# Why is a boiler furnace called a boiler furnace?
**URL:** https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865
**Category:** Factual Questions
**Created:** [December 8, 2015, 10:22pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865 "2015-12-08T22:22:28Z")
**Posts on this page:** 16
**Page:** 1
### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [December 8, 2015, 10:22pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/1 "2015-12-08T22:22:28Z")
I have a baseboard water heat system, and around here at least, that type of furnace is called a boiler furnace. This seems odd to me, since the name “boiler” seems to imply that it boils and makes steam, which it doesn’t do.
Why are these types of furnaces called boiler furnaces? Is it just a generic thing dating back to the steam furnace days?
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### Author:  [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)
#### Post date: [December 8, 2015, 10:57pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/2 "2015-12-08T22:57:24Z")
If it circulates water around your house it has some kind of ‘boiler’ to heat up the water/fluid that it uses. It’s using the word boiler in the most general sense of the word.
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### Author:  [@davida03801](https://boards.straightdope.com/u/davida03801)
#### Post date: [December 8, 2015, 11:57pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/3 "2015-12-08T23:57:02Z")
A boiler heats water. A furnace heats air. There is not such thing as a boiler furnace. It is either a boiler or a furnace.
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### Author:  [@bob\_2](https://boards.straightdope.com/u/bob_2)
#### Post date: [December 9, 2015, 12:00am UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/4 "2015-12-09T00:00:28Z")
Could it circulate hot air as well as producing hot water for showers etc?
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### Author:  [@NBYodo](https://boards.straightdope.com/u/NBYodo)
#### Post date: [December 9, 2015, 1:05am UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/5 "2015-12-09T01:05:25Z")
Potentially, but not that I’ve ever seen.
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [December 9, 2015, 1:17am UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/6 "2015-12-09T01:17:06Z")
> [@bob\_2](#):
>
> Could it circulate hot air as well as producing hot water for showers etc?
I’ve never _personally_ seen it in a residential sense, but the company I work for uses district heating. The powerhouse generates steam which is then piped to all of the buildings within about a square mile. The steam is used both for facility heat (via radiators) and for hot water (via heat exchangers,) but is not temperature controlled so the sinks all have warning labels stating “HOT WATER IS VERY HOT.”
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### Author:  [@Dereknocue67](https://boards.straightdope.com/u/Dereknocue67)
#### Post date: [December 9, 2015, 8:29am UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/7 "2015-12-09T08:29:39Z")
Your system can also be referred to as a hot water system. It can called a boiler furnace because the furnace heats the boiler and they’re two separate components housed together. Similar to a hot air furnace except the furnace heats the air. If you really want to be more descriptive while informing a repair technician about your system, you might say you have either a gas or an oil fired boiler.
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### Author:  [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)
#### Post date: [December 9, 2015, 2:15pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/8 "2015-12-09T14:15:40Z")
> [@davida03801](#):
>
> A boiler heats water. A furnace heats air. There is not such thing as a boiler furnace. It is either a boiler or a furnace.
Needlessly pedantic. A ‘boiler’ always heats water, but a ‘furnace’ can be any device that heats a medium (air or water) by burning something (oil, gas etc.) and circulates it thru a house (via ducts or pipes). The key issue is that a ‘furnace’ is centrally located (basement, crawlspace) and it circulates the heat throughout the house (as opposed to a fireplace). A portable electric heater is just a portable heater, but there are whole-house, forced-air [electric ‘furnaces’](http://www.shop.thefurnaceoutlet.com/20KW-Electric-Furnace-68240-BTUs-MBR1200AA1HKR20C.htm?gclid=CPLsrPz6zskCFQoqHwodvWgFGg), they’re just not too common because electricity is usually more expensive than gas or oil to use to heat a home.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [December 9, 2015, 2:38pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/9 "2015-12-09T14:38:04Z")
Unconfirmed, but I have been told that early hot water systems used the same boilers as steam systems. Having seen some old cast iron hot water boilers it sounds believable.
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### Author:  [@fire\_hazard](https://boards.straightdope.com/u/fire_hazard)
#### Post date: [December 9, 2015, 5:47pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/10 "2015-12-09T17:47:57Z")
The term “boiler” is in use since the early days of hydronic heating.
