Anybody know about MVHR?
Discussion
I’m looking at installing as part of an extension project as it gives me a chance to install the ducts.
we have a large room with a woodburner that we tend to use in the evenings and if it’s not quite cold enough to fire up the heating, I’m wondering whether we could use the vent system to circulate heat around the rest of the house by putting extract into this room rather than supply.
Does this sound like a stupid idea?
we have a large room with a woodburner that we tend to use in the evenings and if it’s not quite cold enough to fire up the heating, I’m wondering whether we could use the vent system to circulate heat around the rest of the house by putting extract into this room rather than supply.
Does this sound like a stupid idea?
A room with a woodburner will need an air supply, although you can get 'room sealed' wood burners which have a separate air supply.
Extracting air from this room would draw air down the flue making the fire hard to light and potentially causing carbon monoxide issues and smell when the fire isn't lit.
I'd suspect that the chimney draw might lower the pressure in the room enough to make the MVHR fan work hard and use a lot of electricity?
It seems quite hard to get solid data on how much power these things will use in various 'real life' situations.
I have been looking at this for a house I might buy. The main thing would be to extract damp air from the shower rooms and kitchen. Recovering the heat is a good idea when it's cold, but here in Devon, problem time for ventilation is like this month, when it's been continually wet but not very cold.
A mate is looking at changing to a wood burner which also heats water for radiators and HW cylinder.
I'm back to just kicking ideas around at this point, but might also be interested in some kind of whole house ventilation scheme with aircon for the summer.
Big problem with MVHR is that the equipment is very expensive, particularly in the UK it seems, and more so when you have free firewood.
Plus of course, ducting air to/from downstairs rooms is a sod to retrofit!
Interested in other people's views and experiences, there have been a few threads on here touching on these subjects.
Extracting air from this room would draw air down the flue making the fire hard to light and potentially causing carbon monoxide issues and smell when the fire isn't lit.
I'd suspect that the chimney draw might lower the pressure in the room enough to make the MVHR fan work hard and use a lot of electricity?
It seems quite hard to get solid data on how much power these things will use in various 'real life' situations.
I have been looking at this for a house I might buy. The main thing would be to extract damp air from the shower rooms and kitchen. Recovering the heat is a good idea when it's cold, but here in Devon, problem time for ventilation is like this month, when it's been continually wet but not very cold.
A mate is looking at changing to a wood burner which also heats water for radiators and HW cylinder.
I'm back to just kicking ideas around at this point, but might also be interested in some kind of whole house ventilation scheme with aircon for the summer.
Big problem with MVHR is that the equipment is very expensive, particularly in the UK it seems, and more so when you have free firewood.
Plus of course, ducting air to/from downstairs rooms is a sod to retrofit!
Interested in other people's views and experiences, there have been a few threads on here touching on these subjects.
Yup, we have recently had an MVHR installed in our house during a complete renovation.
Yes if you have one hot room with a fire, then if that room has extracts in it, then it will circulate the heat into the rest of the house in an indirect manner.
All inlet ducts join into one huge inlet via a manifold and vice versa on the outlets, so all air in and all air out is combined at the heat exchanger.
We have a 10kw DRU gas tunnel fire in the kitchen-dining-living space, and have precisely this idea in mind for the coldest of weeks in winter. The living room side has 3 outlets and the kitchen side has 3 inlets. As you say though only inlets are needed in the room with the fire/burner for the idea to work.
The chimney point didnt apply to us, we had a balanced flue run into the old chimney for the DRU gas fireplace. Maybe with a real open fire it might cause a little bit of an issue - just check with the MVHR supplier first, Im sure they will know how to deal with it as many houses have chimneys.
Yes if you have one hot room with a fire, then if that room has extracts in it, then it will circulate the heat into the rest of the house in an indirect manner.
All inlet ducts join into one huge inlet via a manifold and vice versa on the outlets, so all air in and all air out is combined at the heat exchanger.
We have a 10kw DRU gas tunnel fire in the kitchen-dining-living space, and have precisely this idea in mind for the coldest of weeks in winter. The living room side has 3 outlets and the kitchen side has 3 inlets. As you say though only inlets are needed in the room with the fire/burner for the idea to work.
