A problem or not a problem?

[MikeGrahamT21]

Hi

 

This has been bugging me for a while, but I’m still not sure if anything is wrong as I’ve nothing really to compare it to, but one thing stands out as odd, and defying physics.

 

So MVHR system has been in around 4 years now, set the valves up last year. Unit is a Vortice HR200BP serving a small 79m2 bungalow, with all of the radial ducting in the loft under heaps of insulation. The inlet and exhaust ducts are preformed polystyrene type with a small amount of flexible ducting where needed, so as to create as little pressure drop as possible, and there is also a Blauberg Cleanbox 125 on the inlet, with G4, H16 and Carbon filtration in there.

 

Couple of years back i bought some cheap temperature sensors off amazon just out of curiousity, as although the unit has its own temperature readings, they don’t include the temperature going back into the property, only extract, inlet and exhaust.

 

Now I’m sure for a long time everything seemed feasible temperature wise, the extract was around the temperature of the bungalow, and the supply was slightly lower as you’d expect, some small losses.

 

 

Now it’s constantly higher than the extract, which is obviously not possible, there is no magic heater or anything in the ducting. You’re probably thinking, just cheap sensors that aren’t reading right, i thought so too, so i swapped the supply and extract ones round and the ‘bad’ reading followed (and yes I relocated them on the wall correctly too! lol).

 

Yesterday I had the unit all apart and checked everything, cleaned the G3 filter which is has on its extract side, and washed the heat exchanger out (though to be honest, aside from dust on the filter, it all looks like brand new in there), and it this point i moved the sensor which I had on the intake, to the exhaust just to see what temperature it showed compared with the units own sensors, and I was surprised to see it showing 17C, with an outside temp of 9C currently.

 

 

Now the units own sensors shows 14C as the exhaust temp, and the sensors are literally next to each other, but could just be the poor quality sensors again?

 

My main concern is the fact the supply seems to be warmer than the extract?! The air coming out of the ceiling valves using an IR thermometer shows between 18.8 and 19.5C depending on how far the pipe run is, which seems feasible.

 

Does this all look OK compared with your units?

 

Thanks in advance!

[JohnMo]

Dodgy temperature reading to me, or you have the wrong identity assigned to each gauge?

 

So rubbish in, rubbish out. You seem to making an issue from reading from a £1 gauge.

[Nickfromwales]

Internal pre/post heater in the unit?

[MikeGrahamT21]

No heaters in situ and like I said I’ve swapped the thermometers around and the error always stays the same, yes they are defo labelled correctly, have checked a million times myself months.

 

They are only cheap thermometers agreed, so how about the readings from the unit itself, do they seem right? I’ve just nothing to compare against and this is the only MVHR I’ve ever owned.

[gravelrash]

Extremely badly balanced? more extract than incoming so very efficient heat exchange to a smaller volume?

[MikeGrahamT21]

I balanced it all last year and got both extract and supply at the same overall values, so should be fine on that front, and the fan speed is set to the same, 35% normal and 50% boost

[MikeGrahamT21]

Out of curiosity earlier I changed the fan speeds to 40% intake and 30% exhaust and it made absolutely no difference at all, temperature stayed identical on all including the controller of the MVHR, I left it that way for a good two hours as well, have put it back to how it was previously now.

 

still curious as to what other peoples MVHRs are showing temperature wise for comparison?

[Dreadnaught]

Readings for my Vigor W325 MVHR unit just now …

• From outside: 8.9º
• To outside: 11.4º
• To dwelling: 20.8º

Internal temperature is 21.5º.

[Mr Punter]

I think that the terms used can be confusing as the words internal, inlet, intake, supply, external, exhaust and extract are used, sometimes interchangeably, to label four pipes.  It can be even more confusing if these are abbreviated to Ext, Int etc.

 

Having four readings on a cool day like @Dreadnaught has posted makes it easy to see what is being measured. 

 

I doubt there is anything wrong with the MVHR unit of the OP.

 

[MikeGrahamT21]

For clarification for my unit:

 

Ext - External - Temperature of the fresh air coming into the system

Exh - Exhaust - Temperature of the stale air once it has passed through the heat exchanger

Int - Internal - Temperature of the stale air coming into the system before heat exchanger

 

My unit doesn't have a supply temperature sensor, which is why i added some of my own, but they were only cheapy

[MikeGrahamT21]

On 01/02/2026 at 16:48, gravelrash said:

Extremely badly balanced? more extract than incoming so very efficient heat exchange to a smaller volume?

I think you were right!

 

Revisited this today. When i originally balanced it using the loan anemometer, was middle of summer, super dry and I’d just installed brand new filters into the Cleanbox which clearly had a much lower pressure drop compared to middle of winter when they’ll be holding a bit of moisture too. The figures i put up above i got wrong, they were 35% extract and 36% intake at normal speed.

 

Got the specs up of both units and ran it all through Gemini which gave me figures of 42% intake with 35% extract at normal speed, and 59% intake with 50% extract at boost to compensate for the pressure drop. I’ve knocked a couple of % off of the normal extract speed in order to get the intake down to 39%, which suited the extract being at 32% apparently.

 

I suppose this would be where a constant volume unit would come in handy which would sort itself out.

 

So yeah, thanks for seeding the idea, I’ll keep an eye on temps etc and see if that cures it, I clearly didn’t leave it long enough the other day when i was messing

Edited February 3 by MikeGrahamT21

[MikeGrahamT21]

So after around a week with the new fan speeds, it’s got the exhaust value down a couple of degrees without changing the supply temperature so that’s good, but the supply is still warmer than the extract.

 

decided to get the thermal camera on it and it gives a similar reading

 

extract pipe

 

supply pipe

 

observe the centre value as this was pointed at the plastic PVC pipe which is same on both and not reflective