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Any advice on heat recovery fans from Vent Axia and how good thier "h" humidity function works?

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diy_massacre

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Hi

I have an old house which has had double glazing fitted to the rear of the property, in the kitchen, good for heat retention but not for damp. I was expecting to buy a Vent axia in-room MHVR fan to help with drying out the room and maintaining its temperature.

The model which I think continuously runs 24/7 but can also detect higher humidity so when there is alot of cooking/boiling and humidity rises it ramps up its output. Has anybody had any experience if these work well or not?

Thanks

diy_m
 

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I have fitted a Vent-Axia humidistat fan to a bathroom, though without heat recovery. From the feedback the landlady has had from the tenants, I would comment:

The fact that it monitors RH and kicks in when it detects a quick rise in RH (even if the RH is below the setpoint) is useful. Someone starts the shower and the fan kicks in within seconds.

The constant monitoring of RH is possibly less useful as the fan struggles to know when it can switch off. Issues can arise as RH is not a terribly useful thing to measure in the British climate. If the incoming air is from outside, the RH of external air coming in can sometimes be high even if the absolute humidity of that air is low. The sensor simply cannot distinguish between comparatively dry cold air at a high RH and comparatively damp warm air at the same RH.
 
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When I moved into my house we had mould behind furniture upstairs so I bought a dehumidifier which did the trick.
I found the cooker hood was on recirculate. I then ducted it to outside and the dehumidifier is now redundant.
Don't forget that for an extractor to work you need air to come in! I've worked in numerous buildings where fans were in sealed rooms. One had a 9" Ventaxia which you could hear speed up whenever the door was opened!
 
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Ric2013 said:
I have fitted a Vent-Axia humidistat fan to a bathroom, though without heat recovery. From the feedback the landlady has had from the tenants, I would comment:

The fact that it monitors RH and kicks in when it detects a quick rise in RH (even if the RH is below the setpoint) is useful. Someone starts the shower and the fan kicks in within seconds.

The constant monitoring of RH is possibly less useful as the fan struggles to know when it can switch off. Issues can arise as RH is not a terribly useful thing to measure in the British climate. If the incoming air is from outside, the RH of external air coming in can sometimes be high even if the absolute humidity of that air is low. The sensor simply cannot distinguish between comparatively dry cold air at a high RH and comparatively damp warm air at the same RH.
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Thanks Ric2013

I like your response, thats a good datapoint!

I always assumed the humidity detector would be on the internal inflow to the unit inside rather than the incoming air. But interesting so hear about the sensor not being able to distinguish.

Thanks

diy_m
 
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Dannyk said:
When I moved into my house we had mould behind furniture upstairs so I bought a dehumidifier which did the trick.
I found the cooker hood was on recirculate. I then ducted it to outside and the dehumidifier is now redundant.
Don't forget that for an extractor to work you need air to come in! I've worked in numerous buildings where fans were in sealed rooms. One had a 9" Ventaxia which you could hear speed up whenever the door was opened!
Click to expand...
Thanks, food for thought!

I could try and connect the cooker hood to the outside but he piping wouldn't look pretty and think the management may not like the outcome.

The house leaks air like a sieve with air coming in everywhere, we have ledge and brace bent doors which plug a gap but dont seal, so it can only get better.

Thanks

diy_m
 
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diy_massacre said:
Thanks Ric2013

I like your response, thats a good datapoint!

I always assumed the humidity detector would be on the internal inflow to the unit inside rather than the incoming air. But interesting so hear about the sensor not being able to distinguish.

Thanks

diy_m
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Crossed wires here. It will monitor the air inside the room. However, the air in the room will be replaced with outside air which may have a high RH. So the 'new' air in the room may also seem damp to the sensor. The fact that your fan will preheat the incoming air will certainly help it distinguish, however, the very act of heating the air will cause the RH to fall somewhat.
 
