Conflicting advice from Central Ducted Heat pump installation companies

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Slippery

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#295841 27-Apr-2022 16:59

I'm looking at getting a Central Ducted Heat pump installed at my 2018 built 157m2 3 bdrm house and have received conflicting information from the two companies that I contacted. Help around the below topics is really appreciated

1. Zoning
The First company suggested that zoning is not required for our place as it isn't that big. He also suggested that a ducted heat pump is more efficient when run continuously and we should run it throughout the winters like for 6 months non-stop. Heating up a cold house takes more energy than maintaining the house to the set temperature.

The second company suggested that we get 4 zones, 1 for the living room and 1 for each bedroom. The rationale being able to better control the temperature and save on the cost by not heating unoccupied rooms while sleeping.

Is zoning worth it and if so do I need a separate zone in each room? My living room gets morning sun and one of the bedrooms gets the evening sun. Not a very sunny house.

Does zoning save power and running costs or the opposite?

2. Fresh Air intake duct

One company suggested we add a small duct which will continuously bring in fresh air from outside and thus create positive air pressure within the house. He told us this will improve the house's air quality (co2 level), reduce condensation, and won't add much to the running cost.

The other installer told us that it's not required and we should open our windows for 15 mins a day as positive pressure isn't good for the house as air looks for new routes to escape.

What's your experience with fresh air intake ducts?

How much does it add to the running cost and can it bring in moisture when it's raining/humid outside?

3. Air circulation in the bedrooms

One person said that the door should be open for good air circulation and temperature control (not ideal as we have a kid) while other said that 1 cm of clearance below the door is enough, which I have.

4. Automation

One company suggested we install Airtouch with a Diakin Heat pump, which will let us control the unit remotely and can also control other smart home devices in the house.

If we are to run the unit nonstop then is there even a point? On the other hand, if remote control is useful then which heap pump is able to integrate well with home automation software? I've played with Openhab in the past but Google did not return much info on Airtouch integration with Openhab.

5. What else?
Given the differences in the opinion between the two companies I want to know what else should I be asking/clarifying with them. A tad bit nervous here wasn't expecting this.

timmmay

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#2907636 27-Apr-2022 17:34

Have you read my ducted heatpump experience thread? You may find it interesting. My opinion, as a ducted heat pump owner.

1. Definitely, absolutely zoned, no question. This goes double if any of the rooms gets more sun than the others. Ideally you want automatic temperature control with something like Airtouch4, but you can get away with basic zoning if you can't afford that. I think it will increase comfort significantly. Running cost, might help a bit. You don't need to leave it running 24/7, but through use of timers and such turn it on a couple of hours before you get home at least. I'm using Home Assistant for automating my Airtouch.

2. I have one, mostly because it was there before I got the ducted heat pump. I like it. The positive pressure output is beside the ducted heating input. This gives the ability to turn the ducted system to fan mode and push fresh air to each room. I only have the positive pressure system on when I want it on, it's on a WiFi timer which I control with Home Assistant. We crack the windows (double glazed so just open 1cm), turn on positive pressure ventilation, turn on the ducted system to fan only, if you stand outside the window you can feel air going out to match the fresh air coming in. With it on a timer it won't increase running cost much.

3. One cm clearance might be enough. Have a look at the thread above at the wall vents I use also this and this. I have doors closed and vents are always open, they let air through but not much noise or light.

4. Yeah I like it. It's not perfect, but it's way better than no room temperature control. One thing to do is look in the Airtouch installer manual and get "Bypass Mode" installed, otherwise your spill zone can overheat sometimes. Make sure you don't get an oversized heat pump, that increases spill - sometimes ramping down to a low output is more important than maximum power when a ducted system is on most of the time.

5. Read that other thread, read this, then ask questions :) I spent AGES learning about this stuff, and had my first system removed because it wasn't great. Diffuser selection is really important to air distribution and low noise. Having a good installer is important, high volume of installed systems doesn't mean good - hard to say how to find a good installer though - maybe look at who Daikin recommends.

Dingbatt

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#2907642 27-Apr-2022 17:54

If you can afford it, go with zoning. We don’t have it in our ducted system and it leads to uneven temperatures. At a minimum divide the system into bedrooms and living areas.

We use under door gaps for the return air. Once again it does the job, but return grills would be better.

It is my intention to include wireless control. If any of the companies I contacted actually bother to respond that is.

“We’ve arranged a society based on science and technology, in which nobody understands anything about science technology. Carl Sagan 1996

mclean

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#2907673 27-Apr-2022 19:34

It takes MORE energy to keep the whole house at the set temperature. If an installer tells you otherwise then he doesn't understands heat loss and I'd be looking for someone else.

