From: John De Armond
Newsgroups: sci.engr.heat-vent-ac
Subject: Re: Gas Heat is Dry Heat?
Date: Sat, 13 Jan 2001 04:10:46 -0500

Sechler wrote:
>
> > Dry heat or wet heat is a load of BS.
> >
> > In the winter, cold outside air, when heated to room temperature, is BONE
> > DRY.
>
> That I understand.  I'm just curious why gas heat got this reputation (at
> least it has here in NC).  Manufacturer's of home radiant floor systems
> claim their system can maintain a higher RH because a lower space temp can
> be comfortably maintained, infiltration from leaky return ducts is
> eliminated, and a more uniform space temp reduces convective drafts.  This
> makes sense to me.  But the same argument can be made against heat pumps.

Wouldn't be the first time that a mfr had lied in their promotional
materials.

I think I know the source of the myth.  As usual there was a kernel
of truth in the beginning.  It was only AFTER we made the horrible
mistake of replacing our gas furnace with a heat pump several years
ago that I realized the difference.  With combustion heat, the duct
air is much hotter than with a heat pump.  This can cause several
effects.  Being hotter, the RH of the emitting air will be lower
than the air from the same room heated with a heat pump.  This can
cause drying of objects in the near vicinity of the duct, including
humans.  Which segways to the next effect.

I didn't realize it until our conversion but we had the habit of
migrating near a register in order to get warm.  That way we could
warm up without having to actually have the house warmer.  But the
air would dry out our sinuses which would lead one to conclude that
the gas heat is "dry".  Since the air from a heat pump is only
slightly warmer than the room air, one quickly learns that moving
near a duct only makes one colder.  One therefore spends less time
near emitting duct air and more time in the room where the air is
wetter.

I remember the same effect with steam heat when I was a kid.  We'd
huddle around a radiator to keep warm in our drafty old house.  The
air coming off the top of the radiator was hot and dry and would
quickly dry out the sinuses and make everything dry enough to make
tons of static electricity.