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If you're prepared to drill a hole through the outside wall for a humidity fan why is it a problem for an extractor fan?

It seems you're attracted to a particular solution that isn't even designed for kitchens and the problem you say is damp. You can get low profile ducting that can sit on top or even inside kitchen cabinets quite unobtrusively if you have tradtional fitted style kitchen. A full cooker extractor system ducted to the outside is what you need.
 
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I'd never heard of these humidity fans till seeing this thread. They seem to be a poor expensive solution looking for a problem.
Cost £300!
Extraction a mere 9l/s compared to a cooker hood's 111l/s or a 6" kitchen fan's 200+l/s (cost<£100).
gmartine is right.
I eventually sited the hob on outside wall on a refit.
 
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Been using these for the last 8 months in bathrooms, kitchen and utility room. I swapped all existing fans for them. Expensive but well worth it. My plan is to add them to all rooms and lofts as well. Ventilation is so badly neglected
 
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hometech said:
Been using these for the last 8 months in bathrooms, kitchen and utility room. I swapped all existing fans for them. Expensive but well worth it. My plan is to add them to all rooms and lofts as well. Ventilation is so badly neglected
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Why bother installing a heat recovery fan in a room where there's no high humidity/temperature to recover the heat from.
 
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gmartine said:
Why bother installing a heat recovery fan in a room where there's no high humidity/temperature to recover the heat from.
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It depends what percentage of heat is recovered and if you need constant operation. If the fan consumes 5W of electricity and is run constantly, that's 0.13kW per day.

But 9l/s is 32cu m. an hour. So you could be changing all the air in the room once per hour at that rate.

As far as I can gather (very roughly indeed), it takes around 1.2W to heat a cubic meter of air by 1°C. So at 20°C indoors and 10°C outdoors, every day would have 770 cu m x delta 10 x 1.2W = 9.2kWh. Recover half that energy and you've saved 4.5kW. Nearly a pound's worth of electricity if you're a low energy user or on a genuinely green tariff.

So, assuming the fan lasts only 3 years, and assuming a 100 day heating season it is still paying for itself compared with just opening the window. So not a stupid idea at all.
 
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Ric2013 said:
Crossed wires here. It will monitor the air inside the room. However, the air in the room will be replaced with outside air which may have a high RH. So the 'new' air in the room may also seem damp to the sensor. The fact that your fan will preheat the incoming air will certainly help it distinguish, however, the very act of heating the air will cause the RH to fall somewhat.
Click to expand...
Hi Ric2013

Yes understand your point, thanks for the clarification. Think I will get one anyway even if it overruns sometimes.

Many thanks

diy_m
 
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hometech said:
I don't expect the average person to understand so no point in discussing that with you
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Murdoch said:
Back with your condescending replies again?
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Ric2013 said:
It depends what percentage of heat is recovered and if you need constant operation. If the fan consumes 5W of electricity and is run constantly, that's 0.13kW per day.

But 9l/s is 32cu m. an hour. So you could be changing all the air in the room once per hour at that rate.

As far as I can gather (very roughly indeed), it takes around 1.2W to heat a cubic meter of air by 1°C. So at 20°C indoors and 10°C outdoors, every day would have 770 cu m x delta 10 x 1.2W = 9.2kWh. Recover half that energy and you've saved 4.5kW. Nearly a pound's worth of electricity if you're a low energy user or on a genuinely green tariff.

So, assuming the fan lasts only 3 years, and assuming a 100 day heating season it is still paying for itself compared with just opening the window. So not a stupid idea at all.
Click to expand...

I have no problem with the principle of heat recovery just the thought of using an extractor fan designed for a high humidity environment like a bathroom being used in a room that it isn't designed for. The issue is the hex's on these particular fans are usually triggered by humidistat that can be set but not at a level that is applicable for say bedrooms as is being preposed not to mention the noise emanating from them also makes them inappropriate.

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You're welcome.
 
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