MEV or MVHR - that is the question!

bemak

I have started renovation works to an old stone farmhouse (150sqm) which involves the addition of a two-storey extension. We've decided to go down the route of UFH on both floors which will be run with a traditional oil boiler for now. We've allowed provisions for a HP in the future. The heating will be supplemented by a back boiler in a solid fuel stove.

As the existing stone walls will be rendered internally with an insulating lime render to allow moisture to escape - I want to install a good ventilation system that will help to extract moisture from the house. The preference is for the unit to go in a warm attic, from which I can duct all the rooms. As the layout of the house is quite simple, the routes are relatively straightforward. 

The question now is, which system to go for. I've narrowed it down to MEV or MVHR. As the house is being completely gutted, I think it's likely that the airtightness will be good enough for a MVHR unit and while on paper I like the benefits of a MVHR unit over a MEV unit, I'm just wondering if it's worth the extra running cost (2 fans instead of 1). My priority is to get moisture out of the house as it occurs - so a MEV system with trickle vents in the windows will likely do the job just fine - but I don't want to be sorry later for not installing MVHR.

Is it possible to set a MVHR unit to 'extract only' so that it would essentially work like a MEV if I wanted it to?

BenIrishHome

First question, why not just go Heat Pump day one? Not much more than an oil boiler.

Secondly, the running costs of MEV and MVHR are tiny, you won't notice the difference. It's more the upfront capital costs, which probably arent a huge difference. Usually retrofitting its the hassle of running the ducts, but if you think that's simple then I'd say go for it.

From what I've picked up… I am no expert. About to retrofit a 2000s dormer bungalow and apparently I would never be airtight enough for MVHR to be worth it, so I am basically being advised to go trickle vents and MEV.

bemak

how deep are you going with the retrofit? once the envelope is sealed you could do an airtightness test to see if you could get MVHR.