Air to Water v. Natural Gas

cb102

Hi
I am about to embark on a house extension and a refurb and re-model.  It’s a big job. I intend on having the house fully insulated to regulation standards, all external walls, the concrete slap, roof and triple glaze.  I am not intending installing a Heat Recovery system.
(The house currently with poor insulation has natural gas.)
Initially I was decided on an Air to Water solution with underfloor heating on the ground floor.
I am now questioning my decision. If the house is fully insulated, the amount of heat required to heat the house should be minimum right? So with a highly efficient gas boiler, my heating bills should be low anyway?
I am having trouble justifying the initial financial expenditure of Air to Water solution and replacing main unit in 15-20 years @ €10k, for example.  The decision is not as clear as Oil v Air to Water.
My heart tells me Air to Water (for renewable reasons) but my head tells me Natural Gas (for financial reasons).I am having trouble justifying the initial financial expenditure of Air to Water solution and replacing main unit in 15-20 years @ €10k, for example.
Thanks in advance for your feedback

Chris

KCross

If you have a fully refurbished house with decent insulation and new windows how are you planning on ventilating the house without Heat Recovery?

Opening windows for that will blow away any idea of your heating bill being "minimum" and thats apart from the humidity and mould issues that you could cause.

I think you should reconsider that decision.

bunderoon

cb102 wrote: »

Hi
I am about to embark on a house extension and a refurb and re-model.  It’s a big job. I intend on having the house fully insulated to regulation standards, all external walls, the concrete slap, roof and triple glaze.  I am not intending installing a Heat Recovery system.
(The house currently with poor insulation has natural gas.)
Initially I was decided on an Air to Water solution with underfloor heating on the ground floor.
I am now questioning my decision. If the house is fully insulated, the amount of heat required to heat the house should be minimum right? So with a highly efficient gas boiler, my heating bills should be low anyway?
I am having trouble justifying the initial financial expenditure of Air to Water solution and replacing main unit in 15-20 years @ €10k, for example.  The decision is not as clear as Oil v Air to Water.
My heart tells me Air to Water (for renewable reasons) but my head tells me Natural Gas (for financial reasons).I am having trouble justifying the initial financial expenditure of Air to Water solution and replacing main unit in 15-20 years @ €10k, for example.
Thanks in advance for your feedback

Chris

If you are getting a mortgage, are you factoring in the interest aswell?
20 years at 10K at 4ish % would be ~5K

so #15k is a rough cost of this system. What would the system save you over 20 years vrs a decent house with insulation, condensor boiler / Stove etc?

gooner99

I could be wrong, but I'd say mains natural gas is still the cheapest way to heat your house when you consider pay back time for the heat pump. Your right that your energy demand should be reduced with the work you are doing. You could invest the money saved on a heat pump in a mhrv or demand control ventilation.

murphaph

In that situation as you already have a gas connection I would go for high insulation and airtightness levels and (probably) demand controlled ventilation and a new efficient boiler. If everything is done properly the heat demand will fall considerably so you are doing your bit for the environment even without a heat pump! (which I have, so nothing against heat pumps).

IMO you're mad if you don't install either DCV or MHRV in a complete refurbishment. The air quality in a house with mechanical ventilation is far superior and you completely sidestep mould issues that are much more prevalent in highly airtight houses. When I see my poor neighbours in their brand new house opening the bathroom window wide at 7am to air the place with -10°C air I feel sorry for them.

Your boiler will also need replacing and at that point you can take another look at heat pumps but just make sure you lay out your UFH to be low temp friendly (narrower spacing of pipework than normal) so it doesn't prevent you using a heat pump later but be aware if you want to use rads upstairs it will always be sub optimal compared to UFH when run with a low temp heat source. Rads with a high temp source like a boiler will be fine, but with a low temp source will have to be massive and you'll have rust entering the system from the rads no matter what.

I considered rads for our basement but in the end discounted them and installed UFH there too (as in ground and first floors).

Conor20

In case it's useful, in another thread, I did a rough comparison of the costs of each system based on our own yearly heating energy consumption and the energy costs of each fuel type (electricity, gas, oil) from the SEAI, and came to the conclusion that a Heat Pump was the best option over a 15 year comparison period.

Conor20 wrote: »

Sure. I'm currently in research mode looking into the next step, and I will do this as part of that research. For the next investment (actually reinvestment, of savings from previous investments, particularly the electric car), I'm weighing up Battery Storage or a Heat Pump. Each have their merits. Battery storage provides a way to store excess Solar PV in summer, and to store cheap night rate electricity (€0.05 / kWh) in winter to remove daytime electricity costs (~€0.16 / kWh) - like PV, prices are falling rapidly, though it is still probably on the expensive side. A heat pump would allow us to heat the house fully with electricity, meaning we can generate it ourselves at a fixed price per kWh no matter what gas / oil markets do, remove our gas connection and it's costs completely, and obviously remove our gas bills.

Loyatemu, your question got me thinking about how to calculate this for everyone's different scenario rather than just one. Your figures look about right. Just doing some maths on the spot, converting the M^3 rate for gas into €/kWh, looking up the standard gas, electricity and oil costs from the SEAI here, and using my own house's heating load for 2016, here are some (very!) back of the envelope cost comparisons:

For the year of 2016, our house required 19,898kWh of heating. The various costs for this would be:

• Gas: 19,898 kWh * €0.0652 = €1,297.35
• Oil: 19,898 kWh * €0.0710 = €1,412.76
• Heat Pump (with 300% efficiency, with night rate electricity @ €0.05 / kWh): 19,898 kWh / 300% efficiency = 6,632.6667 kWh * €0.05 = €331.63
• Heat Pump (with 300% efficiency, half with excess PV @ €0.00 / kWh and half with night rate electricity @ €0.05 / kWh): ( (19,898 / 300% efficiency = 6,632.6667 / 2 = 3,316.3334 ) * €0.00 = €0.00) + ( (19,898 / 300% efficiency = 6,632.6667 / 2 = 3,316.3334 ) 3,316.3334 * €0.05 = €165.82) = €165.82 (the assumption in here around the split between excess PV and night rate here is tricky - most excess PV will be in summer when there is little heating requirement, so this figure will fall somewhere between €165.82 and €331.63, so let's take the average €165.82 + €331.63 = €497.45 / 2 = €248.73 ).

Assuming installation costs of: Gas (€2000), Oil (€3500), Heat Pump (€4000) and Heat Pump plus PV (€7000), coupled with their yearly running costs above for 15 years gives me this chart:


Total 15 year costs including installation come to:

• Gas Central Heating: €21,460.25
• Oil Central Heating: €24,691.40
• Heat Pump, Night Rate electricity: €8,974.45
• Heat Pump with PV: €10,730.95

The installation costs are rough estimates - I haven't installed these before so I'm not sure. But you could re-do the chart above yourself based on your own installation costs and heating requirements to figure out what is cheapest for you over the 15 years.

Oil and gas prices taken from here. If the Heat Pump is 300% efficient, it takes 19,898 kWh of heat / 3 = 6,632 kWh of electricity to pump in 19,898kWh of heat energy into the house.

gooner99

Would you buy a good heat pump for 4k?

Calahonda52

Night rate is only 9 hrs.
You might like to do location specific degree days cals for the heat pump as you may not get the hot water hot enough to cater for the legionella risks that are mitigated by heating the water above 60 or 65 degrees C