Zoning reduces the running cost, but it costs more to install. If you can afford it then, as a minimum, zone the living and sleeping areas separately.

Bringing the fresh air in via the AC system doesn't change the running cost - it's the same fresh air, whether it comes in through the AC system or the windows - for the same ventilation rate the running cost is the same.

10mm door undercut isn't enough. 25mm might work. Door grilles or wall transfer grilles definitely work.

You get very little benefit from a zoned system unless the return air is also zoned. For example, if you're heating say the bedrooms, and the return air has to pass out of the bedrooms into an unheated space (like the living areas or a shared hallway) on its way back to the unit, then the unit has to work MUCH harder. I've seen houses where this mistake can result in the system not working at all. Each zone needs its own return air path. The best way is to have a separate fan-coil and return air system for each zone. A cheaper option is to have a shared fan-coil, and control the return so that it draws air only from the spaces that are operating.

This is the thing that installers most often get wrong, and results in high running costs.

timmmay

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#2907678 27-Apr-2022 20:01

I'm going to respectfully disagree with @mclean on a couple of points, though I generally agree with most of what he says. Fresh air, undercut, running cost, fully agree.

Regarding zoning, I wouldn't do two zones only. I wouldn't bother with a ducted system unless it's fully zoned, and ideally with per-room temperature control. Our experience with one sunny room and one shady room showed that without good zoning the temps will be very different between rooms particularly Autumn / Spring when the sun is lower in the sky which is quite frustrating. Today it was sunny, before I turned the system on the lounge was 20 degrees and one bedroom was 25 degrees. What I did there is first turned the fan on to push a bit of that warm air into the lounge, which worked a bit, but in practice we have to air condition the hot room down to where we want it, then change to heat mode and heat the rest of the house.

Regarding zoned returned air, I disagree that it's essential. Zoned returns would be good in some cases, but if most of your rooms come off a central hallway then I've found a central return works very well. However, if you have distinct areas with doors between them that are often closed then multiple returns may be useful or necessary. For example, we have a ducted system into the lounge and three bedrooms which all come off the hallway, it works great. Our kitchen / dining uses a highwall because that area gets a lot of sun, so we often need to cool that area while heating the rest of the house. If we wanted to include the kitchen in the ducted unit we would need another return because it's quite a way for air to be pulled, and I'm not sure a simple wall grill would be enough.

A possible downside of per-room returns is the conditioned air is pushed in from the ceiling in most installs, with a zoned return it's pulled out from the ceiling. The risk particularly with the simple round diffusers is the air runs across the ceiling rather than mixing with the room air, giving you heat stratification - hot ceiling cold floor in heat mode. That's what my first system ended up with, because the supply diffusers were rubbish. If you have a return grill near the floor the air is pushed in at the ceiling, pulled down towards the ground, distributing the air better across the room. If you have the right diffuser, downjet or the square ones I recommend in my other thread, per-room returns could be made to work.

One thing an installer told me was try to get the return at floor level if the diffusers are at ceiling level. This usually means you want an intake near the ground, then a 300 - 400mm pipe going up into the ceiling to return air to the indoor unit. If you have a cupboard in a central hallway that can apparently work ok, air goes in the bottom, through the cupboard, and is taken out the top.

Handle9

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#2907687 27-Apr-2022 20:33

Ducted units can be great but if you have one unit for the whole house you need to accept that it will be always be a compromise. You will never achieve perfect temperature for the whole house. You have one fan and one coil, regardless of how you zone using dampers.

If you have relatively constant loads it can work very well but it’s not really the way that ducted units are designed to work from the factory.

mclean

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#2907817 28-Apr-2022 09:55

timmmay: Regarding zoned returned air, I disagree that it's essential. Zoned returns would be good in some cases, but if most of your rooms come off a central hallway then I've found a central return works very well...

I guess it depends on where you are. In my house (Kapiti) the unheated spaces can drop to 10 degC in the winter early morning hours. That's a 10-12 degC penalty in sensible load if the return air was drawn from that area. Obviously less in the off-peak seasons.

A central hallway works a lot better for return air if there's a door between it and the living spaces which can be closed at night.

timmmay

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#2907821 28-Apr-2022 10:12

mclean:

I guess it depends on where you are. In my house (Kapiti) the unheated spaces can drop to 10 degC in the winter early morning hours. That's a 10-12 degC penalty in sensible load if the return air was drawn from that area. Obviously less in the off-peak seasons.

A central hallway works a lot better for return air if there's a door between it and the living spaces which can be closed at night.

I'm in Wellington. Our very old house is well insulated and double glazed. On a really cold night unheated spaces might drop to 16 degrees, but usually only 18 degrees. Because of the way Airtouch works there's usually a bit of spill into the spill zone, which for us is the lounge, so that stays warm ish.

