This is my first time posting on here but I thought a £5 fee to post a question is a good investment considering I may be spending upwards of £3000 on a MHRV system. So please be gentle …

The facts:
1. House is a roomy 1965 4 bed detached with GCH, CWI, double glazing and an open fire place (intend to block it up).
2. Four occupants, two of whom are teenagers who love the shower, one off to uni.
3. The kitchen has a very good extractor hood, but the bathroom hasn’t. We open the window.
4. We have a condensation and mould problem.
5. Bedrooms are smelly and stale in the mornings.
6. Wife gets hayfever and kids have respiratory ailments which may be caused or exacerbated by mould spores and stale air.
7. I used to work as a kitchen and bathroom installer so although unqualified, am proficient, know my house and willing to do it myself.

A simple humidistat controlled bathroom extractor seems the obvious answer but I’m tempted by a MHRV system. The heat recovery feature appeals to my environmental sensibilities, and solves the stale air issue and just makes a lot of sense. But after reading this forum these systems seem fraught with complexity and it’s thousands rather than hundreds of ££ and I have a few questions that google has been unable to answer. (I’m unwilling to ask manufacturers as I think they will tell me it’s all wonderful.) So I’d like some real world answers to the following questions:

1. Is it cost efficient for the mild UK Midlands climate? I’ve read they’re better suited to climatic extremes.
2. How does it integrate with existing cooker hood?
3. Is there a manual override or auto sensor to cope with large amounts of steam from cooking and showering? If so will input rooms get an unwanted blast of fresh air at the same time?
4. Is it ok to turn it off during summer days? We’re human, it’s nice to leave doors open in the summer, or on mild days to let the dog in and out. But would be good to switch it back on overnight. I will probably forget to do this.
5. Could redundant chimney flues be used as part of the ducting system? One TO open fireplace in living room and one FROM an old back boiler now positioned above fridge freezer.
6. Is it possible to have a system designed professionally, but install it myself?
7. Is the design and install restricted/controlled by building regs?
8. Can you have washable rather than replacement filters?
9. Are there conditions in which it is ok to turn it off or have timer settings for when the house is unoccupied during the day, or for holidays?

I suppose I’m asking how clever are these systems? Apologies for the long post, but I’m a firm believer that systems should be designed for fallible, contrary and forgetful humans with diverse requirements, not a one-size fits all for perfectionist engineers, so I’m just trying to cover all my bases!

Have a look at Ventive of You're going to block your chimney up anyway. Might make the job easier and solve your damp problem.

My view is go for it, it will sort condensation and respiratory problems nice, buy good inlet filters and change them regularly.

Sounds to like you could diy install it too.

Hi Dickie
We have a similar situation - 4 bed 1963 house, 4 people, 2 of them kids. GCH + DG + an open chimney originally.
We did an airtightness test, then fixed the worst of the leaks, then fitted MVHR maybe 3 or 4 years ago. All diy. It's not hard tbh, and you know your house better than a pro does.

We had originally intended turning it off for summer - but we don't because:
"only" 13W mean power consumption
it keeps flies out of the house
less bother than opening & closing stuff all the time

We don't integrate with existing stuff in the house - just extract from the kitchen & bathroom, input to lounge & 2 bedrooms. We have an existing kitchen extractor, that gets used rarely. I retro-fitted a flap valve to it for air tightness.

The filters *can* be washed - but our inlet one is always grubby & never as clean as new. I cut out a new one from a roll I bought, and swap the material over every time.

I definitely recommend getting one with a humidity sensor built in, and preferably with CO2 too. These will allow the unit to boost after a shower/cooking/drying clothes indoors/extra people (we have no clothes drier, but stuff dries fine with MVHR). We have a vent axia sentinel plus BH(H=humidity), with add on CO2 sensor.

While you could use a chimney, I'd be cautious unless designed for it somehow. Most units expect inlet & exhaust to be around 2m apart facing the same way, so there's no pressure difference. The last thing you want is the airflow to be dependant on how windy it is.

If you intend fitting it in your loft, make sure it will go through the hatch!

We went for oversize pipes (150mm and 200mm diameter), which keeps the air speed low, and makes it very quiet.

Back end fetch failed 503.

What an annoying website this can be.

edit: I'd just typed some useful info [I thought]!

Get some sensible forum software?

More great advice thanks! I had thought of the chimney flue as an existing duct from the loft to the living room. Of course I would have to break into the chimney breast in the loft somehow (and then connect to the MHRV unit), not an easy or particularly sensible idea! Just trying to think of routes to get the ducting downstairs without ugly boxing-in ducts in the corner of a bedroom. Maybe down through the upstairs airing-cupboard? Bit of extra free heating too?

The ventive heat exchanger is actually inside the chimney, but more useful with older style properties with open fireplaces in the bedrooms as well as downstairs.

RobL sounds like your situation is very similar to ours. Could you give me an idea of cost?

SteamyTea the obvious leaks are going to be the fireplace, toilet overflow pipes, pantry air brick - oh yes and the massive hole the cavity wall insulation installer insisting on cutting in the living room wall because of the presence of an open fire place! (oh the irony) Otherwise only a pressure test will tell me for sure.

I've got a surveyor from Envirovent coming on Thurs 14th. I'll let you know the result.

Brilliant thanks RobL. Gonna take a while reading all 152 posts on your previous thread, but very entertaining so far.

I've experienced the same; they love pushing PIV over MVHR. I guess it's an easier sale.

What Simon said. I'd add that the other thing to be a bit careful about with supply vents is to make sure they don't blow air directly at people sitting down. To a large extent that's a question of using the correct type of terminal.