Moisture control

[Stinsy]

We shouldn't be ashamed! Everything you do has side effects, admitting them and mitigating them is part of the process.

MHRV is a very important part of modern air-tight, well-insulated, homes. When we retrofit insulation/draught-proofing to our homes we must also acknowledge and deal with damp. It is a shame that dehumidifiers consume energy, but they also generate heat that we make use of...

[Joeboy]

We shouldn't be ashamed! Everything you do has side effects, admitting them and mitigating them is part of the process.

MHRV is a very important part of modern air-tight, well-insulated, homes. When we retrofit insulation/draught-proofing to our homes we must also acknowledge and deal with damp. It is a shame that dehumidifiers consume energy, but they also generate heat that we make use of...

I think we'll all be interested to hear your consumption figures when you are up and running? We are now seeing quite a slowdown on water so will move tomorow.

[Stinsy]

I think the fact I haven't got the heating on yet is playing a part. However I would be interested in a mini MHRV system if anyone knows of something I could DIY fit?

[Bugtownboy]

As per previous in this thread, Stinsy. We run a single room MVHR (VentAxia, others are available) in the main bathroom (upstairs). Consumes when running continuously, from memory, 2-3w/hr.

I’ve never taken humidity readings, but the humidistat (can’t find the setting) kicks in when we shower or take a bath to damp up air-change.

OK, may not be the most efficient at heat exchanger, think they reckon 70%+, but from a comfort perspective it appears to work - does for us anyway.

As well as this we also run a WBS throughout the day, so a degree of air change there.

As per previous post, also use an externally vented cooker hood when cooking and don’t dry clothes inside. Second bathroom has an effective vent - only operational when second bathroom in use.

[marshman]

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[Joeboy]

I first fitted a MHRV system in my previous house around 20 years ago. At that time I got Rega Ductex to "design" the system and supply all the bits but I fitted it. That way I could ensure all the ducting was hidden as I knew the construction of the house and was prepared to spend time feeding ducting between floors and in studding walls etc. System worked really well and condensation was never a problem.

I "DIY" retrofitted MHRV in my current house 5 years ago just after I had the heat pump installed. I knew I was going to get the old draughty wooden windows replaced and was "on a mission" to stop any draughts and also go over board with insulation so knew ventilation was mega important. I was so impressed with the previous install that it was a "no brainer". I saw a Rega Ductex fan unit for sale on eBay, it was mis-described so I got it really cheap. This time I planned the duct runs myself and bought all the bits from "fans 4 less" - ducting, connectors, filters, acoustic dampers, fire dampers, room outlets, tape etc. Total "component" cost was around £500 plus the fan unit. Took a couple of weekends to install all the ducting and I took a lot of trouble to make sure it was all hidden. This did involve quite a lot of work core drilling through walls, pulling up floor boards etc. (it is a very old brick built farmhouse) but i was pleased with the result - no visible ducting, virtually silent in trickle mode. Works really well, never, and I mean never any condensation anywhere - except in the bathroom after someone takes a really hot shower, but the room, windows and mirrors are clear in less than 5 minutes. House always feels fresh, I leave it running 24/7, gets "boosted" when cooking but not when showering, no need. fans come around 50W when in trickle mode, 200W flat out.

I have also retro-fitted two smaller systems to small single story dwellings, one used a Vent Axia fan unit - now quite expensive and the other a cheaper fan unit I found on eBay. To be honest there doesn't seem to be much difference between the two other than the eBay one was a third of the price.

I did read up a lot on it before my first install and I read a lot about the pros and cons of rigid or flexible ducting, efficiency of heat exchangers, humidistats and allsorts of "clever" controls. My opinion is that as long as you plan the duct runs sensibly and try to achieve a balanced system then any advantage of rigid (smooth) ducting, or any of the other things is very small. Not sure what the efficiency of my heat exchanger is but at the moment it is 6.9 deg C out side and the in-coming air is currently 17 deg C. The humidity is a steady 55%.

To me MHRV goes hand in hand with draught proofing and insulation - you need to look at the whole package, condensation and damp is not good for a building or its occupants and to me dehumidifiers are a sticking plaster solution which cure the symptoms rather than the cause.

Roger

Hi Roger,
Nice amount of detail in there. Any chance of a photo or two of the main unit and room outlets? I'll likely be dehumidifiers for a while yet but I never say never. More info in my brain the better. Cheers!

[Stinsy]

I first fitted a MHRV system in my previous house around 20 years ago. At that time I got Rega Ductex to "design" the system and supply all the bits but I fitted it. That way I could ensure all the ducting was hidden as I knew the construction of the house and was prepared to spend time feeding ducting between floors and in studding walls etc. System worked really well and condensation was never a problem.

