Sean W
@insan3gl0ss.bsky.social
It’s really not difficult to get 400%, just some bigger radiators / tighter UFH spacing to allow flow temperature reduction.
I’m averaging 410% on my Viessmann Vitocal in a 1930’s UK semi detached house.
If you’re not getting 340%+ it’s been designed/installed badly.
I’m averaging 410% on my Viessmann Vitocal in a 1930’s UK semi detached house.
If you’re not getting 340%+ it’s been designed/installed badly.
November 9, 2025 at 7:55 AM
It’s really not difficult to get 400%, just some bigger radiators / tighter UFH spacing to allow flow temperature reduction.
I’m averaging 410% on my Viessmann Vitocal in a 1930’s UK semi detached house.
If you’re not getting 340%+ it’s been designed/installed badly.
I’m averaging 410% on my Viessmann Vitocal in a 1930’s UK semi detached house.
If you’re not getting 340%+ it’s been designed/installed badly.
Doesn’t sound like it if 60c is working at present, maybe at worst a few rad changes perhaps going from single to double panel for example. Try 55c over winter and see how you get on. If that works then no changes *needed* and you can be running at the same cost of gas (assuming price cap rates)
July 25, 2025 at 3:14 PM
Doesn’t sound like it if 60c is working at present, maybe at worst a few rad changes perhaps going from single to double panel for example. Try 55c over winter and see how you get on. If that works then no changes *needed* and you can be running at the same cost of gas (assuming price cap rates)
Using free online software, I did my own heat loss survey and then could calculate the sizes of the radiators at a maximum of 40c flow temperature when it’s -3c outside. This is what I set my boiler to (actually a little lower). I then run a flat indoor temp 20c all day and 19c at night.
May 31, 2025 at 6:25 AM
Using free online software, I did my own heat loss survey and then could calculate the sizes of the radiators at a maximum of 40c flow temperature when it’s -3c outside. This is what I set my boiler to (actually a little lower). I then run a flat indoor temp 20c all day and 19c at night.
Here’s the maintenance checklist on the Viessmann Vitocal 15X-A, bar a couple of things like the refrigerant circuit (which if there was a problem would stop the HP working anyway) - nothing much to it.
March 21, 2025 at 8:03 AM
Here’s the maintenance checklist on the Viessmann Vitocal 15X-A, bar a couple of things like the refrigerant circuit (which if there was a problem would stop the HP working anyway) - nothing much to it.
Not only that, you can run your HP on ToU tariffs to get even further benefits. All I’m saying is don’t dismiss them.
March 20, 2025 at 9:48 PM
Not only that, you can run your HP on ToU tariffs to get even further benefits. All I’m saying is don’t dismiss them.
Whereas a decent HP install you can be down in the 5-6p kWh of heat which I cannot see a storage heater system delivering. Never mind the comfort benefits of continuous gentle heat.
heatpumpmonitor.org?mode=costs
heatpumpmonitor.org?mode=costs
March 20, 2025 at 9:44 PM
Whereas a decent HP install you can be down in the 5-6p kWh of heat which I cannot see a storage heater system delivering. Never mind the comfort benefits of continuous gentle heat.
heatpumpmonitor.org?mode=costs
heatpumpmonitor.org?mode=costs
The ratio between night E7 vs single rate is like 1.8 (currently ~13p vs ~23p/kWh). That just means you need a COP of 1.8 to beat storage heaters from a heat pump - which even the worst of the worst installs can do. Even if you’re banking on a ToU tariff like agile, the average low is still ~13p
March 20, 2025 at 9:40 PM
The ratio between night E7 vs single rate is like 1.8 (currently ~13p vs ~23p/kWh). That just means you need a COP of 1.8 to beat storage heaters from a heat pump - which even the worst of the worst installs can do. Even if you’re banking on a ToU tariff like agile, the average low is still ~13p
Fair, HPs are not easy to do as a distressed purchase! Just check your flow temperatures are as low as possible for extra efficiency, best not be throwing away gas where you don’t have to.
www.heatgeek.com/wp-content/u...
www.heatgeek.com/wp-content/u...
March 18, 2025 at 7:56 PM
Fair, HPs are not easy to do as a distressed purchase! Just check your flow temperatures are as low as possible for extra efficiency, best not be throwing away gas where you don’t have to.
www.heatgeek.com/wp-content/u...
www.heatgeek.com/wp-content/u...
Even the best most modern boilers are only as efficient as the flow temperature settings allow them to be. This is mine, it’s set at 38c flow, *almost* as efficient as can be. If the dial for the radiator symbol is above ~60 then the boiler doesn’t condense as is a good as the oldest boiler around.
March 17, 2025 at 5:59 PM
Even the best most modern boilers are only as efficient as the flow temperature settings allow them to be. This is mine, it’s set at 38c flow, *almost* as efficient as can be. If the dial for the radiator symbol is above ~60 then the boiler doesn’t condense as is a good as the oldest boiler around.
Did wonder why my Octopus Tracker had taken a tumble on gas..
February 26, 2025 at 11:11 AM
Did wonder why my Octopus Tracker had taken a tumble on gas..
This is the Viessmann Vitocal maintenance checklist. Apart from the refrigerant check - there’s nothing that couldn’t be done by the homeowner. I wouldn’t be doing the refrigerant check every year as you’ll know if there’s an issue when it throws an error.
January 30, 2025 at 11:23 AM
This is the Viessmann Vitocal maintenance checklist. Apart from the refrigerant check - there’s nothing that couldn’t be done by the homeowner. I wouldn’t be doing the refrigerant check every year as you’ll know if there’s an issue when it throws an error.