The chimney point didnt apply to us, we had a balanced flue run into the old chimney for the DRU gas fireplace. Maybe with a real open fire it might cause a little bit of an issue - just check with the MVHR supplier first, Im sure they will know how to deal with it as many houses have chimneys.
Edited by AdamV12V on Saturday 20th September 22:25
OutInTheShed said:
Big problem with MVHR is that the equipment is very expensive, particularly in the UK it seems, and more so when you have free firewood.
Plus of course, ducting air to/from downstairs rooms is a sod to retrofit!
Its all relative...Plus of course, ducting air to/from downstairs rooms is a sod to retrofit!
In the cost of our refurb the MVHR (a Zhender Q600ST) and install was around 1% of the total spend.
IMHO its probably the best 1% we've spent on anything during the project!
Ducting would have been tricky for a partial refurb but in our case we were pulling down all the ceilings and redoing them, so at that point running some ducts and plastering in inlets/outlets was a modestly small job.
PS: Go for plaster-in vents (almost invisible) if you can - only cost a tiny bit more each and look a million times nicer than the default steel vents.
Edited by AdamV12V on Saturday 20th September 21:24
caziques said:
You would need an air to air heat exchanger and two fans, plus ducting of course.
A well designed system would circulate warm air around. Just remember wafting warm air around at ceiling level isn't a good way of heating a room.
The heat exchanger and fans are commonly, but not always, built into a single unit.A well designed system would circulate warm air around. Just remember wafting warm air around at ceiling level isn't a good way of heating a room.
The object of the game is not really heating rooms, as the air blown into a room is always going to be cooler than the air extracted from another room.
It just means you're getting fresh air in warmer than outdoors.
If you're extracting over a kitchen hob, then yes, the warmed fresh air could be quite warm, but mostly you're taking air at say 23 deg C from a bathroom and using it to warm outdoor air coming it at say 10 degC to maybe 18degC or something.
You still need heating, but you can have more 'air changes' without it dominating your heating bill.
Back in the 70s, I recall seeing lots of mid-range estate type houses with blown warm air central heating. A mate had one in the late 80s or maybe early 90s, and couldn't wait to install 'normal' radiators. I think blown air gas central heating is still more common on the wrong side of the Atlantic?
OutInTheShed said:
It seems quite hard to get solid data on how much power these things will use in various 'real life' situations.
Im more than happy to share the power use of ours - it is absolutely minimal. Staggeringly low given the throughput it gives.Right now its on the default setting (speed 2) and itrs using 25W to supply 45 litres/second to the half of the house which is finished.
Extracted air is 19.9C / 66% humidity
Outside air is 10.5C / 92% humidity
Supplied air is 19.2C / 56% humidity
Thats about the biggest drop ive seen at 0.7C but its a damn sight less than the obvious 8.7C difference if we just had trickle vents in the windows!
That is a valid point however - if you have trickle vents in your windows and arnt planning to replace them, then you'll need to block them up.
OutInTheShed said:
The heat exchanger and fans are commonly, but not always, built into a single unit.
The object of the game is not really heating rooms, as the air blown into a room is always going to be cooler than the air extracted from another room.
It just means you're getting fresh air in warmer than outdoors.
If you're extracting over a kitchen hob, then yes, the warmed fresh air could be quite warm, but mostly you're taking air at say 23 deg C from a bathroom and using it to warm outdoor air coming it at say 10 degC to maybe 18degC or something.
You still need heating, but you can have more 'air changes' without it dominating your heating bill.
Back in the 70s, I recall seeing lots of mid-range estate type houses with blown warm air central heating. A mate had one in the late 80s or maybe early 90s, and couldn't wait to install 'normal' radiators. I think blown air gas central heating is still more common on the wrong side of the Atlantic?
Mainly because cooling is also a requirement. Makes sense to have the same system do both. It also makes heat pump integration way simpler, which has become a very popular upgrade.The object of the game is not really heating rooms, as the air blown into a room is always going to be cooler than the air extracted from another room.
