Should I retain DVS when installing Ducted Heatpump

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generationy

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#319008 13-Mar-2025 11:27

2015 Home Concrete Block home with Double Glazing and DVS. Currently no condensation throughout, but gets cold in winter and a bit hot summer nights. So we want to add a ducted heat pump to our home (heat pump will be 12.5kw Daikin or Panasonic with Airtouch 5)

Heatpump usage patters: Summer 5pm to 12am to cool lounge and bedrooms. Spring / Autumn - None. Winter 5pm - 10am heating.

Request: Could I have your advise as to whether we should retain the DVS system, Buy a new ERV with the ducted heatpump or forget about the ventilation.

Options:
(1) Remove DVS and utilise new ducted heatpump only - add ERV in future if necessary
- Concern that when heat pump not running there is no circulation
- Concern that we will begin to have condensation in winter
(2) Retain 3/4 or the DVS outlets (garage, hallway, living, spare bedroom) for the purpose of ventilation (this air would likely be fed around the house by the heat pump system
- Concern that when heat pump not running many rooms won't receive the ventilation (only really works if heat pump is on)
- Lots of ducting in ceiling and extra outlets in house.
(3) Add ERV system to the Heatpump system
- Is ERV taking outside air going to add humidity to the home in winter? Unlike our attic DVS.
- Can the system (managed by Airtouch) be smart and just use ERV for ventilation most of the time except the hours mentioned above when active cooling and heating are required?

For this discussion, money is not an issue. I believe an ERV unit will be about 3000 dollars extra.

SECOND QUESTION:
One vendor has recommended round diffusers as outlets. Another has recommended linear grills. The grills look a lot nicer. Any recommendations or features I should ensure the outlets have? For example I'm thinking of asking if they can be adjusted to move air down or up.

lxsw20

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#3353394 13-Mar-2025 11:36

We are in process of building, our system will be a ducted heat pump connected to a fresh air heat exchanger. (Daikin equivalent of Mitsubishi Lossney)

It would be worth talking to your heat pump installer about a system like this. This way you're pulling fresh warm air in, rather than an EVR and heatpump competing with each other.

timmmay

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#3353467 13-Mar-2025 13:17

Have a read of this ducted heatpump FAQ.

What I did was put the ventilation system output close to the ducted system return grill, and put the ventilation system on a timer. Once a day I turn on ventilation and the ducted heat pump to fan mode to push fresh air around the house. I turned the ventilation system on sometimes when the ducted system is heating or cooling as well. It's a reasonably good and fairly simple solution. Getting an ERV is a better solution, but is it better enough for the cost? Not sure about that one. I have no plans to get an ERV.

Linear grills, the MDO ones that can push air in different directions, are significantly better than the round outlets. The round ones often just push air across the ceiling, but it depends on how the air is exiting the room back towards the return grill. Wall / door vents are often better than undercut doors, as you need more undercut than you'd expect - a couple of cm which is weird looking.

tweake

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#3353715 13-Mar-2025 17:21

i'll try to come back to this later, its been a long day.

basics, it depends on grill locations. most likely the ventilation grills will be in the wrong location for heating/cooling. so the options are either leave the DVS as is or remove the DVS grills and fix up the ceiling. having two grills can make it look a bit poor but its the cheapest and easiest solution, just install the heat pump system and its done.

DVS vers ERV, unless the house is reasonably air tight i doubt the erv will bring much benefit, especially for the cost. i think the biggest problem will be how well the house is insulated. concrete block (ie breeze block) are typically not insulated (and yes nz building code does allow that) but if its is its important to know how its done. also ERV keeps moisture IN a home (as well as keeping moisture out), so you need a way to manage moisture levels or at least measure humidity levels. one of the ways concrete block houses are insulated is with pir/iso panels, which do not allow moisture to go through it (ie stops the house from drying) which means you have to be extra careful with moisture management if you have that system.

generationy

5 posts

Wannabe Geek

#3353898 14-Mar-2025 10:56

lxsw20:

We are in process of building, our system will be a ducted heat pump connected to a fresh air heat exchanger. (Daikin equivalent of Mitsubishi Lossney)

It would be worth talking to your heat pump installer about a system like this. This way you're pulling fresh warm air in, rather than an EVR and heatpump competing with each other.

Yes actually this was the type of setup im contemplating. Using Lossnay for most of the year ventilation (circulation) an heat pump when needed.

generationy

5 posts

Wannabe Geek

#3353899 14-Mar-2025 11:00

timmmay:

Have a read of this ducted heatpump FAQ.

