What is a Hot Water Furnace?

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  • Written By: Ken Black
  • Edited By: Bronwyn Harris
  • Last Modified Date: 28 September 2019
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A hot water furnace is a system that heats air through the use of heated water running through pipes and into a radiator. The heat emanating from the radiator warms the air throughout the rest of the room. Thus, the home can be heated just through the use of water. This is one of the most common types of furnaces, especially for older and larger buildings.

The use of the term hot water furnace may be a bit of a mischaracterization. The term furnace usually applies to the heating of the air, which is then circulated throughout a building. However, a boiler heats water. Boilers, especially large ones, require constant attention and may even have someone watching them full time in some operations.

There are advantages to a hot water furnace when compared to other types of furnaces. For example, it is usually more efficient to move hot water than it is to move hot air. This is because water retains its temperature longer than air does. Also, it is easier to direct the water where you need it, more so than air. For example, if a room is not in use, a valve can shut off the water to that room.


As far as types of heaters go, a hot water furnace can also have some disadvantages. It is usually easier to detect a leak or other problem area with this type of furnace. While this may, on the surface, seem like an advantage, it is not. The reason it is easier to detect those problems is because the problems are often very messy and destructive. Also, if there is some sort of power failure and the furnace fails to operate, there is a chance of the water freezing. This could cause a massive problem inside a building if a water pipe were to burst.

There may be some safety disadvantages to a hot water furnace also. The radiators can get quite hot. Accidentally touching them could cause burns and many of the radiators are exposed and can be touched by children and adults. To help prevent this, some find objects to put in front of their radiators. However, if placed too close to the radiator, the object could become damaged if it is sensitive to heat.

While the main use of a hot water furnace is in larger buildings, there are some models that are made for home use. These models are typically not used very often, as most prefer the convenience that comes with an air furnace.


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Post 3

I bet it would be really hard to adapt a hot water furnace so that it could also provide some type of cooling. Having a heat pump would be much simpler. The heat pump is already set up to provide heat in the winter and cool air in the summer. Of course, when you live in a place that doesn't get hot enough to need air conditioning this is not a concern, so maybe a hot water furnace would be ideal in places where the summer temperatures are mild.

Post 2

@Feryll - If you already have a working hot water furnace that is one thing, but I wouldn't advise you to go out and buy one to put in your house. They are more expensive than forced air systems. I have a friend who just told me about the one his parents have in their house. Like this article mentions, when the system springs a leak it can be a major hassle.

My friend's parents were out of town on vacation last winter and my friend went to check on the house for them. We were having really cold weather at that time, and the hot water furnace stopped working for some reason. When this happened the system froze and then when the frozen water thawed there were cracks throughout the system.

The water damage was extensive, and on top of this the boiler had to be replaced, and all of the radiators had to be patched or replaced.

Post 1

Having lived mostly in places that didn't get really cold in the winter for long stretches, I have never had a hot water furnace. However, I have seen pictures of the radiators. Also, I remember visiting my aunt when I was little and she had the radiators in the hallway upstairs. I like the pros this article mentions about using water to heat. How expensive is a hot water furnace system?

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