Advice on whether to go with ducted or multi-split heat pump system

Forums › Home Workshop DIY › Advice on whether to go with ducted or multi-split heat pump system - paralysis by analysis

mda180

3 posts

Wannabe Geek

#288697 17-Jul-2021 13:11

Heya everyone,

A bit of a long post here, but thought it may be good to give some context! I've got myself fairly stumped here and would be awesome to get some Geekzone advice.

I'm a first time home owner at a 1950s house. I'm a 29yr old single guy who is quite scared with the amount of debt over my head, and really need to be careful about what I decide to sink money into with the house. Mulling on it all is keeping me awake at night.

I know the way things are with heat and moisture isn't sustainable or healthy though, so I really want to get on to that asap. The first winter in the house is proving a learning experience. We are struggling with it being pretty cold, and quite a bit of condensation on the windows if they aren't left open overnight (which is not appealing when its minus 4!!!)

The house used to be a flat roof, with an arched one put over top of the old bitumen roof.One company thought this would be an issue for going ducted, but 3 others think they can work through it fine, as there is a large roof space above the old roof.

I am living with 2 housemates who are probably what you would call 'room bodies'/ gamer dudes. We all have oil fin heaters in our rooms, and an old heat pump in the lounge that doesn't get much use at the moment, as we aren't out there a lot.

There is an old DVS system at the property with a single vent in the hall, but it is not working at the moment. I had DVS in to look at it, but instead of going up to check what was wrong with it, they tried to upsell a very expensive positive pressure system which i'm not convinced will address my main issues. In any case, with it only having the vent in the hall and being so old, I don't know if its worth getting it serviced.

The main thing I am grappling with is whether to do ducted or with a multi-split system.

The ducted would have vents in all 3 bedrooms, 1 in lounge, 1 in kitchen. With return in the hall. A multi, I would be looking to either only get a 3 head which services the bedrooms, and leave the old heat pump there to be replaced at some point, or replace the lot at once, and use the existing concrete pad where the old pump is. This would avoid having a second external box outside, and the heat pump is pretty old, so am thinking it could be better doing the lot.. If I go ducted, I think it would just be left there till I can afford to do something with it.

With the way we live at the moment, the ability to have further control and only heat parts of the house does appeal. But in saying that, having more central heating I wondered whether it could be healthier over all, and maybe be a bit cleaner and better in terms of resale (as i'm aware the pipe work etc is a bit messy with multi).

I have worries about the power bill with the ducted approach though. And if there are times when really only one room is being used, it seems quite wasteful to have to heat the whole house.

I do like the idea that ducted would keep some more constant air flow going though, which makes me wonder if a separate ventilation system is worth investing in on top of a multi, if I go that route. It all adds up to a lot, and the ducted vs multi seems fairly similar price wise atm, but ventilation on top is a few extra grand.

I've had quotes from a lot of companies now, and I feel a bit bad to have mucked any of them around, but really just trying to make sure I do my due diligence on options. Now i'm completely overwhelmed with info.

At this stage, I think i would like to go with mitsubishi unit. But which option, i'm very lost on.

I'm not usually such an indecisive person, but a bit going on with work and losing my uncle last week, hasn't got me in the best decision making frame of mind.

Any advice would be awesome - though I'm slightly worried posting this about just getting myself more stumped!

Need to just make a call I think.

Thanks everyone.

RunningMan

8956 posts

Uber Geek

#2745761 17-Jul-2021 13:59

Sorry to hear about your uncle.

A benefit of ducted is the ability to draw fresh air into the system, however most 1950's houses would have so many air leaks (i.e. natural ventilation) it's not really of as much benefit to you. Multiple split systems make it much easier to isolate heating to specific areas only - it can be very difficult to properly balance a ducted system to work with only some areas at a time. The air flow (therefore temp) will also change significantly as doors are closed or opened with a ducted system. Ducted would work best in open plan or areas where the airflow won't change - i.e. the doors are always open, or always left closed. Given the way the house is used, and likely has natural ventilation, I'd go for several split systems.

