Octopus heat pump

Temperatures in room columns are minimum radiator temperatures to meet Octopus heat losses (my heat losses in parentheses).

Temperatures in the flow column are minimum flow temperatures to meet Octopus heat losses (my heat losses in parentheses).

PlanP is like planN, but the original lounge and dining room radiators are used as the extras in the lounge and back room.

Monica 4b (planI) is like Monica 5c (planM), but the original lounge and dining room radiators are used as the extras in the lounge and back room, and slightly smaller radiators are used in the bedrooms and bathroom.

Plan	Lounge extra	Dining	Back room extra	Front bedroom	Back bedroom	Bathroom	Cost £	Flow °C	Daikin SCOP
Monica 1 planC	-	T21 600x600 833W	-	T11 400x700 460W	T11 400x700 460W	T11 600x400 410W	-	74	-
Monica 2 planL	-	K2 700x800 1568W	-	K2 450x1000 1371W	K2 450x800 1096W	K2 600x800 1385W	410	64	-
	51°C (53°C)	K2 700x800 1568W 51°C (51°C) £129	60°C (52°C)	K2 450x1000 1371W 47°C (45°C) £100	K2 450x800 1096W 45°C (44°C) £87	K2 600x600 1039W 45°C (43°C) £82	398	64 (57)
Monica 3	-	K2 700x800 1568W	T21 600x600 833W	K2 450x900 1234W	K2 450x700 959W	K2 600x500 866W	379	55	3.10
	51°C (53°C)	K2 700x800 1568W 51°C (51°C) £129	T21 600x600 833W 49°C (44°C) -	K2 450x1000 1371W 47°C (45°C)£100	K2 450x800 1096W 45°C (44°C) £87	K2 600x600 1039W 45°C (43°C) £82	398	55 (57)	3.10
Monica 4b planI	T21 600x600 833W 47°C (49°C) -	K2 700x800 1568W 47°C (48°C) £129	T21 600x600 833W 49°C (44°C) -	K2 450x1000 1371W 47°C (45°C) £100	K2 450x800 1096W 45°C (44°C) £87	K2 600x600 1039W 45°C (43°C) £82	398	52 (52)	3.24
planP	T21 600x600 833W	K2 700x900 1764W	T21 600x600 833W	K2 450x1400 1919W	K2 450x900 1234W	K2 600x800 1385W	482	52	3.24
Monica 4a	T21 600x600 833W 47°C (49°C) -	K2 700x800 1568W 47°C (48°C) £129	K2 600x700 1212W 46°C £89	K2 450x1000 1371W 47°C (45°C)£100	K2 450x800 1096W 45°C (44°C) £87	K2 600x600 1039W 45°C (43°C) £82	487	50 (52)	3.33
Monica 5c planM	K2 600x900 1568W	K2 700x800 1568W	K2 600x900 1558W	K2 450x1200 1645W	K2 450x900 1234W	K2 600x700 1212W	636	47	3.47
Monica 5a	K2 1800x600 2376W	K2 700x800 1568W	K2 700x1000 1960W	K2 450x1400 1919W	K2 450x900 1234W	K2 600x800 1385W	909	45	3.56
Monica 5d planN	K2 1800x500 1980W	K2 700x900 1764W	K2 700x1000 1960W	K2 450x1400 1919W	K2 450x900 1234W	K2 600x800 1385W	895	45	3.56

Radiator sizes using Octopus heat loss figures

Flow temperature 55°C (Monica 3)

For a radiator temperature of 51°C, the correction factor is 0.513 for a room temperature of 21°C, 0.581 for 18°C, and 0.491 for 22°C.

Room	Room temp °C	Octopus heat loss W	Radiator power for Octopus heat loss W	Possible radiator	Cost £
Lounge	21	1993	3885 = 2376+1509	K2 vertical 1800x600 2376W	-
Dining room	21	-		K2 700x800 1568W = plan L/I	129
Back room	21	1134	2211 = 1558+653	K2 600x900 1558W + T21 600x600 833W old lounge	-
Hall	18	352	606	T21 500x700 972W installed	-
Study	18/21	270	465	K2 600x400 693W	-
Front bedroom	18/20	687	1182	K2 450x900 1234W	94
Back bedroom	18/20	493	849	K2 450x700 959W	82
Ensuite	21	531
Bathroom	22	396	807	K2 600x500 866W	74
Total		5856			379

Daikin SCOP = 3.10

Flow temperature 50°C (Monica 4a)

For a radiator temperature of 47°C, the correction factor is 0.426 for a room temperature of 21°C, 0.491 for 18°C, and 0.404 for 22°C.

