Last set of Qs before ordering mvhr kit

[gambo]

I'm finally getting closer to my diy retrofit but (again) stuck on ordering what I need.

Assumptions: late 80s house, 4 people, 4 bedrooms, 3 toilets/bathrooms (once renovation completed), location in cold roof.

 

1) terminal vents are on the roof and the size of the pipe is adjustable. MVHR unit has spigots 125mm but it's a cheap unit and I may upgrade it in the future if needed. Shall I use 150/160 galv ducting from terminals to mvhr and reduce it at the unit? It will be 3-4m run with 2-3 90degree bends.

2) mainfolds - any particular difference between fancy looking ones like zehnder/ubbink and stainless steel from lidab/quiet-vent?

3) mainfolds - is there any reason why some of them say they are not compatible with comfotube? I'm doing pick-n-mix so am worried about something not working when I start installing it.

4) Noise Attenuation - where shall I install them and how many ideally? Only between unit and mainfold? I understand the need for one in supply but what is the benefit of having one on extract side?

 

[JohnMo]

4 bed house 125mm inlet out sounds way to small, is the unit big enough. Half arsed because it's cheap, likely to be noisy and not perform well. Have you done all the pressure drop calcs to check you actually get flow rates you need?

 

1 use insulated ducts - foam ones. Do presume drop calculation - is it ok for the unit? Everything in loft needs insulation.

2 not really, if in unheated loft you need insulated manifolds.

3 I mix and matched, as long as you use the same sizes should generally be ok.

4 between MVHR and outside world and between MVHR and manifolds. You are trying to stop noise from getting to rooms.

 

 

[gambo]

1) Any good software I could use to calculate it? MRXBOXAB-ECO2B - probably slightly too small but I got it almost for free so want to test it first before going for something expensive. Also the house is leaking (old double glazed windows and no cavity insulation).

2) Do i need specific insulated mainfolds or just insulate it myself?

[JohnMo]

If a leaky house MVHR just means more heat loss, not less. You are adding ventilation on top of everything leaking in. You would be better doing dMEV or MEV run on a humidity need only with matching inlet vents in dry rooms.

 

1. You don't need software a bit of paper and a one is fine. Find you longest duct route for supply and extract, this is the master route. You need to datasheet for each component within the master and see what the pressure drops are and add them up. Then look at the datasheet for the MVHR and see where you are on the fan curve.

 

Before doing the above you need to understand the room flow rates. 

 

You only look at the most onerous route not all of them 

 

2. Ideally insulation should be closed cell or cover with vapor barrier, so you don't get condensation issues.