The best way to check a heating system is to run it at a low temperature for a winter and see how it performs, which rooms are cold when. This will give a perfect starting point when looking to install a heat pump.

I was lucky, the boiler started playing up just as my single panel radiators started to rust. So new heat pump and new radiators all round.

I do think you are somewhat underplaying the potential role of greater insulation. If the radiator in a room can't supply enough heat to match the heat loss of that room at you new lower flow temperature there are two options, increase the output of the radiator by replacing it with one that is bigger/more effective, or reduce the heat loss of the room until the existing radiator can meet the requirement with the lower flow temp. The first option will increase the COP of the pump but without reducing the overall heat required, the second will increase the COP AND reduce the overall heat requirement, a double benefit. Both options will involve some cost, but surely you should look at the option of increasing the level of insulation first?

Very useful guide, thanks!

I am thinking about adding underfloor heating on every floor before switching to a heat pump. The bedrooms now have T11 radiators (installed 1989) and the living room is now on T22 radiators. When not home or if the room is not used, we let things cool down. An on some very cold days the boiler needs to go up to 60c to make the room warm enough in a reasonable time. Also, windows in the bedrooms are left open for way too long, and i have given up on changing her mind about that behaviour. Other rooms are fine at 50c because of recent insulation efforts and often much lower if weather permits. The gas boiler is quite recent (Q1 2020) and i have tuned it down to about 4 kW to prevent on/off problems. I am considering a Vaillant R290 system, but because of all your advice, I think upgrading to underfloor heating first on the gas boiler and measuring coming winter may be a better way to be sure about the sizing. My question: Would you leave these T11 radiators installed in bedrooms so they can contribute to the size of the system and recover fast from excessive ventilation, just remove them or even replace them with bigger ones in the bedrooms to add to or replace underfloor heating? The living room floor is a bit worn, and the T22 radiators are ugly, so underfloor heating is pretty much a no brainer there.

just brilliant advice

Google knows doesn't it? This is EXACTLY what I was just wondering about. Ballpark conversions from the catalogue spec. Wouldn't it be grand if manufacturers gave outputs for perhaps 3 flow temps? Thanks again Adam. 👍🍻

Thank you. Both this and the previous information I watched has made me more confident to book an engineer to see if the property is suitable. knowing a bit about how things work etc is so helpful.

Loving all the videos & articles on your website - very informative stuff. I have recently become a big HG fan :) Apologies for what could be a bit of a noob question on an old-ish video, but I'm having trouble reconciling the differences in outputs between the DT20 and DT30 cheat sheets: my understanding is that the output changes as the ratio of the DTs raised to the power of 1.3, so Output of rad at DT20 = (Output of rad at DT30) x (20/30)^1.3 Using the outputs given in the DT30 table, this would yield the following outputs for DT20: Type 11: 800 x (20/30)^1.3 = 470 W/m^2 Type 21: 1140 x (20/30)^1.3 = 670 W/m^2 Type 22: 1500 x (20/30)^1.3 = 885 W/m^2 Type 33: 2200 x (20/30)^1.3 = 1300 W/m^2 Appreciate that there is a bit of rounding going on, but all of these calculated figures are a good 15% lower than those in your DT20 cheat sheet table. Is it possible that for the DT30 table the MWT of the radiator has been used, but in the DT20 table the flow temp has (mistakenly) been used? e.g. if the deltaT between flow & return is 5K then the flow temp is 2.5K above the MWT. If we plug a DT of 22.5K into the formula the following outputs are calculated: Type 11: 800 x (22.5/30)^1.3 = 550 W/m^2 Type 21: 1140 x (22.5/30)^1.3 = 785 W/m^2 Type 22: 1500 x (22.5/30)^1.3 = 1030 W/m^2 Type 33: 2200 x (22.5/30)^1.3 = 1515 W/m^2 These figures are much closer to those quoted in the DT20 cheat sheet, so I wonder if that's what's happened here?

Thanks

Hi, I was interested in the free energy video using solar thermal with heatpump backup. Can you do more about the setup you have and the cost. How often have you managed to use just the solar thermal and other than the heatpump what other inputs do you have in the system. I don't think the tubes alone would be enough?

Great video - can you extend your cheat sheet for Type 20?, just plain double panels?

and really well presented

What a fantastic video. Answered questions I didn't even know I had. Looking to install an ASHP in my really cheap house in a remote village with no access to mains gas and only unreliable mains power. The house has 2No. 20m2 rooms and a roughly 7m2 pantry which will be converted into a bathroom and small kitchenette temporarily will we build a much bigger extension. Thankfully we'd be able to fit 1.6m long radiators in the main rooms which should help a lot with heating and keeping electric costs down/solar usage down, especially in those winter months.