Although a modern steam boiler is significantly more complex than one where the temperature is kept below boiling point, they share the same basic components. So they are called “boilers” even though they are limited from actually boiling.
No cite, but I am professionally qualified in a closely related field for thirty years.
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### Author:  [@md2000](https://boards.straightdope.com/u/md2000)
#### Post date: [December 9, 2015, 6:11pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/11 "2015-12-09T18:11:19Z")
I always thought the big thick cast-iron radiators found in old buildings were for steam heat, not hot water. By the time the steam returned to the boiler, it was warm water. when the system fired up, you could hear the flap valves(?) clanging shut regularly as the heated water/steam condensed and tried to backtrack.
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [December 9, 2015, 6:28pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/12 "2015-12-09T18:28:41Z")
The big cast iron ones usually are for steam.
The ones in my house are small, baseboard radiators, and look like this:
[ ](http://seguinhvac.com/joomla15/images/stories/hydronic_baseboard_heater.jpg)
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### Author:  [@MeanJoe](https://boards.straightdope.com/u/MeanJoe)
#### Post date: [December 9, 2015, 6:35pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/13 "2015-12-09T18:35:41Z")
> [@md2000](#):
>
> I always thought the big thick cast-iron radiators found in old buildings were for steam heat, not hot water. By the time the steam returned to the boiler, it was warm water. when the system fired up, you could hear the flap valves(?) clanging shut regularly as the heated water/steam condensed and tried to backtrack.
I have cast iron radiators and it is hot water that is circulated through the system and not steam. The home’s original boiler was replaced in 2009 with an energy star high efficiency hot water boiler.
As to the OP, I’ve never referred to it as a boiler furnace nor have any of the boiler techs I’ve used for maintenance issues.
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### Author:  [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)
#### Post date: [December 9, 2015, 7:44pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/14 "2015-12-09T19:44:29Z")
> [@TriPolar](#):
>
> Unconfirmed, but I have been told that early hot water systems used the same boilers as steam systems. Having seen some old cast iron hot water boilers it sounds believable.
I have seen the same style Scotch Marine boiler and Horizontal return tube boilers used for steam or hot water heating.
I have never heard any called a boiler furnace. Though a boiler usually does have a furnace as part of it.
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### Author:  [@TheFaerie](https://boards.straightdope.com/u/TheFaerie)
#### Post date: [December 9, 2015, 9:14pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/15 "2015-12-09T21:14:47Z")
It must be a regionalism. They’re referred to as just boilers for the most part. I used to be a HVAC engineering tech and I’ve never heard the term boiler furnace.
And yes, the big cast-iron radiators can either be steam or hot water, and although not nearly as common as in industrial uses, the same boiler can be used to heat water for household use.
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [December 9, 2015, 10:08pm UTC](https://boards.straightdope.com/t/why-is-a-boiler-furnace-called-a-boiler-furnace/739865/16 "2015-12-09T22:08:30Z")
The term is common enough that the manufacturer Weil-McClain has an entry for it in their glossary of terms.
Though to be fair, this is what it says:
> [@](#):
>
> weil-mclain » glossary » boiler furnaces
> Boiler Furnaces
>
> There really is no such thing as a “boiler furnace.” You either have a boiler or a furnace.
>
> With a furnace or warm air system, air is used to conduct heat from the furnace to rooms in the house. Air is warmed as it passes over a heat exchanger, and then blown throughout the house by a motorized blower. Sheet metal ducts channel the heated air to various areas of the house, and the heat enters each room through registers. Boilers, or hydronic heating systems, use heated water to supply heat to the rooms in the house.
>
> Boilers send steam through pipes to steam radiators or hot water through baseboard radiators, radiant floor systems, snowmelt systems or pool heaters. Weil McLain can assist you in choosing the correct boiler or furnace for your home.
It’s apparently not very common. After quite a bit of google searching, I found one message board entry (not the SDMB) where someone called it a boiler furnace, and one web page where the term was used, but it was in quotes to indicate that it wasn’t the proper term (elsewhere on the page it explained the difference between a boiler and a furnace).
Anyway, thanks for all of the answers. I was more curious about the “boiler” part of it since it doesn’t boil, and I learned that the term I’m accustomed to is not only wrong, but not even common.
Ignorance fought.