Retrofit heat recovery ventilation - experienced advice needed

Bathsheba309

We are the process of updating our 1960s bungalow to make it more energy efficient. We have installed an ASHP and our plan is to install wet underfloor heating and an extra layer of insulation on outer walls. We are doing this on a room by room basis so will take a few years to get through the whole house! A problem that we have is high humidity and quite a bit of mould. We need additional ventilation but the cost and disruption of a whole house MVHR system being installed would be prohibitive. We need some kind of system that we can buy and get an electrician to fix. There are quite a few single room units on the market, but it's very difficult to find reviews and to understand whether they would be suitable for our space. We think we need one in the kitchen (8 x 9 metres), one in the lounge (6 x 12 metres) so two quite big spaces and then there are another 4 smaller rooms (av 4 x 4 m) that could probably do with a unit fitting. If you have any experience of these systems I would much appreciate your advice / recommendations.

Looby_Lou

If you are in a bungalow and the attic is available for ducting then the disruption of fitting a hrv system shouldn't be too bad.  The difficulty is when you are trying to get ducting into extensions and ground floor rooms from the attic!

rob7475

I've no experience in MVHR so can't comment on that.

Have you considered a PIV system though? Nuaire drimaster gets good reviews. They have a good technical team too - have a chat with them before buying to see if it will fix your problem - I'm pretty sure it will though.

Don't go for the version with the heater - it's really not neeeded.

saveallmymoney

I fitted an MHRV myself, inlets in 2 bathrooms upstairs and outlets in each bedroom. Dramatic difference in terms of no noisy bathroom fans and not a jot of condensation on the upstairs windows on a frosty morning.

It wasn't disruptive to fit where you have an attic above (which I think you do for every room!)

ComicGeek

Normally you would multiple the total floor area by 0.3 litres per second to get the total MVHR fan setting in trickle mode (ie what the system operates at for the majority of the time). The MVHR fan would then increase to boost mode (normally 120-130% of the trickle mode) when the bathroom or kitchen is being used. You could always approach one of the main manufacturers like Nuaire, Vent Axia, Titon etc as they would normally do a design free of charge for you as long as you can provide them with a basic floor plan and dimensions of rooms.

You can get individual room units, but a single centralised unit would work best. Given that you can install the unit and ducting in the loft space, it should be fairly simple to do. I would have done it years ago myself if I lived in a bungalow. 

Bathsheba309

Thanks for your answers. I've been looking into it - the single room ventilators are around £280 for the Kair ones, which seem to get very good reviews. To address the mould problems and air quality we would probably need 7 of those, plus fitting so probably around 3000 to sort the whole house. I've spoken to a couple of different firms who fit whole house systems, and it would be in the region of 15000 - so five times as much to get a full system fitted in the roof space. I was shocked that it was that much - the labour for fitting was only about a third of that cost.

ComicGeek

£15k quote for a centralised system with full loft access available is an absolutely joke. The maximum should be half that for a good spec unit and rigid ducting. A really good MVHR unit is about £1500, about the same for ducting/grilles, and then £3-4k for install (although with good loft access this shouldn't be the higher end as it really doesn't take too long!). What the hell are they spending £10k on materials on???

Do you have trickle vents in the bedrooms/living rooms? If so you could just install the individual fans in the kitchen and bathrooms - that's where you're trying to do with moisture at source. The Kair fans cycle between supply and extract modes, so will provide air movement through adjacent rooms as well, as long as you have trickle vents to bring in outside air.

Bendy_House

Hi 'Sheba.

You *currently* have issues with humidity and mould, but you are carrying out pretty extensive improvements to the insulation levels and heating in your 'low. Why do you think you will still have these issues once the work is finished?

UFH is great at keeping the overall temp at a nice steady level, so there will be less of the hot/cold winter malarkey you often get with, say, radiators, so a corresponding lack of condensation too. 

If your home is well insulated and not letting in water - I presume both will apply to you - then you simple should NOT suffer from mould. If you do, you ID the *cause* - eg excessive moisture production, or lack of extraction - and sort THAT.

Use extractors properly, and crack windows open to vent setting - job almost certainly jobbed.

If you STILL have some problems - tho' surely they'll be HUGELY diminished - then fit one single PIVS to gently air the whole house, a few hundred £s.

I think you should assume that most of your CURRENT problems will no longer apply once your work is done. Seems a waste to be considering fitting these systems at this stage?

Bathsheba309

Thanks for the replies. One of the issues regarding the loft in that all the insulation is above the ceiling and so the roof space is not part of the thermal envelope so the system and ducts would need insulating. Green Energy Store estimated cost of unit, ducting, installation etc would be in the region of 8K, with plan, install and commissioning on top of that. They based that on another bungalow that they had recently done, but it was 175m2 whereas this is around 250 so I guess would be more still, so In an ideal world we'd have a central ventilation system but I think we might have to settle for single room. There are no trickle vents fitted to the windows here and there is a lack of opening windows. We have lots of very big windows, some of which incorporate patio doors. Five rooms have no opening windows at all so the only source of ventilation is an exterior patio door. It will be years before we replace the windows and they will continue to be attractants to condensation even after we've sorted insulation and in the meantime the air quality is poor and mould is rife... I might start with three of the single room ventilators and see how noisy they are before I risk putting them into bedrooms.

Bendy_House

I understand where you're coming from, 'Sheba. But still...

That is a hell of a lot of outlay, in order to treat symptoms and not the cause. It just seems 'wrong' to me, when natural ventilation should be the obvious way to tackle it - and there MUST be ways of doing this; trickle vents should be able to be retro-fitted to windows.

And whatever is causing this excessive humidity should be tackled. If this is simply lack of ventilation, this really should be sorted - naturally. Crazy to go 'forced', when passive should do the trick. Cost = zero.

Bendy_House

And, if needed, a single, central PIVS is all most folk need to fit - the gentle positive air pressure travels throughout the house, and does its business in each room.