Whole House Ventilation with Heat Recovery

[Jason]

I'm thinking of putting this in for a Victorian house, in conjunction with some new uPVC windows to seal up the house from the cold North winds.

The attic has access to every room in the house (via vertical channels running down the sides of the chimney breats) so moving the air around should be easy enough.

So - where to start? No suppliers seem to be able to provide any decent information. They usually say "tell us what you want, and we will give you a quote". I say "tell me what you have, and I will work out my own". In this economic environment, I don't know why they are all making it so hard for me to work out what I need.

Anyway - any suggestions on where I can find information on how to plan one of these things? There are plenty of units on eBay (search for "heat recovery") starting at £400, but I have no idea if any of them are any good.

Like any DIYer, I just want to be knowledgeable enough to know what I am looking for, and make the right decisions. I suspect my total costs (for DIY) would come to around £1500. Would that be reasonable?

What I'm trying to solve is condensation and mould problems in a large Victorian end-terrace house, while at the same time keep as much heat as I can in the house.

Any tips - direct experience or otherwise - gratefully received.

-- Jason

[Tim S]

Jason coughed up some electrons that declared:

I've come across good information, including tech sheets and installation manuals for some units. Took a fair bit of googling though. I'll see if I can retrace any of the units I found - but won't be till tomorrow evening.

I do remember noting that efficiency and cost varied wildly, with the expected relationship. I did also note that single heat recovery extractor fans seemed to claim quite high efficiencies and are more like 200 quid a pop, but you need a 6" hole thorugh the wall for those.

Cheers

Tim

[Jason]

Thanks Tim. I've seen the single-room units, and they do look good. They are costly and do only cover one room (but that may be all the house needs). Again, any personal experience on these would be very handy - are the effective? Noisy? Should I avoid the units with the 12V fans (knowing how quickly 12V computer fans last, before the bearings get very noisy).

-- Jason

[Colin Wilson]

Funnily enough, I was mooching around online for these earlier today -=20 Villavent sell kits, but you're taking =A3sodding.expensive

[meow2222]

If you want to extract damp you'd be better off wth a dehumidifier. A fraction the price, fraction the run cost, more controllable, and doesnt throw 20% of your heat away.

However a better aproach is to sort out the cause of the damp first.

[BruceB]

When I was designing a system for my old mill conversion I found there was lots of useful inforomation on the vent axia site. You should be able to get it from here

[Doctor Drivel]

The average British house leaks air like hell. 42% of all heat loss is via air leakages. Putting one of these in will only vent the place twice, unless you seal the house up. That includes a sealed loft hatch and all cable and pipe entries into the loft too. If it has wooden floors then these need sealing up too.

Forget the MHRV and concentrate on air leaks and insulation. Under the floors insulate, over 1 foot in the loft. If you can get the insulation up and air leakages down you could use a MHRV as the heating system.

On exposed end gable try this:

and Kingspan do similar if not better products.

Also put proper extract ventilation over hobs and in bathrooms too. These cause condensation.

Concentrate on the matter in hand and solve at the core.

[Jason]

home. My options would be to either swap the damp internal air with less damp external air (throwing out heat with it - either all the heat, or 20% of the heat) or dehumidifying the air without exchanging it with outside air.

The former just seems healthier to me - fresh sea air in the house all the time.

-- Jason

[Jason]

Yes, totally agreed. That is one of the problems that I am trying to solve. When the wind blows from the North, it comes in around the front window frames and rotten bedroom windows. When it blows from the South it comes in under the floor. My intention is to seal all these up so that I have control over the air flow.

Sure, but once the house is sealed, that is when the condensation problems get worse. I'm aiming to tackle both problems at the same time.

that go on the inside or the outside? Inside is difficult without covering or damaging the cornicing, though would be much easier than trying to cover the outside wall. Covering the outside would not involve any internal decoration through.

It's worth me looking into though.

Totally agreed. I would just like to plan ahead for the fire I jump into after leaving the frying pan :-)

-- Jason

[Jon Fairbairn]

The Vent Axia Lo-Watt ones had the lowest power consumption last time I looked -- 14W on low.

[Jason]

Thank you. That is the single most useful set of guides on the subject yet. Not sure why I have not come across that before.

-- Jason

[Jason]

Ventaxia seem to be *the* suppliers of these things, don't they? At least, they are the only people who seem to provide a lot of useful background and technical details to consumers and DIYers.

