Glycol

[Potatoman]

Hi, what's the best way to add glycol to the heat pump system.

[IGP]

Best way is to not, and use anti freeze valves instead.

[JohnMo]

As above just don't do it. It's not needed, makes your pump run harder than it needs to and heat transfer isn't as good. Just do inhibited water.

 

I haven't even bothered with anti freeze valves. We just run weather compensation so everything is always active. So as you don't live anywhere that gets several day long power cuts and it's stays well below zero at the same time nothing much is going to happen.

[sharpener]

I dimly recall advice to pre-dilute it as it is quite viscous and may sit at the ends of branches and not mix. I think you can add it to flushing machines but I don't know of a handy DIY technique.

[Potatoman]

Unfortunately, I need to keep an eye on the glycol levels in my system as it is a hybrid system with an oil boiler which comes on at about +5 degrees C, so I am going to need frost protection. At the moment I am using a refractometer and draining a radiator and topping up with glycol, if it needs topping up, Just wondered if there was a better way. 

[JohnMo]

38 minutes ago, Potatoman said:

Unfortunately, I need to keep an eye on the glycol levels in my system as it is a hybrid system with an oil boiler which comes on at about +5 degrees C, so I am going to need frost protection. At the moment I am using a refractometer and draining a radiator and topping up with glycol, if it needs topping up, Just wondered if there was a better way. 

Your heat pump circulation pump will come at 3 or 4 degrees like it not to perform frost protection to look after itself. The only freeze protection needed is from a prolonged (several days with no electricity and sub zero). Oil boilers themselves never have (almost all) never run with glycol or anti freeze valves.

[Gus Potter]

1 hour ago, JohnMo said:

I haven't even bothered with anti freeze valves. We just run weather compensation so everything is always active.

I did my first UFH design in the country and it was minus 20 -23 degress below zero for three days in a row once.  The heating system was running full on anyway as I knew that any less insulated weak spot on hidden pipes would cause havoc. 

 

We knew the weather was coming.. did not need weather compensation. If you live in Scotland the weather changes by the hour so weather compensation, fancy valves, software are a lot of bollocks. The extra cost of just turning it on full bung for a few days far outweighs adding complexity to the system in the grand scheme of things. Also, see the time you need it.. that is sods law when it will probably break and the more complex it is the more chance it will break down. 

 

@JohnMo Yes, agree in part,  you may have the time to manage your weather comp.. but what about young folk that have a couple of kids, managing a lot of that.. they don't have time to ponce about with the weather compensation and adjust it, update the apps and shite. There will come a time when you valves and controls get "sticky" best of luck to you! 

 

So I'm going to keep being a philistine on UFH. Keep it simple, design in redundancy in your UFH pipe spacing. Think about preserving the asset value.. you'll have to sell the house at some point and the heating needs to work!

 

 

[JohnMo]

8 hours ago, Gus Potter said:

I did my first UFH design in the country and it was minus 20 -23 degress below zero for three days in a row once.  The heating system was running full on anyway as I knew that any less insulated weak spot on hidden pipes would cause havoc. 

 

We knew the weather was coming.. did not need weather compensation. If you live in Scotland the weather changes by the hour so weather compensation, fancy valves, software are a lot of bollocks. The extra cost of just turning it on full bung for a few days far outweighs adding complexity to the system in the grand scheme of things. Also, see the time you need it.. that is sods law when it will probably break and the more complex it is the more chance it will break down. 

 

@JohnMo Yes, agree in part,  you may have the time to manage your weather comp.. but what about young folk that have a couple of kids, managing a lot of that.. they don't have time to ponce about with the weather compensation and adjust it, update the apps and shite. There will come a time when you valves and controls get "sticky" best of luck to you! 

 

So I'm going to keep being a philistine on UFH. Keep it simple, design in redundancy in your UFH pipe spacing. Think about preserving the asset value.. you'll have to sell the house at some point and the heating needs to work!

 

 

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.

[ProDave]

I will be the odd one out then.  I have Glycol in my system.  I do NOT want the heating on 24/7 I prefer it off most of the night and prefer it to do most of the work in the day when the PV is likely co be contributing.

 

I do NOT want an anti freeze valve that will dump my water if it gets too cold.  

 

Glycol added at the ratio that will protect the system down to -10C

 

Never been a problem.  

[Kelvin]

1 hour ago, ProDave said:

I will be the odd one out then.  I have Glycol in my system.  I do NOT want the heating on 24/7 I prefer it off most of the night and prefer it to do most of the work in the day when the PV is likely co be contributing.