I "DIY" retrofitted MHRV in my current house 5 years ago just after I had the heat pump installed. I knew I was going to get the old draughty wooden windows replaced and was "on a mission" to stop any draughts and also go over board with insulation so knew ventilation was mega important. I was so impressed with the previous install that it was a "no brainer". I saw a Rega Ductex fan unit for sale on eBay, it was mis-described so I got it really cheap. This time I planned the duct runs myself and bought all the bits from "fans 4 less" - ducting, connectors, filters, acoustic dampers, fire dampers, room outlets, tape etc. Total "component" cost was around £500 plus the fan unit. Took a couple of weekends to install all the ducting and I took a lot of trouble to make sure it was all hidden. This did involve quite a lot of work core drilling through walls, pulling up floor boards etc. (it is a very old brick built farmhouse) but i was pleased with the result - no visible ducting, virtually silent in trickle mode. Works really well, never, and I mean never any condensation anywhere - except in the bathroom after someone takes a really hot shower, but the room, windows and mirrors are clear in less than 5 minutes. House always feels fresh, I leave it running 24/7, gets "boosted" when cooking but not when showering, no need. fans come around 50W when in trickle mode, 200W flat out.

I have also retro-fitted two smaller systems to small single story dwellings, one used a Vent Axia fan unit - now quite expensive and the other a cheaper fan unit I found on eBay. To be honest there doesn't seem to be much difference between the two other than the eBay one was a third of the price.

I did read up a lot on it before my first install and I read a lot about the pros and cons of rigid or flexible ducting, efficiency of heat exchangers, humidistats and allsorts of "clever" controls. My opinion is that as long as you plan the duct runs sensibly and try to achieve a balanced system then any advantage of rigid (smooth) ducting, or any of the other things is very small. Not sure what the efficiency of my heat exchanger is but at the moment it is 6.9 deg C out side and the in-coming air is currently 17 deg C. The humidity is a steady 55%.

To me MHRV goes hand in hand with draught proofing and insulation - you need to look at the whole package, condensation and damp is not good for a building or its occupants and to me dehumidifiers are a sticking plaster solution which cure the symptoms rather than the cause.

Roger

Hi Roger, thanks for the detail. I’m interested in installing a very simple system next year. Extract from bathroom and en-suite, return in hallway, all ducting in the attic. I don’t want to spend thousands.

Is this a good plan?
What will I need?

Help is appreciated!

[Countrypaul]

Like Roger, I got a MVHR system which was designed but the supplier (Airflow) but a DIY install. I installed the ducting whilst we were still renovating which allowed me easy access as we had no ceilings but do have open webbed joists, and we had the studs for the walls in place upstairs but no plasterboard or insulation in place. We used the semi flexible ducting all starting in the utility room where we have the 2 plenums that take the 180mm feeds to/from the main unit to the various separate ducts to/from the rooms. I did have to core drill some solid walls as the orginal design had the ducts going through glulam support beams or in one case a steel beam (205x205x80) and in each case we were looking at 6 ducts passing through. The main intake/exhaust ducts do swap between round and rectangular to pass through the joists and also have 4 x 45 degree bends in each as getting to the outside walls proved move difficult than initialy expected (but the 45 bends dont make 90 anywhere). The main unit is fitted on the wall (not easy as it weighed nearly 90Kg) when doing it alone but we cannot detect any vibration or noise outside the utility room other than through the vents when as a high setting.

We normally have the unit set on the minimum level but during spring summer when we had no heating on but the kids were at home due to Covid we tended to run at a higher level 3-4 (the unit supports 8 levels). If cooking with a high level of steam or someone taking a long hot shower we will hit the boost button which sets the unit to level 8 for 45 minutes. We have had no problems with mould anywhere and the place always seems fresh. Even when cooking things sucha s curries, smoked fish etc. that tends to create a lingering smell this clears fairly quickly.

Only regret, we have no heating in the bedrooms, unforunately that can result in themcooling down significantly and complaints from the rest of the family who seem to want a warm bedroom. Looking at it in a simplistic way, the unit claims upto 90% efficient, being realistic I assume 80%, as such if it is 0C outside and 20C inside the supply air to the bedrooms is only 16C. I should have fitted a duct heater running off the CH system, and this is something I am considering. The correct duct heater could also be used as a duct cooler during summer which would also be helpful.

As Roger says, don't look at the MVHR system alone, it only makes sense if the place is well sealed and well insulated. In our previous place we used a dehumidifier but still suffered from damp and mould problems - however that was an ex-farm cottage with solid 9" walls and leaked air like a sieve.

One aspect that is easily overlooked is that you also need to allow airflow through the room doors so that generally means a gap beneath the door to let the air out of those it is suplied to and in to those it is extracted from. Extraction is normally from bathrooms, WC, Kitchen, Utility and supply to reception rooms and bedrooms we have no extraction or supply to the hallway/landing as there is flow through these from the rooms air is supplied to going to those it is extracted from.

[Joeboy]

We shouldn't be ashamed! Everything you do has side effects, admitting them and mitigating them is part of the process.

MHRV is a very important part of modern air-tight, well-insulated, homes. When we retrofit insulation/draught-proofing to our homes we must also acknowledge and deal with damp. It is a shame that dehumidifiers consume energy, but they also generate heat that we make use of...

How are you getting on with your dehumidifier? Our two are continuing to pull volumes of water. Thought they'd have tailed off by now. Nope, still pulling a gallon+ between them per day.

[Bugtownboy]

You still keeping that gallon kettle going all day Joe