Other suppliers I have e-mailed have come back with excuses such as "we have over 70 such products so there is no way we can keep the website up-to-date with that much information". Well, the news to that company, and many like them, is that people are making purchasing decisions while the company sleeps.

-- Jason

[Doctor Drivel]

As I have said, extract the bathroom and kitchen at source - these are the prime points that cause condensation. Auto humidity controlled extract fans can help in bathrooms too. Also eliminate the cold spots where the moist air meets a cold surface - wall insulation can do this.

Adding more insulation also reduces your fuel bills too and adds to higher comfort conditions.

Read my other post on this. Also are you doing a full renovation? Are you trying to just eliminate the condensation?

If you are doing a full renovation then make the house air tight, heavily insulate and install the MHRV with maybe an in-line heater battery to heat the house too. Use the ducting.

Off the shelf MHRV units are generally quite naff - an expensive con most of the time. All in one box and take home and fir and all is solved. Yep sure it is. To do it properly you need decent control and use the unit as heat distribution too, eliminating rads. A high flow combi can do your DHW and also heat an in-line copper heater battery, or a number of them, say one behindthe L/room grill, one for the hall, etc. Then individual control for each room. They could all be in the loft and ductwork to each room(s), if space permits.

I am not sure what you really are trying to do or solve.

[Jason]

I'm looking at the single-room extractors (with heat recovery) for the bathroom and kitchen. If I can find one at a decent price (I missed a brand new Ventaxia unit on eBay a few weeks ago that went for £120) I'll try it out and maybe - just maybe - that is all I will need (plus more insulation naturally).

Yep, that is being done too. I need to clean out 17 years of rubbish from the loft to make room for more insulation. Also sealing floorboards and insulating them from underneath (I have a three-foot gap and can get to all the floors under the building).

It's not a full renovation, so there are some limits on what I am able to do, at least in the short term.

That certainly sounds like the ideal solution, but probably too big a change seeing as this is not a complete renovation.

Increase the comfort factor, reduce draughts, increase air quality and save energy.

-- Jason

[Doctor Drivel]

> Does that go on the inside or the outside? Inside is difficult without > covering

The floors require insulation under - big job, and sealing. This will require thin boarding and sealant where floor meets walls. Air will get in and out everywhere. The loft as I have previously explained.

An end terrace is difficult to externally insulate. A detached house is easier and foam insulation can be applied and rendered over. External studs can be fitted with insulation under and between and wooden cladding over - this transforms the house too and is a wonderful make over. Could double the price. As an end terrace you have no option but to insulate internally - big job. If the rooms are big, you could put foam insulation directly on the walls. and foil lined boarding (vapour layer) over. Then the cold spots are eliminated and the heating bills go down.

Realistically you will not make the house air-tight with wooden floors, you can only make it acceptable. Insulate the walls and floors and extract the moisture at source - kitchen hob and bathroom. Have the bathroom fan come on automatically while people are in there. An extractor over the shower too. You may want to install a separate humidistat and have this bring in the bathroom fans if the level is too high. Same in the kitchen. I had a neighbour who never once turned on the kitchen extractor and the house also stunk of stale food most of the time. An auto humidistat would have brought the extractor on.

[Doctor Drivel]

Insulation and air-tightness.

Air-tightness

You need trickle vents in the new glazing. The air extract fans will pull air through these. If you have chimney breasts they are also an outside vent. Best block these up. If the breasts is internal if doesn't need an air vent in it. If on an external wall you will.

Insulation and a decent heating system with good control.

Do all the above and the condensation will disappear.

I would not install a MHRV system unless a "full well thought out" renovation is done, where the system is an integrated part of the house: heat recovery, heating, fresh air.

[BruceB]

A pleasure. I contacted x3 companies to get quotes: Vent Axia, Villavent and Regavent. Vent-Axia passed the lead onto ADM Systems and they were the only ones to come out on the ground to see the difficulties of installing in a large old mill. I ended up designing and installing my own based on their ideas, buying an Air Minder and Vent Axia accesories through ADM systems and buying the pipework through Regavent (I liked their flexible stretchy aluminium pipes and they kept the discount the same although I did not buy one of their HRV units). I needed a big unit and I wanted DC motors for economy.

Regards Bruce

[meow2222]

If you know that those are the only sources of the problem, then that sounds right to me

It is for modern houses, but old places leak like sieves and simply dont need it.

NT

[meow2222]

NT

[Doctor Drivel]

Thank you for your solid contribution.