Ventilation - heat exchanger

Hi All,

I have a ventilation question. I am considering installing a
heat exchanger in my shop to aid in ventilating the work area. I
currently have a large hood over the casting and plating area
with a very substantial blower, also I have a dust collector
attached to our polishing stations. My concern is the area where
I have six benches and six bench people, about 800 square feet.
There seems at times to be a cloud of fine particulate emery and
polishing matter floating in the air in this area, sometimes you
can taste it. We all know how dusty a shop can be, you can’t
always open the windows, and it can’t be good to breath this all
the time. I am considering installing a heat exchanger in attic
above this area to suck out the bad air and pump in fresh,
heated or cooled air. The literature that I have read about
ventilating only seems to suggest installing a blower to suck out
the bad air and a fan to blow in clean outside air. The problem
with that is I would need to double the size of my air
conditioning and heating capacity in order to replace the lost
cool or warm air. The heat exchanger will heat or cool the fresh
air to 80% of the temperature of the exhausted air. This seems
like the best solution to me. I am wondering if any of you fine
folks have used or considered a better solution. I will be doing
this for the rest of my life and I would prefer that all of us
breath air as clean as possible.

I appreciate any input,
Mark P.

    I am considering installing a heat exchanger in my shop to
aid in ventilating the work area. .....etc 

G’day Mark Park; I used to work in the chemistry labs of a
University, and the solution there was to recycle most of the air
through filters (and a washing system) to remove noxious gases
and vapours, then to replace the lost or gained heat via a heat
pump. The heat pump is the most cost efficient method of heating
an area anyway; I have one installed in my house which cools in
high summer and heats in mid winter, when needed. In our case, I
get 5+ Kw of heat for the expenditure of 2.9 Kw of electricity.
No - we haven’t abrogated Newton’s First Law of Thermodynamics
(There Ain’t No Such Thing As A Free Lunch). The 2.9 Kw of power
is used only to pump heat from one place to another. It is
reasonably quiet and It also de humidifies the air. If you
simply installed a decent filter between the outflow from the
room into the heat pump (and cleaned it frequently!) you
shouldn’t need really expensive gear. Our very efficient heat
pump cost us NZ$5000 including installation That would be around
US$2500 - 3000 and I don’t doubt that the units are cheaper in
the US anyway. Everything here is pretty dear. We’ve had it 3
years now with no problems and wouldn’t be without it. We didn’t
remove our wood burner stove, but don’t have to use it much as we
get very few power outages. We can easily cook or just as easily
freeze the whole place! Try talking to some friendly heating
and ventilation companies. Cheers,

       / /
      / /
     / /__|\
    (_______)    In temperate Mapua NZ

Hi Mark, Here are a couple ideas you might be able to use.

  1. enclose your oven from the floor to the hood and leave an
    opening for the oven door and an access entry area incase you
    need to service the oven.

  2. you could have an opening going to the outside from inside
    the enclosed oven space. In this manner, you will be drawing air
    from outside the building into the oven area/ chamber and back
    out your exhaust hood. This is even more important if it is a gas
    oven . the opening should be closer to the floor so that all draw
    goes up towards the exhaust and out of the bldg.

  3. If it is a reasonably large oven, you can run some large
    stainless or galvanized duct work through the top area … above
    the oven … and with a small blower , get forced warm air heat
    (free ) during the colder months. Make sure that no fumes can be
    sucked in to the heating system that has just been done. turn the
    small blowers off in the summer months or you will have the
    proverbial " Sweat shop". I designed a system like this for a
    company that had 3 gas fired ovens and we piped the heat all
    over the building and eliminated their heating bill entirely .
    Just the pilot light alone keeps those ovens at 150 oF… If
    you use this idea, you may need to seperate your hood ( you
    mentioned plating is under it as well)Having enclosed the oven
    will also save you a lot of money in airconditioning bills.

As far as polishing hoods and dust collectors… often a mist of
dust manages to get out the exhaust of the dust collector and
this can be problematic if the collector is inside the room. you
can duct the exhaust outside into a steel drum . if you are using
table top dust collectors they are notoriously bad for
production polishing. I would have to know more info on your dust
collector to offer anymore advice.

hope this helps.
Daniel Grandi

Hi Mark,

I have a negative ion producing machine to clear the air. The
particulates have an electrical charge which is the opposite of
the air molecules. The negative ion producer causes the
particulates to fall out of the air and onto the ground. I use
one in my lab and it works pretty well. For the size of the area
you would need a much larger one or maybe better yet several
smaller units.



Skip Meister
N.R.A. Endowment &
Certified Instructor
in all disciplines
Certified Illinois D.N.R.
Hunter Ed, Instructor


Check out a woodworking tool supply place for overhead dust
collectors. These are designed to remove the very tiny particle
of wood dust from the air so should work well for your situation
(fine wood dust is not very pleasant either). They work using a
mechanical filter element and an electrostatic element as well.
They mount on the ceiling and recirculate the air rather than
discharging it outside. I am not sure if Lee Valley has them in
their on line catalogue ( but they do have
them - including a portable one that you can set beside the
source ($249 Cnd - a lot less US$).

Cameron Speedie
Island Gem and Rock