Glycol

[JohnMo]

1 hour ago, Marvin said:

heater

The heater in the crankcase is there to keep oil temperature higher than refrigerant dew point, to stop oil dilution. That is it's sole purpose 

[ProDave]

6 hours ago, JohnMo said:

Here is one sensible review on glycol 

https://renewableheatinghub.co.uk/do-air-source-heat-pumps-really-need-glycol/

So the summary of that is it does not happen often, and if it does freeze your house insurance will cover it.  They don't cover the long power cut situation.

 

Sorry I don't want to be having the "you know it gets cold why did you not put antifreeze in" argument with my house insurer.  Not have the long period without heating while we argue.

 

What's this antifreeze must not be harmful in case it leaks into the drinking water?  NO different to any normal boiler that has some form of inhibitor.  Is that also potable just in case?

[JohnMo]

All this stuff is down to personal preference, risk profile etc, no right or wrong answer 

29 minutes ago, ProDave said:

What's this antifreeze must not be harmful in case it leaks into the drinking water?

Two sorts of glycol, the stuff you put in the car - highly poisonous. The stuff you put in heating systems not poisonous.

 

30 minutes ago, ProDave said:

Is that also potable just in case

Yep

[sharpener]

58 minutes ago, JohnMo said:

Two sorts of glycol, the stuff you put in the car - highly poisonous. The stuff you put in heating systems not poisonous.

 

Four sorts

 

Stuff you put in your car - ethylene glycol based, highly toxic

 

Stuff you put in your heating system : 

• if ethylene glycol based (Fernox EG), highly toxic
• if EG based but with detox inhibitor (Hydratech Thermox DTX) then not toxic
• If propylene glycol based (Sentinel X600) then inherently non-toxic.

[Nickfromwales]

11 hours ago, Marvin said:

A concern would be the starting up of the ASHP if it was frozen.

If it freezes, the joints all pop off everywhere and it loses pressure, ergo, it won’t start back up due to it then locking out.

[Potatoman]

How do you know what type of glycol you have in the system, and if you can't does it matter.

[Nickfromwales]

4 minutes ago, Potatoman said:

How do you know what type of glycol you have in the system, and if you can't does it matter.

Have the installers been kind enough to peel the sticker off the bottle and apply it somewhere for your information? Usually a sticker the size of a matchbox, or so. 

[Potatoman]

12 minutes ago, Nickfromwales said:

Have the installers been kind enough to peel the sticker off the bottle and apply it somewhere for your information? Usually a sticker the size of a matchbox, or so. 

Unfortunately not 😔

[JohnMo]

42 minutes ago, Potatoman said:

How do you know what type of glycol you have in the system, and if you can't does it matter.

Glycol is only part of the ingredients in the glycol tub. There is also the corrosion inhibitors etc these may or may not be compatible. Using a car antifreeze as an example, they are dyed a different colour to indicate compatibility i.e OAT (Organic Acid Technology) based chemicals are coloured orange.

 

So you ideally need to match the chemical makeup otherwise you can cause more issues than you solve.

[Gus Potter]

On 07/10/2025 at 07:48, JohnMo said:

But did you have a comment to make on glycol?

 

Sorry but to answer your comments.

 

What complexity I am just using the default settings for the ASHP.  There are no apps, they are not needed and add nothing, it doesn't need updating and fiddling with. It just sits there and gets on with it.

 

There are no fancy valves, only a 3 port diverter for DHW heating. In fact the system only consists of ASHP (with it's controller in the side of the ASHP), diverter valve, cylinder and UFH manifold. No additional pumps (other than one in ASHP) no mixers, no UFH manifold actuators, no fancy stuff at all.

 

But using an ASHP, so an advantage in running cost with variable flow temperature. Thermal stability of the house and reaction time of the UFH are pretty closely matched when running variable flow temperature. But can quite easily make the system work at a set flow temp and a thermostat, but house temp fluctuates more, due to the heat pump having to play catch up, to heat 19.2m³ of concrete. With WC flow temp changes preempts how the house will respond, all very simple, nothing complicated, it actually allows a much simpler system.

 

Yes I live in Scotland, not many places get the -20 anymore, still get variable seasons in 24hrs.

Hi John. 

 

Good post, I may need to eat a bit of humble pie here but happy to do so as I'm not always right, I have an opinion, but if you ask ten designers you'll get ten different answers! Anyway as you say "it just gets on with it" and that is the key. 

 

OK you have weather compensation.

 

Fine by me ( I do my own UF heating system), as it's a litle bit of "tech" which I'll be the first to admit is good fun to play with ( first slice of pie) but there are too many folk on BH that are using and desinging UFH using loop cad and stuff but none of that takes into account that you may put a rug on the floor or have a big sofa that sits close to the floor level!

 

So while folk think I'm living in that dark ages, have an axe to grind, I don't, I'm just saying.. hey the UFH maths is often a lots of bollocks when it comes to building it and making it work for 50 years or more. The maths may work on day one but then it is all down hill as you need to get someone to install it! And, as this is the building trade that is a challenge! 

 

I can back this statement up with examples of how I have found UFH systems that are design by sales folk rather than Enginners. I can point to a hospital, domestic stuff.. I can argue my case so I'm open to anyone on BH that can turn round and say to me.. hey I have UFH and it's been in 30 years and it's working well and here is what it costs us to replace parts. You see.. I know as I have this data on a couple of jobs that I look after! 

 

What I do as a design engineer is to look at the maths, how things actually work in practice and make an enginneering judgment based partly on maths and partly on practical and long term experience. 