You can have multi split with several indoor off a single outdoor unit, or just several split systems. Compare prices and aesthetics of each. As for forced ventilation, very good idea on a modern airtight building, but questionable if required at all on an old leaky (air) building.

timmmay

20581 posts

Uber Geek

Trusted

Lifetime subscriber

#2745774 17-Jul-2021 14:48

First: only take advice on ducted units from someone who has one. I have a Daikin ducted with Airtouch 4 zoning, I had a Panasonic ducted taken out as it was super loud and had other problems. Previously had Fujitsu and Daikin Highwalls.

Second: multi-split is probably better for you and likely cheaper

Third: read this thread. Don't buy Panasonic, I would only consider Daikin or Mitsubishi.

Multi-split advantages:

More efficient as the whole system other than copper pipes are within the insulated envelope. With ducted you have big ducts in the ceiling that aren't all that well insulated that loose a fairly bit of heat
Gives individual room temperature control, though they all have to be on one mode (heat / cool). With ducted you can get this but it costs $2-3K more and even then the control isn't near as good as units in each room
Much simplier to install - ducted takes 2 days, huge holes cut everywhere, you might need two returns. Ducted worked better with floor level returns, and you need to be careful with your diffuser choice so the ceiling doesn't get hot with the floor staying cool
No need for vents to allow air to exit the room. With ducted you need 1-2cm cut off the bottom of the doors, or a vent in the wall / door to allow air to return. Without this the rooms become pressured and the air return doesn't work. Bad things can happen.

Ducted advantages:

Quieter
Nothing on the walls
They don't tend to have fresh air inputs, but if you have a standard positive pressure ventilation system with an outlet near the return vent you effectively get fresh air input
Tends to be whole house, though we just did half hour house as one area gets so much sun it needs its own dedicated unit

With ducted you really need zones with manual or automated room controls. If you don't have this then north facing rooms get super hot while south facing rooms stay cool. You can tune the fixed dampers on the ducts but these need to be different on sunny days / cold days.

Either way insulation is important.

Happy to answer questions. Probably won't reply until tomorrow.

mda180

3 posts

Wannabe Geek

#2745780 17-Jul-2021 15:07

Thank you both so much for the thorough replies here.

Really appreciate it. I was leaning to think the multi-split is a better bet for my situation, so this is good reassurance.

At this stage I'm wondering if leaving the heat pump system in the lounge as an independent unit is a better bet. Or replacing the lot at once, with that being one of the 5 units making up the multi-split. Having it separated out appeals in terms of no one single point of failure, i.e. if the lounge system fails, still have the bedroom multi going.

In doing that though, the kitchen/dining area wouldn't have any unit in it though - its across the other side of the house so might need another external unit and i'm not sure its worth it. I can open the door between the living area and lounge to let heat through that way.

The two options I am looking at most closely:

1:Mitsubishi MXZ-5F100 Multi condensing unit. $ 12,660.00
Capable of 10.0kW of cooling and 10.0kW of heating.
3 x MSZ-AP20 high walls one for each bedroom.
1 x MSZ-AP25 high wall for the kitchen area.
1 x MSZ-AP35 high wall for the lounge.

I think this sounds good, but have some concern re 10kW being enough to support 5 split heads?

or

2: (this doesn't include head in the kitchen - but might ask them to add to quote):
Supply and Installation of 1 x Daikin 5MXM100RVMA multi split outdoor unit rated at 11.0kW heating / 10.0kW
cooling, connected to 1 x CTXM50 & 3 x CTXM20 high walls
Indoor unit location: at high level in the Lounge & 3 Bedrooms (services to be run out via wardrobes)
Outdoor unit location: at ground level in place of the existing unit
Please note, this quote is subject to a final site inspection to confirm pipe runs, unit locations, etc
Total NZD 10,450.00

3: - I am quite confused about this quote - how much it would end up being. 2 options outlined but a bit confusing.

