Whats a Heat Loss Survey?

Whats a Heat Loss Survey?
A heat loss survey is primarily used in hot water heat applications to determine what amount of radiation is needed for a particular room, and also how big of a boiler is required for the house. It can be used in steam heating also, but only for determining the size and quantity of the radiators. In steam heating applications the heat loss survey has no bearing at all on the size of the boiler.
It works like this- we go around the house and gather up data. We measure the floor area, the wall area, are the walls insulated? how thick are they? whats the construction of these boundaries? are there any fireplaces? do they have dampers in the flue? are there doors on them? what are the windows like? single pane, double pane, etc. We gather up all this type of data then feed it into a computer that in turn tells us the heat loss in btu's per hour on the design temperature day (a day that your warmer than, 97.5% of the time). This information is then used to determine how much heat emitter (radiator) you need to put in each room. The total heat loss figure is then used to accurately size the boiler. So unless a heat loss survey is done, any installation will have been by guess rather than engineering.