On Wed, 17 Mar 2004 10:45:19 -0000, "IMM" wrote:


With electrostatic air filters this is not the case at all.

It is exactly the case. The only advantage of electrostatic
filtering is that it is quiet and by precipitating lightweight
particles it prolongs the life of the particulate filters. It has no
measurable effect on internal airborne dust levels.

I'd really like to find out (a) general opinions on this sort of
system relative to conventional radiators

To achieve equivalent comfort levels you need to operate the house a
degree or two warmer than you would with radiators as there is no
radiant heat.

Totally untrue. The heat emitted from radiators is 90% convection.

I refer you (again) to any book on basic physiology. Some are
available with pictures. "Warm feet, cool head" is very applicable to
achieving comfort in heating - unfortunately warm air heating isn't
very good at providing it.

In the design being discussed the use of ceiling feeds for the hot
air, whilst saving on construction costs, is a significant design
flaw and likely to increase rather than decrease stratification.

In well insulated houses the upstairs rooms tend to
become warmer than the downstairs ones which some people don't like
(most prefer bedrooms to be slightly cooler for the best quality
sleep).

One again untrue. This appears a well designed and installed system. The
upstairs, or any room, can be balanced to reduce air flow.

You can reduce air flow but even in Immyland you can't stop hot air
rising (something you must have noticed).

He finally ripped it all out
and replaced it with underfloor heating (at vast expense). That
installation was quite complex as the house is large but he found the
hot head/cold feet characteristic of air heating to be unacceptable.

This was obviously a bad design/poor installation, etc. certainly not
typical for a two duct good design job.

As you have never seen it, are unqualified in the field and have
little or no experience of these systems yourself I feel it more
likely that the various qualified and experienced engineers and
technicians who installed and investigated it know a bit more about
the subject.

(c) how easy they are to control, ie. can you
easily turn up the temp in individual rooms by adjusting the flow to
that room, and do they respond generally quicker or slower than
radiators?

Over the whole house they are very easy to control, individual room
control isn't quite so easy and depends to some extent upon how the
original airflows were calculated (or, more likely, not calculated at
all - there are many poor installations).

Individual room control is possible by having modulated registers and
variable flow fans

Are those fitted in the house under discussion?

(d) how do they compare to conventional systems in terms
of cost of ownership.

Running costs tend to be slightly higher as you need higher room
temperatures.

Total nonsense. Running costs are slightly lower than rad systems.

Why would this be? The house needs to be hotter - how is this
cheaper?

"The key benefit of radiant heating over warm-air heating is that it
warms people and objects in the building, as well as the building
fabric — not the air in the building. For the same comfort level, the
air temperature can be substantially lower — reducing heat losses."
(http://www.bsee.co.uk/news/fullstory...s_spot_on.html)

" Floor heating is as close to the ideal comfort system as possible.
Warm floors deliver heat closest to the coldest part of the body, the
feet. Room temperature remains at a constant, comfortable level
throughout the room, and falls off near the ceiling, where heat loss
is normally the greatest. In contrast, warm air heating tends to make
the ceiling the warmest part of the room and the floor the coldest,
resulting in the greatest possible energy losses and poorest
comfort....A large part of radiant floor comfort is delivered as
radiation, like sunshine, so the average person can be comfortable at
air temperatures quite a bit below those needed with warm air
heating. These lower temperature settings, if used, can save in
heating cost,"
(http://content.honeywell.com/yourhome/Heating/Heat2.htm)

are but two of very many references to relative comfort levels and
heating costs. Not a single one says that hot air systems save
energy by allowing equivalent comfort at lower temperatures because
it is a physiological impossibility.

Repairs and servicing can be expensive as there is
only one manufacturer,

Most gas forced air units are on the British Gas list.

Pity this one burns oil then.

and those that do have little competition and tend to inflate their
prices.

Any proof of this?

Try asking some of you fellow plumbers.


--
Peter Parry.
http://www.wpp.ltd.uk/