Going green on natural gas heating. The economics don’t stack up.

Since the start of the pandemic my partner and I have been working from home 4-5 days per week.  We are fortunate enough to have a study that is large enough for two desks and, not being in a city centre, just about adequate broadband for us both to do simultaneous online meetings.

Since it’s started getting colder we’ve had the luxury of putting our imitation-coal gas fire on to warm the room. That saves heating the entire four bed house all day, and boy does it make the study toasty quickly. And so it should, as, according to the manufacturer’s data it’s putting out 3.8kw of heat per hour when on the max setting. Sadly, the manufacturers say it consumes gas that could produce 6.2kw of heat per hour on maximum setting. By their figures that makes it 61% efficient which is pretty poor in my book.

Early in lockdown we had the whole gas system checked as part of a routine service. The engineer reported this fire is only 49% efficient. Thank God the Glow-worm boiler is 98% his printout reads (is that really true?)

As someone who really tries to do my bit for the environment, I was pretty disappointed to hear that. The figures for modern glass fronted fires reach almost 90% so I considered swapping the fire over.

This blog is to try to see whether changing it to a new modern fire is economical or not.

I’ve considered if I’m using the fire in the study on full setting for an hour and then on the lowest setting for 5 hours on five days a week for say 20 weeks a year – November through to April that the costs would be akin to those in the table below. I’m paying 2.56p per kWh including VAT though OutfoxtheMarket.com.

Setting kWh consumptionCost in pence kWh inc VATHours per dayDays per weekWeeks per yearVolumeCost in pence
Total in £41.42

This seems a staggeringly low figure to keep us both comfortable all winter. Especially given the cost of replacing this fire for a new more efficient one would be around a grand.

I looked at the costs of the house’s gas consumption over all the time I’ve lived in it. The data shows we’re using about 2.82m3 per day, on average. To get the kWh rate from that you have to multiply this volume by a fiddle factor, 1.022640, and by the calorific value of the gas, usually around 39 and then divide all that by 3.6 to get a kWh. I calculate that to be 32kWh, at 2.56p for 365 days comes to a total of £300 per year for almost 12000kWh.

My consumption in summer months is negligible. I have solar panels and an iBoost gadget that switches on the immersion heater whenever the panels are producing more electricity than the rest of the house is using. In the summer the iBoost is generally working before I’ve got up and had my morning shower and it carries on all day providing free hot water all summer. The data proves it!

Clearly most of that annual use is heating water in the winter and heating the rest of our house whenever the temperature dips too much and only a small proportion is the study fire. If I changed the current model to a 90% efficient one I’ll be saving less than 50% of its current costs and so if that’s around £20 benefit a year it’s going to take 50 years to get our money back! Given I’m over the half century I think this one area I can’t be green unless anyone tells me my maths or the cost of installing a more efficient model are wrong. I know I haven’t included the potential resale value of the old one, but let’s be realistic, if it goes for £100 that doesn’t make a big enough difference for the economics to stack up of taking it out.

I almost booked a survey for a new one today, and then, I thought, I’ll just check the maths. Please tell me if I’ve got it all wrong.

Stay warm and stay safe.