Room	Room temp °C	Octopus heat loss W	Radiator power for Octopus heat loss W	Possible radiator	Cost £
Lounge	21	1993	4678 = 2376+2302 = 2367+1568+734	K2 vertical 1800x600 2376W + T21 600x600 833W old lounge < planL/I	-
Dining room	21	-		K2 700x800 1568W = planL/I	129
Back room	21	1134	2662 = 1558+1104	K2 600x900 1558W + K2 600x700 1212W < planL/I	89
Hall	18	352	717	T21 500x700 972W installed	-
Study	18/21	270	634	K2 600x400 693W installed	-
Front bedroom	18/20	687	1399	K2 450x1000 1371W = planL/I	100
Back bedroom	18/20	493	1004	K2 450x800 1096W = planL/I	87
Ensuite	21	531
Bathroom	22	396	980	K2 600x600 1039W < planI/L	82
Total		5856			487

Daikin SCOP = 3.33

Flow temperature 47°C - plan M (Monica 5c)

For a radiator temperature of 44°C, the correction factor is 0.363 for a room temperature of 21°C, 0.426 for 18°C, and 0.342 for 22°C.

Room	Room temp °C	Octopus heat loss W	Radiator power for Octopus heat loss W	Possible radiator	Cost £
Lounge	21	1993	5490 = 2376+3114 = 2367+1568+1546	K2 vertical 1800x600 2376W + K2 600x900 1568W	102
Dining room	21	-		K2 700x800 1568W	129
Back room	21	1134	3134 = 1558+1566	K2 600x900 1558W + K2 600x900 1558W	102
Hall	18	352	826	T21 500x700 972W installed	-
Study	18/21	270	634	K2 600x400 693W installed	-
Front bedroom	18/20	687	1613	K2 450x1200 1645W	120
Back bedroom	18/20	493	1157	K2 450x900 1234W	94
Ensuite	21	531
Bathroom	22	396	1158	K2 600x700 1212W	89
Total		5856			636

Daikin SCOP = 3.47

Flow temperature 45°C (Monica 5a)

For a radiator temperature of 42°C, the correction factor is 0.324 for a room temperature of 21°C, 0.386 for 18°C, and 0.302 for 22°C.

Room	Room temp °C	Octopus heat loss W	Radiator power for Octopus heat loss W	Possible radiator	Cost £
Lounge	21	1993	6151 = 2376 + 2376 + 1399	K2 1800x600 2376W installed + K2 1800x600 2376W	289
Dining room	21	-	assume 1568	K2 700x800 1568W = plan L/I	129
Back room	21	1134	3500 = 1558+1942	K2 600x900 1558W installed + K2 700x1000 1960W	149
Hall	18	352	912	T21 500x700 972W installed	-
Study	18/21	270	699	K2 600x400 693W installed	-
Front bedroom	18/20	687	1780	K2 450x1400 1919W = Octopus	154
Back bedroom	18/20	493	1277	K2 450x900 1234W = Octopus	94
Ensuite	21	531	1639
Bathroom	22	396	1311	K2 600x800 1385W = planL/I	94
Total		5856			909

Daikin SCOP = 3.56

Dining and extra lounge radiators for flow temperature 45°C

Since Octopus lump the lounge and dining area together, there is some flexibility in the choice of dining and extra lounge radiators. The optimal choices would be balanced according to my heat model and hence give us the lowest flow temperature.

Octopus require a total radiator power of 6151W for the combined room (see above). The existing vertical radiator will provide 2376W, so the other two radiators will together need to provide 6151-2376 = 3775W.

My heat losses are 1417W for the lounge and 607W for the dining area.

The most balanced choice uses the K2 1800x500. This would give a flow temperature of aroumd 45°C using my heat loss figures.

