Water heaters/boilers. Why inside the house?

Probably not worth a new topic, but I've been wondering for a while.

We use pretty similar stuff in Japan, but the boilers go outside the house.  Even when we rented apartments, they were outside.  (Except for older systems with cranks.  Those were inside the bathtub units.)

An interesting question.

You'll find some houses where the boiler is located either in an attached garage, or a utility area which is accessible only via an outside door, but inside is by far the norm in most homes. 

There's quite possibly a strong element of "That how's we do it traditionally" involved.  As to why that's how we've done it in the past, there's probably room for conjecture.

Indoor boilers are less likely to freeze up if shut off and left unattended in winter while the owner is away.  Outside boilers would almost certainly need to be left running or drained down to avoid problems in frosty weather.

The traditional indirect hot-water system generally tries to place the hot cylinder as close as possible to the points of use, then the boiler is located for easy connection to the cylinder.  The closer the two are the easier it is to get circulation without having to resort to extra pumps.  In a typical older-style two-story house, that quite likely means the cylinder somewhere outside the bathroom and the boiler in the kitchen below.

There's probably also the point that in a warmer country you want hot water but don't need heating for much of the year and placing the boiler outside reduces the excess heat indoors.  In a climate like Britain's, most of the year the extra heat given off by an indoor boiler is actually welcome,  and would be wasted outside.   Again, from the traditional point of view, remember that 50 to 60 years ago winters here tended to be quite a bit colder than they are today.

That makes some sense, thanks!

We do have to keep the boiler running when it gets below zero.  My MIL usually calls to warn us of cold snaps.  It needs re-starting after moderate earthquakes, but the gas does, too, and they're all outside the kitchen.   I like it being outside, though... no ugly box to cover up or make room for in tight spaces!

Another thing, possibly...

boilers are very expensive!
you wouldnt leave an expensive piece of kit outside to be stolen or vandalised, in most cases.

the first house i bought in the UK was a 110-year old house that was newly refurbished.  The builders would not install the new boiler till the morning we moved in, because they didnt want it to be stolen from the empty house.