Hi Alexis, generally I thought the article was really quite good and reasonably well balanced, for articles in the media. However, I’d like to mention that you’ve mentioned something that’s not right - and that’s linking insulation to efficiency.
January 29, 2025 at 5:02 PM
Hi Alexis, generally I thought the article was really quite good and reasonably well balanced, for articles in the media. However, I’d like to mention that you’ve mentioned something that’s not right - and that’s linking insulation to efficiency.
Yeah I wouldn’t bother externally insulating with that. I would look to get the benefits from running a HP at the lowest flow temp practicable and get the the efficiency from there. Can be talking 20-25% reduction on energy bills if you’re at or lower 40c flow temp compared to gas just with big rads
January 13, 2025 at 10:04 AM
Yeah I wouldn’t bother externally insulating with that. I would look to get the benefits from running a HP at the lowest flow temp practicable and get the the efficiency from there. Can be talking 20-25% reduction on energy bills if you’re at or lower 40c flow temp compared to gas just with big rads
Well a good example is my office, this is the size of the rads here relative to the room but it’s designed to be 22c in this room, so quite warm!
January 13, 2025 at 9:09 AM
Well a good example is my office, this is the size of the rads here relative to the room but it’s designed to be 22c in this room, so quite warm!
See example table from a common high performance HP. Running at 55c is low to mid 3’s, whereas running at 35c is mid 4s. If you can beat ~3.5 the your running cheaper than gas (that’s the ratio of electricity to gas price, accounting for boiler efficiency of around 80%).
January 10, 2025 at 2:36 PM
See example table from a common high performance HP. Running at 55c is low to mid 3’s, whereas running at 35c is mid 4s. If you can beat ~3.5 the your running cheaper than gas (that’s the ratio of electricity to gas price, accounting for boiler efficiency of around 80%).
It’s also born out in the data in heatpumpmonitor. Only tariff that beats it is OVO Heat Pump Plus
December 4, 2024 at 10:20 AM
It’s also born out in the data in heatpumpmonitor. Only tariff that beats it is OVO Heat Pump Plus
The magic is getting an engineer that’s trained well (usually done the heatgeek courses). You’ll notice on heat pump monitor that highest performing systems are from those engineers who have done that type of training.
www.heatgeek.com/find-a-heat-...
www.heatgeek.com/find-a-heat-...
December 3, 2024 at 5:57 PM
The magic is getting an engineer that’s trained well (usually done the heatgeek courses). You’ll notice on heat pump monitor that highest performing systems are from those engineers who have done that type of training.
www.heatgeek.com/find-a-heat-...
www.heatgeek.com/find-a-heat-...
And it’s not that big at 8.13% for last quarter - that’s 3.38% better than base rate in a bank, and you’ve got to the effort of doing *all* the things National Grid have to do to earn that extra 3.38% over just sticking it in a bank.
November 30, 2024 at 10:47 AM
And it’s not that big at 8.13% for last quarter - that’s 3.38% better than base rate in a bank, and you’ve got to the effort of doing *all* the things National Grid have to do to earn that extra 3.38% over just sticking it in a bank.
You can actually see in heatpump monitor the difference in tariffs in p/heat delivered. Note they are much lower than the gas price cap.
November 26, 2024 at 10:51 AM
You can actually see in heatpump monitor the difference in tariffs in p/heat delivered. Note they are much lower than the gas price cap.
I’m the same in that not yet got a heat pump - but have prepped my house for one (upgraded all rads for a design flow temp of 40c at -3.1c OAT). Running my boiler at 38c and oh my god I’m still too hot at 21.2c. Target is 20c.
November 19, 2024 at 11:32 AM
I’m the same in that not yet got a heat pump - but have prepped my house for one (upgraded all rads for a design flow temp of 40c at -3.1c OAT). Running my boiler at 38c and oh my god I’m still too hot at 21.2c. Target is 20c.
I would suggest that the HP should be sized as close to the design temperatures as possible, if not fractionally undersized. But the caveat is you have cheap convector for the handful of days a year you need it. Could be to warm up the building quickly keep extra toasty on the 0.5% of days.
November 18, 2024 at 2:39 PM
I would suggest that the HP should be sized as close to the design temperatures as possible, if not fractionally undersized. But the caveat is you have cheap convector for the handful of days a year you need it. Could be to warm up the building quickly keep extra toasty on the 0.5% of days.
What electricity prices are you using - price cap I presume? Just that there is options for potential significant savings on more smart tariffs. See the difference when you change tariffs on heatpumpmonitor.org?mode=costs and then change the tariffs to see what effects it has. Could change the view?
November 18, 2024 at 10:50 AM
What electricity prices are you using - price cap I presume? Just that there is options for potential significant savings on more smart tariffs. See the difference when you change tariffs on heatpumpmonitor.org?mode=costs and then change the tariffs to see what effects it has. Could change the view?
You can see the effects with the reference tariffs. The idea is that you want to close the spark gap, and you’re not going to do that on the price cap. You need to do something else, so looking at Octopus Agile or OVO heat pump plus. They have their drawbacks elsewhere obviously, but worth checking.
November 12, 2024 at 8:57 AM
You can see the effects with the reference tariffs. The idea is that you want to close the spark gap, and you’re not going to do that on the price cap. You need to do something else, so looking at Octopus Agile or OVO heat pump plus. They have their drawbacks elsewhere obviously, but worth checking.
Have you checked out heatpumpmonitor.org and seen what effect tariffs have? Could improve your return on investment if you haven’t.
November 11, 2024 at 6:26 PM
Have you checked out heatpumpmonitor.org and seen what effect tariffs have? Could improve your return on investment if you haven’t.