MVHR installers or alternatives?

[Eastfield]

12 hours ago, G and J said:

I’m not sure I agree that it’s impossible to calculate a payback for the cost of MVHR because using Jeremy’s spreadsheet our heating requirement is a lot less than half of what it would be with sub one air changes per hour compared to say five air changes per hour that you’d need with a non-heat recovery system.

 

However, the extra spend to get airtight would be quite difficult to calculate and indeed we’ve not done a cost benefit calculation in payback terms, we’ve gone for it just as an act of faith for comfort.  So despite it being theoretically possible, I think calculating payback for MVHR for us at least is rather pointless. 

Excuse my ignorance, but why do you need such a higher number of changes per hour with a non-heat recovery system?

[G and J]

I think you need a certain number of air changes per hour to keep all fresh.  
 

With trickle vents it’s a blow through.  But with MVHR one still (as I understand it) get a good flow through if fresh air.  
 

It at first appears confusing that we have a really low air change score to make MVHR worth having, but that’s a test of the leakiness of the house, not the number of air changes that a good ventilation system will give. 

[Bonner]

10 hours ago, Eastfield said:

I'm intrigued by your sub £2k system Bonner. Are you willing to share some details? Also, I couldn't agree more re trickle vents, and I do want to have full control of my ventilation.

 

I don't want to compromise on health and comfort, ventilation is not optional. The point Jeremy is making, if I understand correctly, is that the heat saved by the MVHR is not substantial, and it would be more efficient to remove the stale air along with its heat, bring fresh air into the house and heat it via an economical heating method, which I believe I have in the biomass boiler.

Please see another post here, note the unit was 20% cheaper when I bought it. I agree the heat saving is not huge, however you would still need the fan(s), distribution system and method of preheating the incoming air to avoid cold drafts.

 

[JohnMo]

10 hours ago, Eastfield said:

Excuse my ignorance, but why do you need such a higher number of changes per hour with a non-heat recovery system?

You don't but the high number is an instantaneous air flow rate for intermittent fans. Or maybe a house leakage rate at 50Pa, which isn't the actual air movement through a building.

 

You can have good controlled ventilation without MVHR. MVHR is the icing on the cake, when you have done, wall, floor and roof insulation to death, triple glazed and made house airtight. Most houses don't need it, don't benefit from it. But they do benefit from a well thought out and appropriate ventilation system.