Hi there, really helpful and informative video. Just wondered how to work out what wattage you would need for the room?

Watched loads of your videos. Very informative! I'm thinking of replacing my old boiler in an Victorian detached. I saw in one of your more recent videos that you've used fans to increase the flow of air through the radiator. I was wondering if fans could be a cheap way of effectivity increasing the output power without physically having to swap out a radiator? The idea being to run the radiator at a lower temperature than a boiler would have needed?

Thanks, another really helpful video. Hopefully a simple question… the required output for a room can be spread across multiple rads? E.g. if it’s easier to put in a second rad rather then make/find space for a larger rad?

Thank you most useful

I’ve just started a self build using the ICF blocks and was thinking of using an air source heat pump instead of Gas boiler for heating and hot water. Not sure if it’s the best move or not??

Great Video as always. You mentioned Flow temp or is this MW (e.g 55/45) on the Rad outputs

Hi, your video is great. We just moved in to a new house with Air to water heating system with heat pump. We upgraded the bathroom and decided to change radiator in bathroom with Vertical towel Rock radiator. When we remove the original radiator water pipe coming from the ground one side longer then the other side and that makes vertical radiator not level. We need to cut pipe few cm to Level the connections and radiator. Do l have to switch off everything and draining boiler radiators all system to cut pipe few cm? Will it cause problem to system wondering? What would you recommend?

Our house is a 2007 build with (I believe) 15mm pipe work. Our boiler system is a Worcester Greenstar 30CDI system. I appreciate we will in all likelihood require larger capacity radiators but will the existing pipe work be sufficient for a ASHP. The house is well insulated but I’m not sure what thermal efficiency band it is in.

I heard that you can retrofit convection to existing radiotor, i.e., a few little fans underneath the panels and blow up automatically when temperature of the radiator rise. any comment? thanks

What about convertor type 'radiators' like e.g. Jaga makes? Since we have those it would be indeed be a very handy cheat sheet if it included these!

Thank you again, legend. This is timely info for me 🙂 One question about the material the rad is constructed from: I see aluminium rads which claim a higher output due to its better conduction... What are your thoughts on those - Are they worth the upgrade? Is there a rule of thumb % output difference per m² Vs steel?

I've turned the flow temperature on our gas condensing boiler to 40C and the house is still comfortable. It's been like that since January. Am I right to assume that this means the system is suitable for a ASHP or are there other factors? Flow rate perhaps??

Question regards high temp heat pumps: If you have proper weather compensation, presumably when the weather is fine to run at 40c, it will do that, and be as efficient as any other heat pump? I ask cos my rads on gas boiler are fine at 70c down at -5 or so, and on the one occasion I remember it being colder than that, 80c (Mac boiler flow temp) was fine. But that's compensating for some rooms that are barely adequate radiators now. Other rooms do much better - though still not low flow rates at -3. But once we get above about 4c I can run the system at 60 now, above 8 at 55, and above 10 50 does the job. If I upgraded the worst rooms to perform as well as the best, those -3 days would only require 60c, and 70 below that would be fine unless things got into double digits below. And the rest of the time 45-55 would be fine. Upgrading all my rads to meet low temp at -3 will cost about 3k. Upgrading as above less than a thousand. If a high temp heat pump can cope with the spike periods needing 65c+ for maybe 20 days a year tops, but run low temp the rest of the time, that would seem like a reasonable trade off Vs an extra 2.5k upfront cost on rads (depending on the cost of the hthp of course).

Does this cheat sheet work to radiators connected with 10mm flexible piping? We have a new build where they used this and have been told the pipe work will need replacing.

Do I need to take into account the dust,webs and old socks in my fins on my rads for my equations lol

Hi. Thanks for the video. What's your opinion on column radiators please? Which type would be closest comparison for your cheat sheet? I've read an article that suggests they are potentially better than panel + convector fin types, despite sometimes being rated with lower BTU figures, because they have a greater direct surface area. Is that true?

Structured well to understad - thank you! I noticed that you did not talk about low temperature aluminium radiators for use with Heat Pumps. Is there a reason for that?