Whole House
Supply, Install & Commission 1 x Daikin FDYAN85AV1/RZA71CV1 Ducted - 10.0kW Heat / 8.5kW Cool
Air Handler Location: Centrally located in the ceiling
Outdoor Condenser Location: At low level outside where current outdoor unit is
Conditioned air to be supplied to the following areas;
Living - 1 x Eco Automatic Round Ceiling Diffuser
Kitchen - 1 x Eco Automatic Round Ceiling Diffuser
Bedroom 1 - 1 x Eco Automatic Round Ceiling Diffuser
Bedroom 2 - 1 x Eco Automatic Round Ceiling Diffuser
Bedroom 3 - 1 x Eco Automatic Round Ceiling Diffuser
Return air to be taken from the following areas;
Hallway - 1 x 600x600mm Egg Crate Grill w/ Filter
Please note that this option is possible as you do have the roof space but we have not included any of the builders work
required to make this possible that you will have to arrange yourself.
Sub-Total ex GST $10869.57
Section Sub-Total ex GST $10869.57
GST $1630.43
Section Total inc GST $12500.00

Option upgrade to Ducted Heat Pump
Intergrated Balanced Ventilation System
Supply and Install 1 x Daikin balanced ventilation system including
1 x VAM- VAM350GJVE Heat Exchange & Fan unit controlled via the duct heat pump
1 x 300mm sq intake grill in the Living Area
3 x 200mm round supply duct connected into the return side of the ducted heat pump
1 x 200mm sq outside air intake grill
1 x 200mm sq exhaust air grill
and all necessary ductwork and components required.
Sub-Total ex GST $4521.74
Section Sub-Total ex GST $4521.74
GST $678.26
Section Total inc GST $5200.00

Outdoor Condenser
Supply & Install 1 x Daikin 5MXM100RVMA - Rated at 11.0kW Heat / 10.0kW Cool
Location: At low level outside where the current existing units sits
Sub-Total ex GST $5043.48
Living Area
Supply & Install 1 x CTXM25RVMA - 2.5kW Class High Wall Model
Location: At high level in the place of the existing indoor unit
Sub-Total ex GST $1217.39
Kitchen
Supply & Install 1 x CTXM20RVMA - 2.0kW Class High Wall Model
Location: At high level on the wall by the window
Sub-Total ex GST $1217.39
Bedroom 1
Supply & Install 1 x CTXM20RVMA - 2.0kW Class High Wall Model
Location: At high level above the wardrobe
Sub-Total ex GST $1217.39
Bedroom 2
Supply & Install 1 x CTXM20RVMA - 2.0kW Class High Wall Model
Location: At high level above the wardrobe
Sub-Total ex GST $1217.39
Bedroom 3
Supply & Install 1 x CTXM20RVMA - 2.0kW Class High Wall Model
Location: At high level on the on the wall that backs onto bedroom 1 between to the two doors
Sub-Total ex GST $1217.39
Section Sub-Total ex GST $11130.43
GST $1669.57
Section Total inc GST $12800.00
Condensate pump price per heat pump, note you will only be charged for this if we require
Sub-Total ex GST $278.26
Section Sub-Total ex GST $278.26
GST $41.74
Section Total inc GST $320.00
Supply and Install 1 x Mitsubishi Electric balanced ventilation system including
1 x Lossnay LGH-35RVX Heat Exchange & Fan unit incl Digital Control
1 x 300mm square intake grill in the kitchen or living
5 x 150mm round supply grills in the bedrooms and living
1 x 200mm sq outside air intake grill
1 x 200mm sq exhaust air grill
and all necessary ductwork and components required.
Sub-Total ex GST $5043.48

fe31nz

1232 posts

Uber Geek

#2746063 18-Jul-2021 00:28

mda180:

In doing that though, the kitchen/dining area wouldn't have any unit in it though - its across the other side of the house so might need another external unit and i'm not sure its worth it. I can open the door between the living area and lounge to let heat through that way.

This will simply not work. Unless there is active airflow through the door (put a fan there), then you will not be able to heat the kitchen/dining room from the living room heat pump. If the living room heat pump faces the door directly and can blow through it, it might work somewhat, but even then the living room unit will not have enough heat output to do the kitchen/dining area as well. Kitchens in old homes need good heating if you want any chance of a comfortable breakfast on frosty days, so I would not recommend economising on kitchen heating.