It just means you're getting fresh air in warmer than outdoors.
If you're extracting over a kitchen hob, then yes, the warmed fresh air could be quite warm, but mostly you're taking air at say 23 deg C from a bathroom and using it to warm outdoor air coming it at say 10 degC to maybe 18degC or something.
You still need heating, but you can have more 'air changes' without it dominating your heating bill.
Back in the 70s, I recall seeing lots of mid-range estate type houses with blown warm air central heating. A mate had one in the late 80s or maybe early 90s, and couldn't wait to install 'normal' radiators. I think blown air gas central heating is still more common on the wrong side of the Atlantic?
OutInTheShed said:
A mate is looking at changing to a wood burner which also heats water for radiators and HW cylinder.
A chap i know did this with a dedicated control board and ended up getting it all ripped out as it would never regulate the heat properly.This was a few years ago so i guess newer systems are better.
AdamV12V said:
Im more than happy to share the power use of ours - it is absolutely minimal. Staggeringly low given the throughput it gives.
Right now its on the default setting (speed 2) and itrs using 25W to supply 45 litres/second to the half of the house which is finished.
Extracted air is 19.9C / 66% humidity
Outside air is 10.5C / 92% humidity
Supplied air is 19.2C / 56% humidity
Thats about the biggest drop ive seen at 0.7C but its a damn sight less than the obvious 8.7C difference if we just had trickle vents in the windows!
That is a valid point however - if you have trickle vents in your windows and arnt planning to replace them, then you'll need to block them up.
Thanks, it’s that drop in RH which is one of the major benefits to us, we’re on the St Davids peninsula so sea on 2 sides and stored clothes can be a bit clammy at certain times of year, the idea of circulating heat from the woodburner was an added (silly) ideaRight now its on the default setting (speed 2) and itrs using 25W to supply 45 litres/second to the half of the house which is finished.
Extracted air is 19.9C / 66% humidity
Outside air is 10.5C / 92% humidity
Supplied air is 19.2C / 56% humidity
Thats about the biggest drop ive seen at 0.7C but its a damn sight less than the obvious 8.7C difference if we just had trickle vents in the windows!
That is a valid point however - if you have trickle vents in your windows and arnt planning to replace them, then you'll need to block them up.
Just to add I have been involved in 2 large new build houses recently with full MVHR.
I was extremely impressed that none of the windows fogged up, including some big bifold doors - you normally get really high humidity from all the plaster, cement, concrete etc whilst it dries out.
Be careful where you site the main fan/heat exchanger unit. They're not particularly noisy, but background hum could get annoying if placed too close to a bedroom...
I was extremely impressed that none of the windows fogged up, including some big bifold doors - you normally get really high humidity from all the plaster, cement, concrete etc whilst it dries out.
Be careful where you site the main fan/heat exchanger unit. They're not particularly noisy, but background hum could get annoying if placed too close to a bedroom...
Biker 1 said:
Just to add I have been involved in 2 large new build houses recently with full MVHR.
I was extremely impressed that none of the windows fogged up, including some big bifold doors - you normally get really high humidity from all the plaster, cement, concrete etc whilst it dries out.
Be careful where you site the main fan/heat exchanger unit. They're not particularly noisy, but background hum could get annoying if placed too close to a bedroom...
I've heard it said that with plaster etc, you need to allow (initially) high humidity while it's drying out, or the vapour pressure can literally blow the plaster off the walls. Quite likely the latest modern glazing is a lot more resistant to condensation than mine?I was extremely impressed that none of the windows fogged up, including some big bifold doors - you normally get really high humidity from all the plaster, cement, concrete etc whilst it dries out.
Be careful where you site the main fan/heat exchanger unit. They're not particularly noisy, but background hum could get annoying if placed too close to a bedroom...
The noise aspect does concern me. In a location with sometimes very little background noise, hum from fans and stuff combines badly with my tinnitus.
To be fair there is some hum from it which can be heard when laid in bed mostly and comes through the ducts more than anything to do with proximity to the unit itself for us, but I m sure that s a valid consideration which could make it even more apparent!
