Making your home cheaper to run this coming winter is likely to be on your radar and if so, chances are you’ve been thinking about replacing your boiler with a heat pump.
The first question to ask is whether an insulation upgrade alone, which you would need to do anyway before you change your heating system, would be more cost effective.
Secondly would replacing your existing boiler with a new condensing oil or gas fired model be more cost effective than a heat pump over the lifetime of the appliance?
Grant
Administered by the ROI Sustainable Energy Authority of Ireland (SEAI), the Better Homes scheme offers homes that were built before 2011 a grant of €3,500 to install air to water, ground to water, exhaust air to water and water to water heat pumps and €600 for air to air heat pumps (which involve far less capital expense).
The grant also contributes €200 towards the cost of an energy assessment, a pre-requisite for funding, carried out by an SEAI registered technical advisor, who will advise on measures to reduce the heat loss of the dwelling to 2W/K/sqm – also a pre-requisite.
Typically this will involve fabric insulation and airtightness measures. Indeed the scheme documentation warns that “uninsulated homes built more than 30 years ago may require substantial and costly upgrades to qualify” for the grant.
Before its much publicised suspension, the Northern Ireland Domestic Renewable Heat Incentive provided an upfront payment of £1,700 for an air source heat pump and £3,500 for ground source, with ongoing payments of 3.84p/kWh and 9.00p/kWh respectively. It remains to be seen whether the scheme will be revived or replaced with anything similar.
Comparison
Let’s take a base-case 150 sqm dwelling, a 1970s detached bungalow such as is commonly found in rural Ireland and which presumably is one of the key dwelling types targeted by the grant-aiding programme.
I used energy rating software to find out how much energy a house like that would consume; to calculate annual heating costs I multiplied the space heating load by the current fuel unit costs for electricity and oil. The current fuel prices are 16c/kWh for electricity and 7.5c/kWh for oil.
I then applied carbon dioxide emission factors for grid electricity (0.483 kgCO2/ kWh) and heating oil (0.264 kgCO2/ kWh) to give a total annual CO2 emission profile. All of the data comes from SEAI publications.
The heat pump scenario required extensive fabric enhancement, this is to make sure the low temperature system works as efficiently as possible. Comfort temperatures were taken into account in the energy software.
We are replacing the windows with low-e coated, argon-filled triple glazing; I assumed the original 1970s windows had been replaced with double glazing around the 1990s and had a U-value about 3.3W/ sqmK, though new double glazing tends to be around the 2.8W/sqmK mark and the very best available currently are around 1.4W/sqmK. For reference, triple glazing offers overall U-values of less than 1W/sqmK and some even as low as 0.7W/sqmK.
The fabric insulation measures for the heat pump and enhanced oil option
assumed fillable wall cavities. If that were not the case and external or internal wall insulation were required, the economics (and level of disruption) would be considerable. The SEAI Deep Retrofit pilot programme reported measures can cost up to €60,000 per dwelling – even after 35 per cent funding.
Verdict
By all means install a heat pump in your new, very low heat loss house; you will need a certain level of renewable energy technologies anyway in order to comply with the Building Regulations in ROI (Part L) although no such requirement exists regarding Part F1 in NI as of yet. If you are going to superinsulate a new build you might consider going so low energy as to not need a central heating system (boiler or heat pump), although you will still need a device to generate hot water.
But retrofitting heat pumps into existing dwellings, with all the required thermal improvements, is currently not as cost effective as replacing your boiler with an upgraded model.