Lounge radiator	Dining radiator	Min lounge radiator °C for my heat loss	Min dining radiator °C for my heat loss	Cost £
K2 1800x600 2376W £232	K2 700x700 1372W £129	41	48	£361
K2 1800x500 1980W £264	K2 700x900 1764W £140	42	43	£404
K2 1800x400 1584W £240	K2 700x1100 2156W £164	44	<42	£404
K2 700x1000 1960W £149	K2 700x900 1764W £140	42	43	£289

Minimum flow temperatures for various radiator sets

The tables below show minimum radiator temperatures. Add 3°C or 4°C to get flow temperatures.

Minimum temperatures based on Octopus heat losses use the room temperatures targeted by Octopus.
Minimum temperatures based on my heat losses target higher temperatures in the study and bedrooms.

planC - Current radiators (Monica 1)

Room	Room temp °C	Radiator	Octopus heat loss W	Minimum radiator °C for Octopus heat loss	My heat loss W	Minimum radiator °C for my heat loss
Lounge	21	K2 1800x600 2376W	1993	56	1417	56
Dining room	21	T21 600x600 833W		56	607	60
Back room	21	K2 600x900 1558W	1134	60	812	51
Hall	18	T21 500x700 972W	352	41	533	53
Study	18/21	K2 600x400 693W	270	42	554	62
Front bedroom	18/20	T11 400x700 460W	687	~87	500	74
Back bedroom	18/20	T11 400x700 460W	493	71	367	62
Ensuite	21		531		189
Bathroom	22	T11 600x400 410W	396	71	309	62

With the highlighed radiators replaced, a flow temperature of 64°C would be possible.

Not suitable for use with the Daikin heat pump.

planL radiators (Monica 2)

Room	Room temp °C	Radiator	Octopus heat loss W	Minimum radiator °C for Octopus heat loss	My heat loss W	Minimum radiator °C for my heat loss
Lounge	21	K2 1800x600 2376W	1993	51	1417	53
Dining room	21	K2 700x800 1568W		51	607	51
Back room	21	K2 600x900 1558W	1134	60	812	52
Hall	18	T21 500x700 972W	352	44	533	33
Study	18/21	K2 600x400 693W	270	42	554	62
Front bedroom	18/20	K2 450x1000 1371W	687	48	500	45
Back bedroom	18/20	K2 450x800 1096W	493	45	367	45
Ensuite	21		531		189
Bathroom	22	K2 600x800 1385W	396	<42	403	43

This configuration doesn't seem sensible, since the back room is so much worse than the other rooms.

planI radiators (Monica 4b)

Room	Room temp °C	Radiator	Octopus heat loss W	Minimum radiator °C for Octopus heat loss	My heat loss W	Minimum radiator °C for my heat loss	Cost £
Lounge	21	K2 1800x600 2376W + T21 600x600 833W	1993	47	1417	49	-
Dining room	21	K2 700x800 1568W			607	48	129
Back room	21	K2 600x900 1558W + T21 600x600 833W	1134	49	812	44	-
Hall	18	T21 500x700 972W	352	42	533	28	-
Study	18/21	K2 600x400 693W	270	42	554	62	-
Front bedroom	18/20	K2 450x1000 1371W	687	48	500	45	100
Back bedroom	18/20	K2 450x800 1096W	493	45	367	44	87
Ensuite	21		531		189		-
Bathroom	22	K2 600x600 1039W	396	45	403	43	82
Total							398

According to Octopus heat losses, these radiators would need a flow temperature of about 52°C.
According to my heat model, these radiators would need a flow temperature of about 52°C.

Daikin SCOP = 3.24

planM radiators (Monica 5c)

Room	Room temp °C	Radiator	Octopus heat loss W	Minimum radiator °C for Octopus heat loss	My heat loss W	Minimum radiator °C for my heat loss	Cost £
Lounge	21	K2 1800x600 2376W + K2 600x900 1558W	1993	44	1417	45	102
Dining room	21	K2 700x800 1568W			607	45	129
Back room	21	K2 600x900 1558W + K2 600x900 1558W	1134	44	812	39	102
Hall	18	P+ 500x700 972W	352	41	533		-
Study	18/21	K2 600x400 693W	270	42	554	62	-
Front bedroom	18/20	K2 450x1200 1645W	687	44	500	41	120
Back bedroom	18/20	K2 450x900 1234W	493	43	367	41	94
Ensuite	21		531		189		-
Bathroom	22	K2 600x800 1385W	396	<42	403	<42	94
Total							641

According to Octopus heat losses, these radiators would need a flow temperature of about 47°C.
According to my heat model, these radiators would need a flow temperature of about 48°C.

