem undersized. (Update: we replaced some during boiler replacement, see below, but they are still modest)
• a recuperador in the large public room, with soot marks next to an air vent on the side of the chimney

The old boiler was not automated at all - you manually turn on the pumps for circulation to the AQS cylinder and/or the central heating circulator.

The current price of oil does not really justify a replacement, but the lack of automation and general age of the equipment does, in my view - particularly for AQS, which we will use more in the short term.

So - I have modelled the house simplistically on an Excel spreadsheet. It has no macros and works fine in Open Office 4.1.1. I used Open Office to save an HTML snapshot.

I suspect I have been a little bit kind in my estimation of the cost of adding ETICS (EWI). It is probably not feasible to do it without messing with the shutters, window stones, and roof details, which suggests that the whole package of works is necessary. We might be able do the roof and windows without doing the walls, however.

The result of adding ETICS largely correlates with the optimisation discussed previously, in that we have annual savings of about €200 from adding it (the difference between scenarios C and B), against a cost of €13000. It actually seems a rather poor return, financially. But it may make the house nicer to live in.

If we consider the overall 'big package' - an annual fuel savings of about €750 against a spend of €33000, then the situation is perhaps not as bad as all that:

• the building should increase in value, although probably not by the capital expenditure. Arguably the replacement windows would do most for this, since the existing ones are clearly not state of the art and are draughty.
• the building should be less prone to overheating in summer through direct insolation on the roof, which is exposed to the living room downstairs and the upstairs bedrooms
• the building will be more comfortable (and more of it usable) from reduction of drafts and cold areas near glazing
• we would spend a lot less time feeding pellets into the boiler's hopper, or waiting for pallets of pellets to be delivered.

Still - justifying this requires a leap of faith regarding the effective capital value increase, and a degree of confidence in being able to keep to what may be considered a 'best case' budget. If it slips to a €500 savings against a €40000 then the rate of return is very poor and you have to justify a lot of it from added value for resale. Conditions in Portugal do not seem to justify that - it is still a buyers' market.

The actual cost of a pellet boiler does not seem to vary enough between 10kW or so and 20kW or so to make a huge difference, although it is worth bearing in mind. That does not necessarily hold for conversion to an ASHP system where there seems to be quite a direct correlation between capacity and cost for the compressor units. Unfortunately with a house of this size and age it is practical to consider 35kW or more for space heating or abandon it for Winter - and boilers of that capacity are much cheaper for oil (or diesel - local heating oil is more closely related to what you put in a car than we are used to in UK). Also - upgrading the electrical supply to the point that it can sustain that output even with a COP of 3 is not trivial, and the ASHP units are expensive, and I suspect the plumbing could not deliver enough flow for a low temperature supply even if the radiators were all changed to (expensive) fan-coil units.

The elephant in the room, however, is that we are not resident full-time over winter. If we offer the house on AirBnB or similar - then it still won't be let over much of the winter (if at all). And we can't realistically do that without replacing the tired bathrooms and the kitchen.

I guess the plan will be to:

• sort out a more convenient AQS system (done: I replaced the oil boiler with a Domusa model that is effectively a combi - the cylinder is retained as a backup with immersion heater and the coil is currently disconnected)
• make sure that we have some sort of solution for heating in winter and swing seasons (and after moving in, I can confirm that attempts to use electric heaters as a short-term solution when you have a 10amp 3-phase supply do not work)
• see how bad the overheating is in summer
• then decide what is worthwhile, given scenarios for architectural remodelling

The mechanics of thinking about these things has left me a little disheartened.

I have a recurring bad feeling about renovation as a way to save money through lower running costs. The capital costs are typically high - many case studies that show modest costs seem to have owners who have done rather large amounts of labour - or have used volunteer labour - or are in fact in the building trade. You will see 'we saved £1000 per annum on heating bills' more often than you will see an honest (or even approximate) assessment of the actual project cost including relocation and temporary accommodation - but they are two sides of the same coin unless you have unlimited funds and a desire to Do The Right Thing For Posterity.

It does seem that it is justifiable to make expenditure on the insulation and renewables iff you are making major changes already, and it is a case of choosing a different level of insulation, or a different standard of glazing unit, or a different type of heat source. Its hard to justify on a financial basis in other cases with the possible exception of direct replacement of a boiler with one that uses a cheaper fuel source. Even then - you have to be careful: wood burners are labour and space intensive and so are pellet burners: a 30kW boiler is not hard to buy, but it gets through cellulose mass quite quickly and you need to purchase, store (and dry, for green wood), load, and clean the system. It is emphatically not like having a condensing boiler on piped natural gas in the UK - even if the raw cost per kWHr is comparable.