Furnace/boiler (and HWH) PLACEMENT

Our current furnace is stupidly placed and eats a lot of important space in our smallish 1200 sq. ft. 1.5 story house. FWIW, we live in the usually mild Pacific NW where it doesn't get very cold, but there is a lot of rainfall (see below). I want to replace a gas-fired forced air furnace (and gas water heater -- see below). Considering various options -- staying with same type of furnace or going with a boiler and radiators, etc. What I'd like to know is what kind of limitations should I be aware of in terms of _placement_ of such units.

Our "utility room" is a walled-in area between the house and the (formerly unattached) garage. It probably has minimal insulation, and is outside the foundation, sitting on a slab of unknown depth/thickness. This area could be used, but is also very small, and contains our washer and dryer as well as an aging gas tank-style water heater that I want to replace as well. Thus, I was interested in addressing both space heating and DHW at once and gaining useable space in the house and, hopefully in the utility room too.

I was wondering if having the replacement unit(s) outside of the heated space (say, in our unheated and uninsulated garage, or in the attic) is a big problem. Due to the rainfall, I was concerned a horizontally-mounted force air furnace in the crawlspace -- a neighbor had theirs damaged by water accumulating there during a deluge a few years ago when power was knocked out (which took out the sump pump).

Do you ever have to worry about freezing? A boiler where it can freeze is a pain. You can run antifreeze in it, but it decreases the efficiency, and you still have problems with an autofill valve or some means of filling it up...that can't be full of antifreeze. A boiler can be quite small - mine hangs on the wall. An indirect WH can normally be smaller than a gas-fired waterheater, since the boiler may be larger than the typical burner on a tank. If you have access to underneath the floor, you could do staple up hydronic verses radiators, and not take up any floor or wall space in the house. In fact, many of the new mod-con boilers can be put in a closet in the living space. They are essentially silent. If I'm more than 3' or so from mine, I can't hear anything, and even standing next to it, I have to listen hard and I can hear it only because I know what to listen to. A mod-con would let you match your limited heating needs better than something that can only run full-bore (which you may need to reheat the water in the indirect WH).

I assume your ductwork is in the attic, so why would you want the air handler in the crawl space. Is the attic high enough for a horizontal unit there. These are used here when a roof top unit is not advisable. As far as placement is concerned, you can install it and the water heater anywhere they will fit, as long as there are no conflicts, such as electical panels, etc.

The ductwork is not in the attic. It runs under the floor, in the crawlspace for the first floor, and runs up the walls for each of the two upstairs rooms (one duct is inside a closet on the first floor, and the other, I do not immediately see -- perhaps it is inside an interior wall).

I want the furnace (and HWH) to be out of the living space because the house is very small and we need all the space we can get. Using the attic or crawlspace each have their own challenges, it seems, so I was wondering about the utility room or the garage.

If you are going to stick with a gas fired forced air furnace, than placing it in the garage should not be a problem. Tying into your existing ductwork and insulating any runs may be the challenge. If you go with one of the high efficiency furnaces in an unheated space you will have to figure out how to get the condensate to a drain, or your garden, without it freezing and blocking the flow.

Baxi Luna boiler/ water heater combo with a hydro coil for ac and heat.