Hi Heat Geeks I've heard you comment before about under floor piped heating being preferable to radiators. However the challenge I have is that the 1950's home I'm purchasing has concrete floors, throughout the ground floor. My questions are: 1) Do heat pumps require greater in diameter pipes under the floor than a gas powered under-floor heating system? 2) What diameter pipe sizes do you recommend. 3) Instead of raising the floor I'm considering cutting groves in the concrete, hopefully finding an insulation matting that would sit inside the groves, and cover the remaining un-grooved floor. This has the benefit of not requiring to screed the floor, just an underlay and hardwood flooring on top. I suppose my second question is, what do you think of my cunning plan? Any pointers would be gratefully received,. By the bye, I may end up cutting the grooves to keep costs down, but I intend to have the fitting and commissioning completed by one of your Heat Geek professionals, found on your map, in Chelmsford. Kind regards Robert

Hi Adam. Thanks for the very handy calculators. I want to start with replacing one radiator in my house, because it seems to be undersized compared to the rest of the radiators. I've followed your advice and turned the flow temperature down on my gas boiler, and all the rest of the rooms in the house heat up nicely at the low flow temperature, but my sitting room takes hours to heat up to 21 degrees, and sometimes never quite makes it and I only let it drop to 20 at night. So I can either turn back up the flow temperature to heat that room, or have the boiler running almost constantly for that one room. I've opened the lock shield fully on this radiator. When I replace that radiator, should I aim for a radiator size that works at a flow temperature of 40 degrees, to future proof for a heat pump, or would this now put this radiator out of balance with the rest of the radiators, and cause me problems? Thanks

The house we bought had a 16kW heat pump and we are going with the downstairs as underfloor heating and the upstairs having radiators fitted. We already have the power chart in kW needed to heat the each room but, we are going to install aluminium rads potentially. Watts are watts at the end of the day and just as long as the new rads can accommodate that power needed it shouldn’t be a problem should it?

Most of my radiators are single panel with no fins - what would their output be?

So should I open the curtains when the heating is running?

Good video, enjoyed your commentary on heat pumps thus far. Please don't limit people to type 11,22 radiators, there are many beautiful designer radiators that can work on heat pumps effectively and achieve the outputs at lower flow temperatures, no need for dull corrugated steel panels.

Good video. Is the 40 degree chart mean 40c mean water temp, so a 50 flow 30 return, mwt40 minus 20 room temp is dt20 for gas boiler? Are is the flow and return dt on an ashp much closer together?

I have cast Iron rads how do I calculate for these

For the sake of comparison with an existing old install, what would be the ballpark heat output per m2 at 50C of single and double panel radiators without convectors ?

Interesting video, thank you. What are your thoughts on 'retrofit' underfloor heating? The sort which goes on top of your existing slab. Worth the effort over posible upsizing radiators?

If I'm right in thinking that water flow is important in a heat pump system and that the restriction of microbore pipe work may be a hindrance and also that a heat pump system is generally on for most of the time then whats the point of lock-shields on the rads? or put it another way, the hole even when fully opened is less than the width of micropore so must be just as restrictive. I'd be really interested to know your thoughts. Thanks for the content.

Heat loss calcs are always going to be of dubious accuracy in an existing house with all the unknowns including insulation spec and build quality under the surface. As per a previous suggestion, surely a simple and accurate method to assess compatibility for a heat pump would be to run the existing boiler at 50 degrees during sub zero weather and make a judgement on whether the rooms stay warm enough. Perhaps you could point out any flaws in that strategy Heat Geeks.

I am finding it difficult to understand that if my existing gas heating which is on 1 hour in the morning and 4 hours in the evening uses about 60kW to heat the property, but nothing during the day as it gradually cools. a heat pump has to deliver 70kW to get the same amount of heating, so the sCOP has to be 1 to 3.5 to cost the same as gas. However, my understanding is the heat pump has to be on all the time. If I assume a heat pump is on all the time using 1kW of power to give 3.5kW continuous heat to my house (which I don't think will keep a 5 bedroom properly warm)...I am now using 24kW of electricity. The gas heating also heats my water within that 70kW. The heat pump can't do that at a SCOP of 3.5...so how do I save money?? I do have a large loft conversion, well insulated and I actually have an inverter split system up there...if when it's cold I warm just that room, that one system alone uses around 380W, after it's got the room up to temperature. I have the outside unit mounted up at around 7ft high to avoid the cold ground effect. So I'm thinking 1kW consumed definitely won't heat the whole house for a heatpump system?

U said in one video don't use plastic pipe for heating and u have a video on this. ?

Given that emitters are the single biggest determining factor in the performance of a heat pump. Have you considered testing the ThermaSkirt system? It is effectively a radiator just in a different shape. We've run it at low temps for years.

