Ducted gas heating to heat pump?

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olivernz

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#303780 8-Mar-2023 22:27

Hi all,

We have relatively new ducted gas heating (and hot water) in the house we bought. Loved it last winter. We also have solar on the roof. I am a bit nervous about gas prices and am wondering if I should upgrade to a heat pump also so that I can use my solar rather than export it. At the moment I pay 7c/kw for gas. I calculated it roughly and consumption wise it's probably a break raven with gas and heat pump running cost wise. But if prices go up ... (and there's also the environmental factor)

Another thought I had was additionally installing a high wall standard heat pump in the hallway. That would heat the bedrooms and the intake for the gas heating is there too. So during the day that could complement the gas heating and I could lower the gas consumption.

Anyone done this? Any tips/expected costs/anything to look out for?

Thanks!
Oliver

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#3047768 9-Mar-2023 00:17

If you lower your gas usage too much, the daily connection charge will still be there and will cost far too much.

Longer term I think everyone on gas will be needing to change to something else, simply because we have to shut down all fossil fuel use worldwide if we are not going to completely wreck the planet. But at the moment, the gas prices are still ok and that leaves people like us in a quandary (we have gas hot water only). We really should change to something else now, but it will be expensive to do and may not work as well. In your case, if the ducting could be reused for a central heat pump system, that might be the best idea. And heat pump hot water systems are available too, but whether they will physically fit where a gas hot water tank was is not guaranteed.

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Senecio

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#3047822 9-Mar-2023 04:33

I would advise against the high wall heat pump in the hallway. It never works how people expect it to to heat the bedrooms off it. You simply end up with a hot hallway and cold bedrooms.

jonathan18

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#3047875 9-Mar-2023 08:13

Senecio: I would advise against the high wall heat pump in the hallway. It never works how people expect it to to heat the bedrooms off it. You simply end up with a hot hallway and cold bedrooms.

Totally agree. We tried this and it was a complete waste of money.

When you say 'ducted gas heating', is there any possibility of switching this to a ducted heatpump, ie re-purposing the ducts and vents? My in-laws did this when their gas ducted system broke down and it worked really well.

timmmay

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#3047876 9-Mar-2023 08:16

If you have a fairly new gas system, personally I would keep using that until it became uneconomic / unreliable. No point throwing something away that works well.

olivernz

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#3047884 9-Mar-2023 08:51

Thanks for the answers. That is helpful.

I am sure the ducting is reusable. I am used to heat pumps in my previous house and -for lack of words to describe it- gas has definitely got the nicer heat. But as said I don't want to use fossil fuels really. And the downside of gas is no cooling. Just fouling the gas heating and not the water means I still pay those idiotic daily charges.

Thanks

Geektastic

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#3047888 9-Mar-2023 09:06

Never had gas here but we did have a ducted heat pump system in our last place. It was excellent. Kept the house at 18 all summer and winter long.

Highly recommended. We’re on diesel fired central heating down here which is nice in winter but no use at all in summer. We cooked.

The heat pump we’ve been waiting 6 months for is finally on the water from Japan, due 15 April, so at least next summer won’t be so unpleasantly hot.

billgates

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#3047952 9-Mar-2023 10:43

We are in the same boat. We have ducted aircon with Solar PV, induction cooktop at least already. The mains gas connection is only there for the hot water. My goal is to divert as much Solar excess going to grid towards self-consumption. I want to go down the route of hot water cylinder eventually as gas prices are currently very cheap, but they will jump. We built our home 2 years ago and spent around $6k on internal gas piping and gas califont incl couple of wall controllers so trying to maximize their return as much as we can before jumping to hot water cylinder. I dont know what we could place in front of our wall tile in bathrooms where the current hot water controllers are located which will need to be removed once gas califont disappears.

I looked into heat pump hot water cylinder, but the good stuff costs close to $10k incl install for a 300l. cylinder which I don't think enough for us with 2 very young kids who love their baths. I am thinking a 500L or 600L cylinder on its own or with a thermal storage system that has the option to connect to a heatpump later on if required but initially run it off couple of 3.6kW elements.

Do whatever you want to do man.

FineWine

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#3048009 9-Mar-2023 10:58

Do Ducted Heat Pump systems prevent "Crying Windows" ??

In other words can they also act as a Positive Pressure Ventilation system ??

Whilst the difficult we can do immediately, the impossible takes a bit longer. However, miracles you will have to wait for.

billgates

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#3048012 9-Mar-2023 11:07

No, ducted heat pumps do not prevent crying windows. In winters, we have to keep the Lossnay ventilation system running along with the heatpump to prevent crying double glazed windows.

