Recommendations for gravity furnace replacement

[Honky Tonk]

No. The compressor is outside, usually wall mounted. The cooler [[evaporator) is inside with the fan, also usually wall mounted. So its just like a window A/C except that its 'split' into an inside piece and outside piece that doesn't have to sit in the window.

But they usually have several other features. They can reverse, so they can both heat and cool [[heat pump). It is sometimes also possible to have multiple inside units connected to one outside unit. And of course they're great where space is valuable as they don't take up floor space like a furnace. This matters more where they don't have basements, or in upper floor apartments.

These units are very popular in mild climates. Not used so much where it gets really cold. They get less efficient as the outside temperature drops below 45 or so. That's why you don't see them much in Detroit.

Instead of wall mounted, is there one where the drive unit would stand alone, outside, on a concrete slab, kind of like a traditional "central air" type unit? [[but smaller) I like the idea of the additional heat pump feature too. It wouldn't be enough to actually heat the whole place, but could be supplemental when the temperature really drops.

[archfan]

Instead of wall mounted, is there one where the drive unit would stand alone, outside, on a concrete slab, kind of like a traditional "central air" type unit? [[but smaller) I like the idea of the additional heat pump feature too. It wouldn't be enough to actually heat the whole place, but could be supplemental when the temperature really drops.

Another type is a high velocity A/C system like Spacepak or Unico. The compressor sits outside, the evaporator and fan are placed in the attic, and small tubes are run to each room. This works for houses with steam or hot water heat. We have a Spacepak system - one nice feature is our vents are in the ceiling, where the hot air is.

http://www.oldhouseweb.com/how-to-ad...ld-house.shtml

[mwilbert]

Instead of wall mounted, is there one where the drive unit would stand alone, outside, on a concrete slab, kind of like a traditional "central air" type unit? [[but smaller) I like the idea of the additional heat pump feature too. It wouldn't be enough to actually heat the whole place, but could be supplemental when the temperature really drops.

Yes. They can mount the exterior units on a pad instead of on a wall, although in my case they laid down some kind of composite pad rather than pouring cement. I have a Mitsubishi "Mr Slim" model which feeds three interior units from one exterior compressor. It is over 15 years old and it still works quite well without ever having been serviced or even recharged, although that was probably unwise and I am thinking of having them take a look at it this year. I do clean the air filters in the internal units every once in a while. I wouldn't call the system silent because the inside units do have audible fan noise, but there isn't any compressor noise inside the house, and it isn't all that noisy outside. They aren't nearly as loud as a window unit.

As Mr. Mouch pointed out, the heating mode gets less efficient as the outside temp goes down, and I wouldn't buy it as a primary heat source in Detroit, except perhaps if you had a really small house, but you can definitely use it if you need heat during spring and fall, and if something goes wrong with your normal heating system it does provide a backup. There is a problem with using it for both heating and cooling as you want the units high on the wall for cooling, but low on the wall for heating, so you have to prioritize one or the other.