 

I do NOT want an anti freeze valve that will dump my water if it gets too cold.  

 

Glycol added at the ratio that will protect the system down to -10C

 

Never been a problem.  

Agreed. I read all the pros and cons and decided to add it for the same reasons as you. 

[Michael_S]

The only advantage for me is that should you get that long power cut or a system failure you don't have to drain the HP to protect it.  Downside of course is the reduced efficiency in heat transfer.  We are running a second circ pump (due to undersized pipes) so it is only the prolonged power cut that might cause us a problem whereas adding gylcol would definitely result in a reduced heat transfer rate problem.

[Potatoman]

10 hours ago, ProDave said:

I will be the odd one out then.  I have Glycol in my system.  I do NOT want the heating on 24/7 I prefer it off most of the night and prefer it to do most of the work in the day when the PV is likely co be contributing.

 

I do NOT want an anti freeze valve that will dump my water if it gets too cold.  

 

Glycol added at the ratio that will protect the system down to -10C

 

Never been a problem.  

So if you found the glycol in your system was too low, how would you top it up?

[gmarshall]

I have one of these, not a bad bit of kit for the price. Not sure it would stand up to daily use but for an occasional top up for whatever reason its a good option. I also used ours for pressuring the UFH when we were doing our refurb. Ours can be coupled to the UFH manifold or with a suitable fitting to a T fill port that was installed on the main pipe run just before it goes to the outside unit which is helpful. 

 

If I wanted to increase glycol concentrationI would just put neat glycol in (draining some volume off first if needed). Personally I dont worry too much about the exact concentration.

 

https://www.amazon.co.uk/VEVOR-Hydrostatic-Hydraulic-Pressure-Connector/dp/B0D2WR1DKV/ref=asc_df_B0D2WR1DKV?mcid=d93de40383603a05b3f862ea36531cbf&hvocijid=12890117336317427085-B0D2WR1DKV-&hvexpln=74&tag=googshopuk-21&linkCode=df0&hvadid=696285193871&hvpos=&hvnetw=g&hvrand=12890117336317427085&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9193769&hvtargid=pla-2281435176858&psc=1&gad_source=1

Edited yesterday at 19:42 by gmarshall

[ProDave]

2 hours ago, Potatoman said:

So if you found the glycol in your system was too low, how would you top it up?

Depressurise system.  Drain the missing quantity from a drain point.  Top up that missing quantity with pure glycol at the highest point which is one of the pipes on the UVC then re pressurise.

[dpmiller]

Another vote for a wee splash of glycol, here.

[Marvin]

22 hours ago, ProDave said:

I will be the odd one out then.  I have Glycol in my system.  I do NOT want the heating on 24/7 I prefer it off most of the night and prefer it to do most of the work in the day when the PV is likely co be contributing.

I do NOT want an anti freeze valve that will dump my water if it gets too cold.  

Glycol added at the ratio that will protect the system down to -10C

Never been a problem.  

That makes 2 of us.

Also there is a slim chance that the place freezes up, power goes down and 10 thousand ASHP's go pop at the same time and I will be the last on the repair list.

[ProDave]

Just to add, I am not sure what others use, but mine is filled with "Inhibitor / antifreeze" that contains glycol from one of the sheds, but I forget which one.

 

I had exactly the same concerns with an outside oil boiler in a rental property, when there was a power cut in the middle of a very cold spell.  On that occasion I did not know what level of frost protection was in the system, but luckily nothing froze or got damaged.

[Potatoman]

21 hours ago, ProDave said:

Depressurise system.  Drain the missing quantity from a drain point.  Top up that missing quantity with pure glycol at the highest point which is one of the pipes on the UVC then re pressurise.

Could you isolate and drain a radiator then fill with neat glycol

[Nickfromwales]

On 07/10/2025 at 09:41, ProDave said:

I will be the odd one out then.  I have Glycol in my system.  I do NOT want the heating on 24/7 I prefer it off most of the night and prefer it to do most of the work in the day when the PV is likely co be contributing.

 

I do NOT want an anti freeze valve that will dump my water if it gets too cold.  

 

Glycol added at the ratio that will protect the system down to -10C

 

Never been a problem.  

Nope.

 

I used glycol in a system I installed for a client in Oxon. Zero issues, no antifreeze valves, been running fine since 2022.

 

Would happily use again.

 

Caveat emptor, I have installed almost nothing but Stiebel Eltron since that job (only two others were Panasonic / Glycol) and S.E. designers say there's no need for Glycol in their systems.