The doorway between our hall and lounge can't be closed, it's open plan, it works fine. I guess it just depends on the specifics of the house.

If you have the return in a central hallway, heating of the bedrooms overnight keeps the hallway fairly warm. I'm not really sure what your scenario is, why the return would be somewhere that gets so cold with the return there. Do you have a ducted heating system or experience with one you're basing your opinions on?

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mclean

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#2907831 28-Apr-2022 10:30

timmmay: I'm in Wellington. Our very old house is well insulated and double glazed. On a really cold night unheated spaces might drop to 16 degrees, but usually only 18 degrees. Because of the way Airtouch works there's usually a bit of spill into the spill zone, which for us is the lounge, so that stays warm ish.

The doorway between our hall and lounge can't be closed, it's open plan, it works fine. I guess it just depends on the specifics of the house.

If you have the return in a central hallway, heating of the bedrooms overnight keeps the hallway fairly warm. I'm not really sure what your scenario is, why the return would be somewhere that gets so cold with the return there. Do you have a ducted heating system or experience with one you're basing your opinions on?

Yes indeed, it depends on the house. Sounds like yours is all good.

No, I don't have one in my house. I'm an HVAC engineer (of the professional type), so I've designed and trouble-shot more than a few.

timmmay

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#2907836 28-Apr-2022 10:43

mclean:

Yes indeed, it depends on the house. Sounds like yours is all good.

No, I don't have one in my house. I'm an HVAC engineer (of the professional type), so I've designed and trouble-shot more than a few.

Ah nice, a professional. Do you do all the design properly like I've seen the engineers do in the USA, or do you do like NZ places usually do and take a guess and chuck it in?!

Either way, you have more experience than me, my experience is one house / two systems. My experience doesn't seem to completely agree with yours though, but that might just be the properties you've worked on are different from mine.

mclean

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#2907870 28-Apr-2022 12:08

timmmay: Ah nice, a professional. Do you do all the design properly like I've seen the engineers do in the USA, or do you do like NZ places usually do and take a guess and chuck it in?!

You know my answer to that question! But for small residential work, most homeowners don't want to pay for professional services design. That's usually left to the architect or contractor/installer, and it's the same worldwide. We might get asked to recommend a contractor that knows what he's doing, but mostly our involvment starts when things have gone wrong and lawyers get involved.

mdf

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#2907881 28-Apr-2022 12:34

mclean:

You know my answer to that question! But for small residential work, most homeowners don't want to pay for professional services design. That's usually left to the architect or contractor/installer, and it's the same worldwide. We might get asked to recommend a contractor that knows what he's doing, but mostly our involvment starts when things have gone wrong and lawyers get involved.

Do you actually offer independent design services to retail customers? Because this would certainly be a service I would be interested in at some stage - we've actually got gas ducted central heating and I'm not super happy with it. With gas ultimately on it's way out, I'd be interested in a switch to electricity at some stage and - one bitten, twice shy - very happy to pay someone independent who knows what they are doing to recommend a solution rather than wing it with a salesperson.

Danite

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#2907905 28-Apr-2022 14:01

I have two systems installed, one for the lounge/lounge/kitchen/office area ~120sqm and another for 4xbedrooms bathroom and hallway ~90sqm, I have no zoning. I went with two units as the areas are on separate sides of the house East/West so can be quite different temps and made it easy to not run an area and leave doors closed. I also had good access to cheap pricing and did a bunch myself.

Lounge one works great and wouldn't change anything.

Bedrooms is a smaller unit and does an ok job, if I did it again I would consider going with a unit that has higher airflow rate but works ok as is. I would also have put individual returns in the cupboards and cut the doors ~20mm as I have found that having a central return in the hallway and outlets in all the bedrooms it can be very dependent on which bedroom doors are shut as to what the system does/how warm/cool the rooms get. I like the idea of having them in the cupboard as they would effectively be invisible, no vents in main bedroom door or in the wall, but I understand some people might not like the idea.

I actually think ducted heat pumps are great for evening temperatures out in a house where you have a hot room on one side and cool on the other as the warm air gets sucked to the return and then redistributed to the rest of the house though @timmmay has found this not so true at his place, might just be a really warm room!

Disclaimer: I am an electrician and did a bunch of the work myself, got a fridgie in to run his eye over it and to vac and gas it. I think it has come out ok and haven't been motived enough to change anything yet but if I can be bothered might one day add the cupboard returns as I do think that would make a big difference in not having to heat/cool the hallway and give greater temp control over each room. I'm guessing this would require adjustable dampers on the supply to each room and on/off dampers on the return from each room but haven't thought a whole lot about it @mclean might be able to help me out with advice there!