Air is less dense than water.
What would you like to know about them? I have an e-book here " understanding hot water heating systems" http://www.amazon.com/Understanding-Water-Heating-Systems-ebook/dp/B007IVVK4O Hope that helps.
Solar and tankless
no because its not the water your using its the steam from the water
On March 10, 2009 two solar water heating systems were installed on the roof of the White House.
can a home hot water heating system (radiators) be converted to gas fueled from oil fueled heating meathods?
Hot water heating systems use a boiler to heat water and a circulator pump moves the heated water through some kind of radiation. A thermostat controls the on off function and keeps the area at a set temperature. If you need more I have ebooks on the subject. You can find them by searching "Robert VanNorden" on Amazon.com. or search"hot water heating systems" on Google and my book "Understanding Hot Water Heating Systems" will come up on page 1.
salmon
flying fish
An integrated system for both space and water heating. Heating is accomplished in a condensing heating module having a small hot water storage reservoir to reduce burner cycling during periods of low demand. The space heating system includes a fluid flow loop with a fluid circulating pump for circulating a heat transfer fluid in the loop from the heating module to a remote space heating heat exchanger. The heating module can also supply hot water for service use. The system may be configured either as an open loop system, in which the space heating and water heating subsystem are combined and share common lines, or a closed loop system, in which the space heating subsystem fluid flow loop is isolated from the water heating subsystem.
As the pumped fluid carrying heat form the boiler to the radiators.
The plans for several types of solar water heating systems, It calculates what you are spending on heating water as a function of water .Only mystery is how did he bond the copper pipes to the corrugated metal absorber?
There classified as a space heating technique. A central heating system. Usually employinmg a boiler and remote radiation of one sort or another to heat the space. They can be single zone or multi zone systems and they're pretty efficient.