Best heating system for 1975 house?

The tenant of my Sebastopol house has somehow managed to run up an electricity bill of $4000 (!) which he blames on the fact that the house has electric h.w. and electric underfloor heating in the slab (the sort of thing that was popular in the UK in the 1960s when we were told that nuclear power would be so cheap they'd all but give it away) and has asked I'd consder installing something more affordable

I'm perfectly open to this as long as I get around 10% return - say 5% return on capital and 5% to allow for the system needing to be replaced down the line. If cost was secondary (i.e. assuming the tenant would pay more for something better) what would forum members suggest? It's a better than average 4-bed house built 1975 so probably no wall insulation. The house doesn't have gas currently - don't know whether it's in the road.
Seriously 4000dollars? And it not even winter yet?

Buy them a blanket, socks and a jumper...

I know i live in qld, but really..... $4000 :confused:
Two things to address
1) Roof/Wall Insulation, curtains, shading of windows, sealing of air leaks around windows/doors, underfloor insulation (if timber framed).
2) Have the electrical system checked out - is the meter on the fritz?

On another note, why isn't the hws on off-peak (or other tarriff), is the underfloor heating thermostat working?

Nothing you do in the way of environmental benefits will give you a return (only reduce the tenant's running costs - happy tenant/happy landlord, less vacancies/instant return). However, if you install insulation (everywhere) and put in an ac unit or two, then you may be able to get a higher rent.
Definitely an inverter reverse cycle split system.

Maybe one in the living area and small one in master bedroom. Make sure you go for a good brand, like Fujitsu, Mitsubishi electric or Panasonic for efficiency ,performance and future parts availability. It's also the safest form of heating in less risk of fire.

Did you know that high quality inverter is up to 4 times more efficient than conventional electric heating and twice that of gas.

It's also cheaper than wood if you have to buy the wood in.

Eg, Fujitsu 8 kw split can put out upto 11 kw of heat while consuming approx 2.6kw of power.

In some of the rental properties we install into the owner usually get 10 to 20 a week more rent, while the equipment is written down. Also some of the property managers i deal with tell us the houses with ac fitted also rent easier if there is some vacant competition around the same area.

Hope this helps.
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Thanks for the replies. Met a heating guy at the property today who reckoned that ducted warm air heating and instantaneous gas HW was the way to go. Good news: (i) the utility company will bring in gas from the street for free; (ii) replacing electric tank HW with gas qualifies for a grant; (iii) replacing electric underfloor with gas qualifies for a grant. Waiting for the quote and to find out how much the grants are but looks promising.
Now the work has been done, a quick update which might be of interest to anyone in a similar position. Getting gas brought in from the street cost nothing! Getting the slab heating replaced with warm air (unit in ceiling, ten outlets) and an instantaneous water heater to replace the electrically heated cylinder cost me just $1900 after grants. Am more than happy and so are my tenants.