It s down to your personal perception, as my mrs doesn t notice it until I mention it. That said I can also hear the ASHP s come on which are outside and used to be able to hear the gas boiler which was at the other end of the house so I appear to be unusually sensitive to deep rumbling sounds. You can t hear it through the day or when anything like the TV is on as it s genuinely only a tiny background hum.
Ours has a schedule so it can be turned down to speed 1 or speed 0 (away mode - so bare min speed), overnight, but for the time being I don t want to risk letting humidity get the upper hand as half the house isn t renovated yet and that half is prone to condensation and obviously unfinished / finished rooms just have a door or two between them for now. For sure it s nailed any condensation in the finished rooms, one of which (the master bedroom) was the worst room in the house before.
It s down to your personal perception, as my mrs doesn t notice it until I mention it. That said I can also hear the ASHP s come on which are outside and used to be able to hear the gas boiler which was at the other end of the house so I appear to be unusually sensitive to deep rumbling sounds. You can t hear it through the day or when anything like the TV is on as it s genuinely only a tiny background hum.
Ours has a schedule so it can be turned down to speed 1 or speed 0 (away mode - so bare min speed), overnight, but for the time being I don t want to risk letting humidity get the upper hand as half the house isn t renovated yet and that half is prone to condensation and obviously unfinished / finished rooms just have a door or two between them for now. For sure it s nailed any condensation in the finished rooms, one of which (the master bedroom) was the worst room in the house before.
Edited by AdamV12V on Sunday 21st September 11:43
gareth h said:
I m looking at installing as part of an extension project as it gives me a chance to install the ducts.
we have a large room with a woodburner that we tend to use in the evenings and if it s not quite cold enough to fire up the heating, I m wondering whether we could use the vent system to circulate heat around the rest of the house by putting extract into this room rather than supply.
Does this sound like a stupid idea?
The low flow rate combined with the low heat capacity of air means that MVHR is quite an ineffective method to heat (or indeed cool) a house so I doubt it'd provide much benefit in practice.we have a large room with a woodburner that we tend to use in the evenings and if it s not quite cold enough to fire up the heating, I m wondering whether we could use the vent system to circulate heat around the rest of the house by putting extract into this room rather than supply.
Does this sound like a stupid idea?
Besides, as another poster mentioned, it is not a good idea to have an extract in the same room as a woodburner (unless it is room-sealed) and, being a living room, you'd usually be looking at putting a supply in there anyway as it will benefit from a fresh air supply. That itself might go some way towards helping move some of the warm air from the extension through to the rest of the house.
Don't let me put you off MVHR though - I'm a big fan, if you'll excuse the pun. We've had it in two properties - the first fitted when new which we were so impressed with we retrofitted it to our current house.
outnumbered said:
MVHR are fine as an efficient method of ventilation with minimal heat loss. They are not, in any way, a heating system.
To be fair that’s not what the OP said…He was asking if the excess heat from a burner in one room could be redistributed through the rest of the house via an MVHR. It will do this, although not to the extent to meaningfully heat the rest of the house but it will mean warmer air going back in as everything is averaged out when it’s combined across all inlets / outlets in the manifolds.
AdamV12V said:
outnumbered said:
MVHR are fine as an efficient method of ventilation with minimal heat loss. They are not, in any way, a heating system.
To be fair that s not what the OP said He was asking if the excess heat from a burner in one room could be redistributed through the rest of the house via an MVHR. It will do this, although not to the extent to meaningfully heat the rest of the house but it will mean warmer air going back in as everything is averaged out when it s combined across all inlets / outlets in the manifolds.
Log burner enthusiasts often have their lounge over 20degC.
Other rooms in the house, you might be happy with as little as 17degC, provided they were ventilated and humidity controlled.
A lot of people have lightly used rooms in their houses.
Some people don't want e.g. bedrooms as warm as the lounge. If you're using a room as a gym, what temperature do you need?
If you've got a really well insulated house, air changes can be the dominant heat loss.
Maybe there is a limit to how much discussion is worthwhile without getting numerical?
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