Great video but I am missing something fundamental. For a Type 22 rad you quote 1500W/M2, so for a 0.72m2 rad the output would be 1080W , yet when I look at a rad chart in the Screwfix specification it is quoting 2112W at DeltaT50degC what am I missing here?

So type 21 rad at 40C = 800*0.6*1.6 = 768 watts thats getting close to spec for my living room =) (600mm x 1600mm)

What about actual radiators (not convectors) meaning: column radiators or cast iron radiators. If they are new or in good order, can they be used for a heat pump? I guess the output is usually too low at say 40 or 35 degrees, because there is only radiation, no/almost no convection. Or is this more of a match for high temperature heat pumps. Maybe a video on that rare beast of the pump breed?

Great info, but what about a 30°c or less flow temperature?

Can't I just swap all my type 11's for 22's, and double up the 21's for 2x the same size in 22's? Job done :) All my rads need replacement anyway...

Are the cheat sheet values exactly or approx? Because I did work some out from a Kudox radiator data sheet and the heating output in w/m2 worked out slightly higher. e.g. type 22 DT30 worked out to be 1557.7w/m2 instead of 1500w/m2, this can be crucial in some cases as sometimes you can get away with a type 22 instead of upgrading it to type 33.

Hi Guys could you tell me if cast Iron rads work with ASHP ? thank you for any help you can offer

1. Are aluminium rads better ? 2. Do vertical rads of same wattage expect to perform similar to horizontal ones? I am planing to get heat pump over the next few months and dont want to skimp on cost of rads as they are probably the least expensive part in the system.

Hey Heat Geek, Is it possible to do underfloor heating without any screed? I would like to install tiles all over my house floor. I have seen electric underfloor heating installation without screed, but I have not seen it with water heating pipes. Can you explain it more?

I'm building new house. HP 7,2 kw. Engineer calculated that house has heat loss 7,2 kw at -9,8 c and calculated radiators dimensions for HP. Dont want floor heating, dont ask me why. Now, what interests me is can I make my radiators even bigger than engineer calculated. To run them at lower temperatures? Would I need stronger HP then because I guess bigger radiators mean bigger water flow?

Hello. Really helpfull info ! I have a question though: you mention to calculate for a type 33 rad, at 40 degrees water, an output of ~1500W/m2. Based on the specs for a Purmo rad (good quality, overall), the output is 1360W/m2, but with 65 degree water. Quite a difference. Am I missing something?

will running radiators at these temperatures get my house warm when i only time it for 1 hr am and 2hrs pm?

all very with heat geek assured installers,but when i ran my address there is no one within 100 miles who is certified so no dice for me unfortunately :(

Use 22 downstairs and 21 upstairs. Works fine.

How about using a high temp heat pump, I’ve 27kw of battery storage that I charge on cheap rate electricity. Why because my pipes are microbore plastic and to replace in a new build would be hell. No one as yet has come up with and answer to new builds that mostly are piped with microbore plastic.

Can you go too big on radiator size?

Thinking of getting an air heat pump. Prob going to go for underfloor heating downstairs and then considering radiators upstairs on cost and because we'd want carpet on the first floor. Assuming insulation decent downstairs and given heat rises, will upstairs generally get decent residual heat from downstairs to compliment the radiators? Or is it worth the extra investment for the UFH upstairs under the carpet? Any advice or where to look would be great.

The best radiator for heat pump is "Anit Radiator " specially designed for low temperature

Inspired by your video, I've created a calculator in an excel spreadsheet which I'd like to share with you so you can host it on your site - I can't find an email address however. If you let me know, I'll ping it over. Thanks!

Why -2 or -3? What about -20?

Just a needed correction - the size/Kw of the radiators is calculated at 60C of the water inside and DeltaT 20 ! Bear in mind Also, fan coils to be considered instead of radiators is appropriate, as they need 40C water to operate correctly!

Cast iron rads? Aren’t these more efficient? That aside huge rads, in period properties, aren’t viable. Underfloor is the option to make these system work properly. Again not possible in many period properties, and too expensive to retrofit in most circumstances. Properties that need to be made more efficient for environmental and cost reasons are period properties. New builds can be passive and therefore require no, or very little, heating. These systems aren’t the answer the problem. I’m afraid it’s a red herring. The question is why aren’t new builds passive, and what is a more effective option for period and ancient houses.

Math geek

this is why ashp will never take off as the govt wishes - too complicated, too expensive and note suitable for most of the uk's badly insulated housing stock.

Thanks