Do whatever you want to do man.

olivernz

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#3048018 9-Mar-2023 11:19

Ours didn't cry last winter with the gas heating. Because not thermally broken aluminium there is a bit of crying on those when it gets really cold. If your house is good enough a heat recovery system is excellent.

@billgates: At the moment the stiebel-eltron 300L heat pump unit is probably the best around. Last time I looked it was $4000. I'd be VERY surprised if you need more than 300L. That is a heck of a lot of water! When we had our kids we had 180L and were still mostly fine. There's also some cool systems that take the heat out of the roof cavity to feed it into heat pump. But at the moment we have a infinity gas thing and in summer (no heating) the gas for hot water costs us <$20/month. There's no way I can compete with electricity there at the moment.

From the above I think I am going to go with the 1st idea I had and that is put a supplementary heat pump in the lounge. Then use excess electricity from solar to heat up the house and switch to gas for the night when the sun is down (and heat pumps get less efficient).

Cheers oliver

Geektastic

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#3048044 9-Mar-2023 12:13

FineWine:

Do Ducted Heat Pump systems prevent "Crying Windows" ??

In other words can they also act as a Positive Pressure Ventilation system ??

That depends on the windows.

We had high spec argon filled etc double glazing with sizeable gaps and thermally broken frames.

I tend to run air conditioning rather than heating at night (neither I or Mrs Geektastic are keen on hot bedrooms) and we have never had that issue.

I have had condensation OUTSIDE on the window during the day when it has been very humid and I have the had the chiller on for long enough to cool the window glass enough.

Scott3

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#3048091 9-Mar-2023 14:24

In OP's position, assuming the systems are working well, I would stick with them until they are approaching the end of their useful life.

There is substantial sunk financial and environmental cost in the ducted gas system. (and it is unlikely to have much residual value when removed).

If I was installing a new system I would go heat pump for sure, but No way I could justify spending several thousand dollars (and the environmental cost associated with building a big ducted heat pump, and shipping it across the world), in order to replace a functioning gas system.

On hedging against future gas price increases, Little need to get in ahead with that one. If in 5 years time gas price doubles, you can re-evaluate at that point.

On environmental, while the NZ power grid is about 80% renewable, partially at time's domestic heating is needed, and power demand is high, fossel fuels (gas / coal) are often the marginal unit of consumption. Comparable efficiency to just burn the gas a home at say 80% efficiency, than it is to burn it in a say 30% efficient peaker power plant, run it through a 95% efficient lines system, and then us it in a COP 3.0 heatpump...

solar doesn't line up that well for domestic heating. Firstly heating is only needed in winter, when solar output is lower, and secondly it is partially needed in winter evenings when solar output is zero.

Don't assume the gas ductwork will be suit a heat pump system. Gas systems typically move a fairly low volume of very hot air. Heat pump's for efficiency need to move high volumes of slightly warm air. Currrent ducts could well be to skinny.

Hot water is perhaps a better business case for switching to electric. Suspect the califonts have some resale value on trademe. And a 300L hot water cylidner is cheaper than a 14kW ducted heatpump unit. Also you can get cylidners with duel elements, and set the lower one up on a solar inverter to soak up your excess solar generation. Still I would probably wait for the gas unit to die 7c/kWh is quite cheap for energy, and they only last a decade or two.

FineWine:

Do Ducted Heat Pump systems prevent "Crying Windows" ??

In other words can they also act as a Positive Pressure Ventilation system ??

Depends on the install. Relatively easy / common to integrate one with either balanced pressure or positive pressure ventilation.

billgates

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#3048665 10-Mar-2023 14:46

@olivernz the integrated heat pump hot water units are not that great from longevity point of view. They have been tried and tested. You want a separate compressor and separate hot water cylinder if you want it to last. Servicing integrated heat pump units is also much harder along with replacement if needed. The Steibel unit is also much louder than Reclaim and Sanden both of which have a separate compressor unit. Both these units cost around $10k incl installation. There are couple of folks in Australia who update the comparison chart below of various heat pump units/models that you can view.

Heat pump comparison 3.3.xlsx - Google Sheets

Do whatever you want to do man.

tweake

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#3048763 10-Mar-2023 16:27

FineWine:

Do Ducted Heat Pump systems prevent "Crying Windows" ??

In other words can they also act as a Positive Pressure Ventilation system ??

no. but you can integrate ventilation system to it.

tweake

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#3048764 10-Mar-2023 16:28

Scott3:

Don't assume the gas ductwork will be suit a heat pump system. Gas systems typically move a fairly low volume of very hot air. Heat pump's for efficiency need to move high volumes of slightly warm air. Currrent ducts could well be to skinny.

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