help sizing rads based on room by room heat loss
scratching my head a bit as to what size rad i need for a given room based on its heat loss. the system is designed to 40c flow @-3.1c outside. lots of sites list rad outputs based on delta t50, is this the flow temp? so if i can find out the output at dt40 for instance is that the output i need to match to this chart?
With a flow of 40C the dT for a 20C room temp is 20 it’s the difference in temp between flow and room. The output of a rad at dT 20 is 0.3 of its output at dT50
so why dont sites list the output based on flow temp? cause most seem to use dt.
Posted by: @adamkso why dont sites list the output based on flow temp? cause most seem to use dt.
Because they don't know your room temperature and it's only (average) DT that matters
Posted by: @adamkso does that mean at a dt of 50 the actual flow is 70c for a 20c room temp?
Not strictly I think. It's 20 plus half the DT between flow and return so that the average dt rad to room is 50
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @garyYep exactly that
jees ive got 2 hopes of heating my bathroom then. someone suggested an standard design aluminium rad, instead of a towel rad, but im worried in a copper and steel setup ill get galvanic corrosion.
I just left the old towel rail which is now way underpowered. I am relying on heat transfer from the adjacent hallway, which has excess capacity, together with steam when you run a bath/shower. It works just fine - the level of thermal separation between rooms is quite modest in practice.
Obviously this is house dependent but more than one prospective installer remarked to me that they frequently do not install a 'fully compliant' radiator in a bathroom (because of the low output of and desire for towel rails).
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
can i ask then if i have a heat loss for a room of 1079w and a flow of 40c@-3.1c what wattage rad do i need to hit? cause at the moment im struggling to find one big enough that would fit in the space.
The output of a rad is proportional to DT to the power 1.3, where DT is the average temperature difference between rad and room.
At a flow temperature of 40, and assuming a room temperature of 20 and a temp drop across the radiator of 5, DT is 37.5-20=17.5
Radiators are usually specified for a DT of 50. So you will need a rad with an output at DT 50 of (50/17.5) to the power 1.3 x 1079W = 3.9x1079W=4.2kW.
That's a mighty big radiator. What room is this in? Consider more than one radiator or a fan radiator if the loss really is that high.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@jamespa thanks for the info but I think I must have something wrong. The heat loss for the whole house is about 7.5kw. The room is only 3.756m x 3.686m. Current rad is a P+ 1450mm 380mm.
Posted by: @adamk@jamespa thanks for the info but I think I must have something wrong. The heat loss for the whole house is about 7.5kw. The room is only 3.756m x 3.686m. Current rad is a P+ 1450mm 380mm.
Have you got the loss calculations, if so perhaps you could post?
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
- 22 Forums
- 2,038 Topics
- 44.4 K Posts
- 53 Online
- 3,259 Members
Join Us!
Trusted Installers
Struggling to find a reliable heat pump installer? A poor installation can lead to inefficiencies and high running costs. We now connect homeowners with top-rated installers who deliver quality work and excellent service.
✅ Verified, trusted & experienced installers
✅ Nationwide coverage expanding
✅ Special offers available
Latest Posts
-
RE: Help with understanding my Mitsubishi Ecodan air source heat pump
@sunandair interesting, thank you. Is there any ...
By Patch , 16 minutes ago
-
RE: Commencing on an ASHP Installation Process
11kW does sound way over in that case! As you say it w...
By JamesPa , 2 hours ago
-
RE: Installing your own ASHP - DIY
Hi @tomasmcguinness, how are you progressing with this?...
By Ashfp , 2 hours ago
-
RE: Say hello and introduce yourself
Welcome to the forum. If you are new to ASHPs I sug...
By JamesPa , 8 hours ago
-
RE: Getting the best out of a heat pump - is Homely a possible answer?
@editor I have been with Havenwise for about three week...
By Broadsman , 8 hours ago
-
RE: Help me keep the faith with my air source heat pump installation
@editor guess the reason im asking is cause ive looked ...
By AdamK , 16 hours ago
-
RE: The Rise and Fall of Europe’s Most Generous Green Subsidy
This is where the cold water storage tank was situated;...
By Dwynwen , 1 day ago
-
RE: Air Source Heat Pump - Side Alley Suitability
Thats probably fair enough. The degree-days calculatio...
By JamesPa , 1 day ago
-
RE: ASHP Ecodan L9 error - No Heating but Hot Water
That’s interesting, but obviously concerning also…. Do ...
By SUNandAIR , 2 days ago
-
RE: In the middle of an ASHP installation - a few questions (and issues)
Thank you @robs - that very useful data. The issue wa...
By Transparent , 2 days ago
-
RE: Hitachi Yutaki SCombi Heat Pump - Thermal Off's
@trebor12345 The Auto function is supposed to adapt au...
By Heatgeek , 3 days ago
-
RE: The Great British Heat Pump Quiz
@allyfish thanks for the feedback and glad it was fun! ...
By Mars , 3 days ago
-
RE: help sizing rads based on room by room heat loss
If its 1988W at DT 50, which is how most radiators are ...
By JamesPa , 3 days ago
-
RE: Career change – entering the world of heating and heat pumps
@editor Mars, thank you. That's along the routes I was ...
By Lakey , 3 days ago
-
@editor thanks Mars, it's a rare occasion I'm looking f...
By big_si , 4 days ago
-
RE: Efficiency Concerns on newly installed Mitsubishi Ecodan 8.5kW
@ashp-bobba and @jamespa - thank you both for all your ...
By CBrenewable , 4 days ago
-
-
Win one of five "Heat Pumps 101" Courses
Heat pumps are gaining traction in the UK, but between ...
By Mars , 4 days ago
-
RE: Agile: average import cost vs other tariffs?
@toodles thanks for the analysis. I'll be really intere...
By Old_Scientist , 5 days ago