 

Now I do a few insulated "passive raft type designs as an SE " and a well designed and durable UFH system starts from the ground up. It's something that I plan for as an integrated design. 

 

Next is that folk are using a computer to produce nice pipe layout diagrams but not realising how often that won't get translated on site with the trades folk actually doing the work. Yes, if you want to stand over them all day, hold them to the contract.. but the reality is that this will lead to a falling out on site, it does on big strictly supervised contract but self builders don't have the money or expertise to pay for this level of supervision. 

 

@JohnMo

"There are no fancy valves, only a 3 port diverter for DHW heating. In fact the system only consists of ASHP (with it's controller in the side of the ASHP), diverter valve, cylinder and UFH manifold. No additional pumps (other than one in ASHP) no mixers, no UFH manifold actuators, no fancy stuff at all."

 

Ok second slice of pie for me. I missed you spelling that part out. It looks to me that your system comprises stuff you can buy from screwfix. That to my mind look like something simple, easy to maintain and long lasting. There will be some on BH that say.. hey it not totally efficient but over even an 8 peroid I bet you maintenance costs will be lower than lots of folk on BH that are trying to get UFH to do something that it is not suited to do.

 

@JohnMo

"Yes I live in Scotland, not many places get the -20 anymore, still get variable seasons in 24hrs."

 

Don't bet on it John. My sister lives on Tiree and has two tandem ASHP to run a big house. The winter temperature is like you could grow palm trees.. the ASHP just run at their best speed, but that said, if there is a little shift on the Altantic sea currents.. it could be see a change, or if we get a wierd wind from Norway.. don't count your chickens just yet!

 

 

Edited October 14 by Gus Potter

[JohnMo]

@Gus Potter

The other simple way to run the UFH is again all open system and if thick screed is a simple low hysterisis thermostat or via ASHP controller if it has a built-in thermostat. Set thermostat to 20.5 to 21 and ASHP to fixed flow temp of 32 to 36. And then let the thermostat run the system. With UFH and a new build those flow temps will give great cycle times and run once per day most of the time. Pretty good CoP. Run time will vary with outside temperature. Then you also have room to oversize the heat pump easily, without causing to many issues just incase we get the -20 degs.

[MikeSharp01]

On 09/10/2025 at 09:27, JohnMo said:

Here is one sensible review on glycol 

https://renewableheatinghub.co.uk/do-air-source-heat-pumps-really-need-glycol/

Interesting link!

 

Just got told by our ASHP supplier that Glycol is a requirement of their guarantee! I re-did my flow / heat output calculations and found that 30% of their chosen Glycol will push my pump head requirement up by approx 100% I am now looking seriously at antifreeze valves! We sort of had this discussion back in 2022/23 (and occasionally since.. 

Not sure we reached any conclusions but the additional pump head requirement does not seem to have been featured very highly in the discussion while the difference in heat transfer does.  

[SteamyTea]

On 14/10/2025 at 22:14, JohnMo said:

Using a car antifreeze as an example, they are dyed a different colour to indicate compatibility i.e OAT (Organic Acid Technology) based chemicals are coloured orange.

Often wondered about that.

I did ask for my system to be completed flushed out at the 100k mile service (and it was).

Think it is pink.

[sharpener]

50 minutes ago, MikeSharp01 said:

30% of their chosen Glycol will push my pump head requirement up by approx 100%

 

From my earlier researches ISTR 30% is quite a high concentration for the UK, and in particular

 

Fernox HP-5C may be more economical, it can be used at a dosage as low as 10%, this protects down to -4C and has a specific heat of 4.15 at 55C. It is based on propylene glcol, but at a low conc. maybe the viscosity is not too bad. From the graphs it seems to be less viscous than 25% of Fernox HP-EG, which is the lowest allowable conc. of their ethylene glycol product.

 

Who is yr HP supplier and what product have they "chosen"?

 

[MikeSharp01]

32 minutes ago, sharpener said:

Who is yr HP supplier and what product have they "chosen"?

Coolenergy CE iH6+ and Thermox DTX. My problem is our longest loop at 185m of pipe over 40m2 of floor. I put it in when I expected a solid polished floor and thought the 1.5m head loss would not be a problem but now we are going for a wood floor with a TOG of 1.5 so the picture is very different. 

[sharpener]

3 hours ago, MikeSharp01 said:

Coolenergy CE iH6+ and Thermox DTX

 

Is there no room for negotiation? 22% of DTX will protect down to -10C so 30% prob. to -13 or so. That seems overkill for "East Kent" unless you are high up on the Weald...

[Nickfromwales]

17 minutes ago, sharpener said:

 

Is there no room for negotiation? 22% of DTX will protect down to -10C so 30% prob. to -13 or so. That seems overkill for "East Kent" unless you are high up on the Weald...

Most will go ‘bonkers’ to protect the system as their arses are in the sling if the system fails and the dilution is deemed to be the cause of the issue; if it’s investigated and found to have been too close to the wind / insufficient. 
 

Not so much of an issue if CE are supplying and installing and then servicing and maintaining it, but a different kettle in other circumstances I’d guess. 

[MikeSharp01]

7 hours ago, sharpener said:

Is there no room for negotiation? 22% of DTX will protect down to -10C so 30% prob.

Yes I think there is, I am 'in negotiation' now. 22% is a good compromise perhaps and -10 is plenty down here. I think I need to look at the delta T because that has a big effect on the head loss, I just need to keep the interface (between the screed and the wooden floor) temperature below 25 degrees C to meet the guarantee on the floor so its not going to be big if I want 21 deg C room temperature is it.