What I did was put the ventilation system output close to the ducted system return grill, and put the ventilation system on a timer. Once a day I turn on ventilation and the ducted heat pump to fan mode to push fresh air around the house. I turned the ventilation system on sometimes when the ducted system is heating or cooling as well. It's a reasonably good and fairly simple solution. Getting an ERV is a better solution, but is it better enough for the cost? Not sure about that one. I have no plans to get an ERV.

Linear grills, the MDO ones that can push air in different directions, are significantly better than the round outlets. The round ones often just push air across the ceiling, but it depends on how the air is exiting the room back towards the return grill. Wall / door vents are often better than undercut doors, as you need more undercut than you'd expect - a couple of cm which is weird looking.

Thank you of the link - a lot of pages to read through.
1) ok you've backup my idea about ducted system and DVS together are a possibility. I'll just see how much it is to get the ERV (Lossnay or similar) installed. I think the installer said its about 3k.
2) Ok that's the second person that has said the round outlets are fairly poor.

generationy

5 posts

Wannabe Geek

#3353903 14-Mar-2025 11:08

tweake:

i'll try to come back to this later, its been a long day.

basics, it depends on grill locations. most likely the ventilation grills will be in the wrong location for heating/cooling. so the options are either leave the DVS as is or remove the DVS grills and fix up the ceiling. having two grills can make it look a bit poor but its the cheapest and easiest solution, just install the heat pump system and its done.

DVS vers ERV, unless the house is reasonably air tight i doubt the erv will bring much benefit, especially for the cost. i think the biggest problem will be how well the house is insulated. concrete block (ie breeze block) are typically not insulated (and yes nz building code does allow that) but if its is its important to know how its done. also ERV keeps moisture IN a home (as well as keeping moisture out), so you need a way to manage moisture levels or at least measure humidity levels. one of the ways concrete block houses are insulated is with pir/iso panels, which do not allow moisture to go through it (ie stops the house from drying) which means you have to be extra careful with moisture management if you have that system.

Thanks Tweake.
I'm leaning towards getting of most of our DVS (just retaining for the garage) and adding a ERV (Lossnay type). We are out of the house quite a lot and it would be good to have ventilation on during that time. I might need to seal up your leaky front door though.

We are concrete blog but it's all insulated and with Jib so it's quite warm.

Hopefully the Airtouch system will work well with ERV as I'd like it to run in ERV mode a lot.

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tweake

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#3354018 14-Mar-2025 16:08

generationy:

Thanks Tweake.
I'm leaning towards getting of most of our DVS (just retaining for the garage) and adding a ERV (Lossnay type). We are out of the house quite a lot and it would be good to have ventilation on during that time. I might need to seal up your leaky front door though.

We are concrete blog but it's all insulated and with Jib so it's quite warm.

Hopefully the Airtouch system will work well with ERV as I'd like it to run in ERV mode a lot.

an ERV should run all the time. its all about constant ventilation rather than variable ventilation the DVS gives.

the tricky thing is integrating it into the ducted heat pump as you need the heat pump fan to be running to circulate the air. have a look at some of the issues found in some recent threads.

the more i've seen of the lossnay the more i'm starting to dislike them (it needs the controller). if Panasonic heat pump is an option then look at Panasonic ERV. ideally try to use the same brand erv and heat pump as eg the Panasonic heatpump controller also does the erv. also i think the Panasonic you can run without needing a controller (i'm not sure on the models we get here as they are fairly new).

afaik airtouch doesn't do erv's, but with a good erv you should never need a controller. you set it and leave it to run all the time.

raytaylor

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#3355270 19-Mar-2025 16:57

I cant remember the specifics of the DVS system but we have heat pumps in our house in addition to an HRV system.
The reason is that the heat pumps, even if ducted, recirculate air and when not cooling they wont be dehumidifying.
So the HRV/DVS would be bringing in dry air to prevent mould.

ALSO

I like that in winter, i can set the temperature on the HRV to max/27 and on a sunny day and heat up the house with the power consumption of a desk fan.
While no one is at home during the day, the mass in the living space absorbs that heat and releases it into the evening.
Then we dont need the heat pump system do do any work until later into the evening.

Ray Taylor

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AklBen

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#3438940 1-Dec-2025 12:11

Had a good read of this thread and we're in a similar situation...wondering if we keep or ditch when installing a ducted system house-wide?

1989 3 beddy, single glazed, fairly well insulated home in Auckland. Has an (actually branded) HRV system with vents in all bedrooms.

I understand by reading on here and a few reddit threads that people have opted to keep them to help with condensation and some transferring of the ceiling temps on advantageous days to keep heating or cooling costs down.

The reason why I wonder about removing the HRV unit is reducing the number of vents in the ceiling as then each room will have two vents and it's not the most attractive. I also wonder if it's redundant and just another thing to 'manage' and figure out if the new heat pump system will just do the job well enough?