We have a three bedroom 1955 house where we just put individual heat pumps in all rooms that needed one - kitchen, dining room (computer room these days), sitting room and two of the bedrooms. The middle bedroom is only used for guests a couple of times a year, so it just has an old fan heater. When we did this, multi-splits were not really available so we did not consider them. One of the big advantages of one unit per room is that the smaller rooms get smaller units and the smaller a heat pump is the higher its efficiency, so the bedroom units do 4.2 ratio, even though they use the older, less efficient, refrigerant. We had the advantage of not needing to put in any concrete or the like for the outdoor units as we already had a concrete path right around the outside of the house and they could just be bolted to that. And there was no problem running electricity to them either - the house being on piles and having a normal roof shape the wires could easily be run to each unit. The only complication was with the sitting room indoor unit which had to be sited on an internal wall, and the run for its condensate pipe to the outside wall needed an extra condensate pump in the ceiling.

If you are suffering from high heating bills at the moment, as a general rule heat pumps will not reduce it much - instead, what usually happens is that the heating bill remains the same and the house becomes comfortably warm instead of very chilly.

mda180

3 posts

Wannabe Geek

#2746165 18-Jul-2021 10:00

Ps ducted options quoted

We have selected the following as requested:

Option 1, Panasonic S/U-100 inverter ducted system.
Capable of 10.0kW of cooling & 11.2kW of heating. $ 12,160.00

Option 2, Daikin FDMA100 inverter ducted system.
Capable of 10.0kW of cooling & 11.2kW of heating. $ 12,755.00

Option 3, Panasonic S/U-125 inverter ducted system.
Capable of 12.5kW of cooling & 14.0kW of heating. $ 12,695.00

Option 4, Daikin FDMA125 inverter ducted system.
Capable of 12.5kW of cooling & 14.0kW of heating. $ 13,265.00

Note we have allowed for five circular supply grills and one filtered rectangular return air grill in the hall.
The doors will need to be left slightly open or undercut if we only have one return air grill in the hall.
A vent can be put in the bathroom for an additional $ 450.00.
Fresh air system per ducted system.
We can fit a filter and damper to the systems above to create positive pressure in the house for $ 295.00. We could also fit a fresh air filter, thermostat and motorised damper to the system for $ 790.00 which would then open the air inlet into the home when the ceiling space is higher than the thermostat set temperature and switch off when the ceiling space is to cold. We could also fit a heat recovery ventilation system to the ducted system for an additional $ 3,350.00.

timmmay

20581 posts

Uber Geek

Trusted

Lifetime subscriber

#2746318 18-Jul-2021 20:35

Whatever you do, do not buy Panasonic. They're really loud, budget units IMHO.
Circular supply grills keep the hot air up at the ceiling. You want the MDO square ones on this page. I had the Holyoake "Eco Automatic Round Ceiling Diffuser" to start with. If you open up the little holes to push air down they're quite loud and not much air goes down. If you close them they're no better than the standard ones. I have five in my shed I will sell at some point, I had them removed for the MDO ones which are much better.
Undercut doors needs 1-2cm to get good airflow. Instead I imported these wall vents from the USA. They let very little light or sound through, but let air through fine.
Do not pull air in from the ceiling space. It can get pretty filthy in a ceiling, mice and rats can get in.
Like I said earlier, a big ducted system without zoning will end up in summer with your north facing rooms really hot and your south facing rooms about right. I would NOT do ducted without zoning. I suggest you look carefully into the Daikin zoning system, though I'm not sure if it's great. The Airtouch 4 is good, not perfect, but a lot better than nothing.

I would go with split system for better control. Whether they all run off one outdoor unit or one split with some standalone ask your installed. Ideally with split I would want the units in the ceiling with diffusers into the room, but not sure if that's an option, other than the Daikin VRV which is great but insanely expensive - I was quoted $22K for four rooms.

I'll tell you the problems I'm having with my ducted system - pretty minor:

The Airtouch spill zone keeps overheating 2-4 degrees higher than we set it, overheating the lounge. We may have to get another zone added to dump the heat somewhere else. The spill is when the bedrooms need a bit of heat but not much, more than the minimum the heat pump can provide.
When the system is up to heat there's a cool breeze from the diffusers, pumping room temp air through but it goes through the ducts in the cold ceiling. I actually turn the ducted system off sometimes because I find it so annoying or wear a jumper inside. I'm trying to get the installer / Daikin to work out how to disable this.