Daikin SCOP = 3.47

planN radiators (Monica 5d)

The ultimate future-proofing, with a 1800x500 vertical as the extra lounge radiator, and with upgraded radiators eleswhere.

Room	Room temp °C	Radiator	Octopus heat loss W	Minimum radiator °C for Octopus heat loss	My heat loss W	Minimum radiator °C for my heat loss	Cost £
Lounge	21	K2 1800x600 2376W + K2 1800x500 1980W	1993	42	1417	42	264
Dining room	21	K2 700x900 1764W			607	43	140
Back room	21	K2 600x900 1558W + K2 700x1000 1960W	1134	42	812	<41	149
Hall	18	P+ 500x700 972W	352	41	135	<38	-
Study	18/21	K2 600x400 693W	270	42	554	62	-
Front bedroom	18/20	K2 450x1400 1919W	687	41	500	38	154
Back bedroom	18/20	K2 450x900 1234W	493	43	367	41	94
Ensuite	21		531		189		-
Bathroom	22	K2 600x800 1385W	396	<42	403	<42	94
Total							895

According to Octopus heat losses, these radiators would need a flow temperature of about 45°C.
According to my heat model, these radiators would need a flow temperature of about 46°C, assuming we insulate the study.

The back bedroom radiator should really be 450x1000 to match Octopus heat loss, but Octopus underspecified at 450x900 - I'm not going to argue! They also underspecified the 600x400 for the study.

Daikin SCOP = 3.56

planP radiators

This is like planN, but uses the original lounge and dining room radiators are used as the extras in the lounge and back room.

Room	Room temp °C	Radiator	Octopus heat loss W	Minimum radiator °C for Octopus heat loss	My heat loss W	Minimum radiator °C for my heat loss	Cost £
Lounge	21	K2 1800x600 2376W + T21 600x600 833W	1993	46	1417	48	-
Dining room	21	K2 700x900 1764W			607	43	140
Back room	21	K2 600x900 1558W + T21 600x600 833W	1134	49	812	43	-
Hall	18	P+ 500x700 972W	352	41	135	<38	-
Study	18/21	K2 600x400 693W	270	42	554	62	-
Front bedroom	18/20	K2 450x1400 1919W	687	41	500	38	154
Back bedroom	18/20	K2 450x900 1234W	493	43	367	41	94
Ensuite	21		531		189
Bathroom	22	K2 600x800 1385W	396	<42	403	<42	94
Total							482

According to Octopus heat losses, these radiators would need a flow temperature of about 52°C.
According to my heat model, these radiators would need a flow temperature of about 51°C.

Daikin SCOP = 3.24

Hot water cylinder

See my notes on how to tell if a cylinder will fit in the airing cupboard. Basically, 1444 - 0.85 * H - W should be greater than zero, where H and W are the height and width of the cylinder in mm.

The heat pump cylinders on the Newark website are vented, so would not be suitable. They do manufacture unvented cylinders, but there are no details provided.

Model	Dimensions W x H mm	1444 - 0.85 * H - W	Price £ exc VAT
Newark

Octopus heat pump

Summary of possible radiator sets

Radiator sizes using Octopus heat loss figures

Flow temperature 55°C (Monica 3)

Flow temperature 50°C (Monica 4a)

Flow temperature 47°C - plan M (Monica 5c)

Flow temperature 45°C (Monica 5a)

Dining and extra lounge radiators for flow temperature 45°C

Minimum flow temperatures for various radiator sets

planC - Current radiators (Monica 1)

planL radiators (Monica 2)

planI radiators (Monica 4b)

planM radiators (Monica 5c)

planN radiators (Monica 5d)

planP radiators

Hot water cylinder