Appreciate any advice or thoughts.

generationy

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Wannabe Geek

#3439022 1-Dec-2025 14:06

Ok so this is where I got to...

The HRV offers zero benefit in the summer so let's take that out.

In Autumn / Spring it might make things a little better in the day so there is a positive. It also allows you to keep all your windows closed at this period (we have a big allergy sufferer in the house) and still get fresh air in. We didnt use our ducted aircon hardly at all during these periods.

In Winter, I tried it out in our home with just heating on and HRV off and no condensation in our home. So I could go without it in my home.

One item, the aircon guy didnt want to reuse the positions of our HRV anyway so even if you get aircon your going to need to cut new holes and then jib up the HRV holes.

So my recommendation would be to keep the HRV, try a season of winter and see if you need the HRV or not. If you dont you can take it out next time you paint the ceiling / redecorate a room.

IN GENERAL

After living with our ducted aircon for 6 months (zoned) I would say that if you have a house that gets condensation then HRV should be kept or you get a similar system that connects to your ducted unit. If you like to keep your windows shut (like us) then HRV has value. If neither of those are key then take it out.

I really appreciate the ventillation the HRV provides, particularly while we are away. So in the future I'll upgrade to a lossnay style unit and get rid of the HRV just to tidy things up.

AklBen

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#3439024 1-Dec-2025 14:14

Thanks for your response and that was what I was wondering about looking into a lossnay unit while we're getting the ducted system done all in one whack and then when we get the roof done (another project) get it and the heat transfer system gone.

One thing that I find slightly confusing is folks referring to "fresh air" from the HRV. Fresh air from a dusty ceiling/roof cavity?

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timmmay

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#3439027 1-Dec-2025 14:25

My ventilation system originally had a sock filter and pulled in ceiling cavity air, but the filter turned from white to gray pretty quickly. I modified it to pull air from the eaves and through a decent filter system - I got a three filter from Ali Express that is pre-filter, charcoal filter, and HEPA filter. It works well. We never need to open windows because the ventilation system pushes fresh filtered air into the house and the ducted system pushes it around.

tweake

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#3439068 1-Dec-2025 16:59

generationy:

The HRV offers zero benefit in the summer so let's take that out.

sorry but thats absolutely BS. not true at all. not even remotely close.

every house REQUIRES ventilation all year around. the only time it doesn't is when there is no people living in it. its been proposed for commercial buildings but residential there is next to no energy saving by turning it off. while you technically don't need ventilation when your away, because most positive pressure systems are not continuous, the house tends to act as storage and needs airing out. the only houses that don't are those that are so drafty they are flowing more air through than a ventilation system provides.

condensation is not WHY you need ventilation. the old crying windows thing is more marketing than reality. its not there to get rid of condensation and condensation is not a marker for bad ventilation. co2 levels is a much better marker.

if you have people in a home, you NEED ventilation. either open windows and doors (as we have traditionally done) or automate it with a ventilation system. however ventilation systems do a better job as opening windows only works if there is wind and is highly variable due to wind strength.

so leave the HRV/ventilation system in, or integrate it into the ducted hvac system.

tweake

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#3439071 1-Dec-2025 17:07

AklBen:

Thanks for your response and that was what I was wondering about looking into a lossnay unit while we're getting the ducted system done all in one whack and then when we get the roof done (another project) get it and the heat transfer system gone.

One thing that I find slightly confusing is folks referring to "fresh air" from the HRV. Fresh air from a dusty ceiling/roof cavity?

lossnay or other balanced systems depends on a few things. some of this is somewhat debatable, primarily because most nz homes are very air leaky. positive pressure systems are (or at least should be) cheaper for similar performance in air leaky homes. also erv's have their own quirks.

"fresh air" etc is all marketing, take everything with a bucket of salt. there is a fair bit of airflow through ceiling spaces and the ventilation system can remove all that air fairly quickly on smaller roof spaces. but an external air inlet (aka summer kit) works well. not hard to make your own automatic summer kit so it uses ceiling space air when its cold and outdoor when its hot.

raytaylor

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#3440517 5-Dec-2025 18:04

generationy:

In Winter, I tried it out in our home with just heating on and HRV off and no condensation in our home. So I could go without it in my home.

Just a point on that part - your fabrics, furniture and bedding etc will absorb moisture first. Over time, the fabrics will slow the rate of absorption, leaving moisture in the air for longer which then has the opportunity to condensate on the windows or cold surfaces.

So it wont necessarily just take one winter before its noticeable. Its really a build up over a long time.

Ray Taylor

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