Why Does Steam Heat dry out the air More than fin tube elements??

Alx

Can anybody explain why, in my current home that utilizes steam radiators,   the steam radiators dry out the air more  than my previous home where I had fin tube elements. I noticed the air feels drier.

Charlie from wmass

first off I do not notice this but it could be

due to the higher surface temperature of the radiators.

Canucker

What is the

difference in construction between the 2 houses? Old houses tend to have steam systems installed, and unless you have done some upgrading to the building envelope, you are letting air in during the heating season that has a lower humidity than the other months. The rads just heat the air that is there, whether its damp or dry.

ChrisJ

Air leaks

No heat actually drys the air more or less than others.  When you look at the humidity level in the air its typically listed as RH or relative humidity.  This is because the warmer the air, the more moisture it can hold.  If you take 30F air with say 50%RH and warm it up to 70F that RH number will drop, substantially.  There is a way to calculate it but I do not know how.  A good example of this is when the windshield in your car fogs up from you breathing in the vehicle first thing on a cold morning.  Your moist warm breath hits the cold glass and the air near the glass cools rapidly and cannot hold as much moisture anymore so it condenses on the cold glass.



Whether you use steam, hot water, forced hot air or a nuclear reactor you will have the same exact results.  Forced hot air may seem drier because of the air movement.



The only reason you could notice a difference between the two homes is as Canucker said, air leaks.   When you leak cold air in you are heating that air and ended up with must drier air in the home.  Where if you do not have many leaks you will retain a lot more from showers, cooking and even people breathing. 



Here is a good article on relative humidity.  http://en.wikipedia.org/wiki/Relative_humidity

nicholas bonham-carter

Dry air from steam heating

One point to consider is the system pressure. If it is too high, then the surface temperature of the radiators will be higher, contributing not only to dryness, but also to the bank account of the fuel supplier!--NBC

Hap_Hazzard

It doesn't.

The type of radiation makes no difference. Neither does the transport medium (i.e. steam vs. water).



Indoor air is dry during heating system because you're taking cold air, which has low moisture capacity, and heating it up, which greatly increases its moisture-carrying ability--in other words, dropping the relative humidity. This makes the air suck up any moisture it can find, leaving everything it contacts parched.



One thing that will contribute to this is excessive amounts of cold, outside air moving into the house. Atmospheric boilers, whether steam or hot water, move large amounts of air up the stack during combustion--usually a lot more than is needed for efficient combustion and removal of exhaust gases. Unless there is a fresh air duct piped into the boiler room, this draws air into the house through any crack it can find.



Sealing up the cracks doesn't really help. It might slow it down a little, but if the air is being forced out, it has to be replaced. It's going to find its way in somehow. If it didn't you'd be living in a vacuum. More importantly, it could actually prevent the exhaust gases from being vented.



The first thing to do is, if your boiler doesn't already have a vent damper, get one. I just put one on my boiler this winter and it made a huge difference. It doesn't prevent air from going up the stack during combustion, but it keeps all the warm air in my basement from leaking out while the burner is off.



You can also install a fresh air duct to bring air directly into the boiler room so it doesn't have to go through your living space en route. I don't know all the details yet, and those details are critical, so you might want to start a thread on either the Gas Heat or Oil Heat forum, depending on what you have, or on the Indoor Air Quality forum.