Using furnace exhaust to heat greenhouse?

[Brian Noy]

This summer I moved into a house on the south end of a Minneapolis
lot, and was thinking of making a lean-to, quarter hoop green house on
the south side. That part of the yard allows for a 10 x 50 foot
garden, and I think that I can make a hoop house over the entire
growing space. Something that looks sort of like this:
http://www.igcusa.com/Hobby/bc/Cross-Co-Lean-To-Curv-420.jpg

Are there any similar examples locally?
Can I pipe in my furnace exhaust to heat it? I have fairly efficient
boilers, which I'm told will have low levels of CO and be relatively a
clean CO2 source. I can't find any examples of this.
It will be quite visible, so I'll probably have to figure out how the
city deals with this. Any knowledge of permits on a temporary
structure like this?

Thanks - glad to be new on this list!

[Carol Ford]

Do you want to be growing in there for as much of the winter as possible? Ideally, you'd have an entrance to the greenhouse from the house, if you're using the lean-to design. That way, you're not introducing the harsh outdoor temps every time you go in or out of the structure. Alternatively, you could build a sort of shed entrance at the door, which would buffer the outdoor elements, reduce the chances of introducing bugs, and give you a space to store tools and other stuff. Also, if permitting allows, look into the cost of trenching around your greenhouse and putting in stiff blue foam insulation at least 3 feet (reperabbly 4) deep all around the structure to impede frost entry from the soil so it's a heat retainer rather than a heat sink.

Carol

Garden Goddess Produce

Carol Ford

Office Goddess

Division of Sci & Math

Univ. of MN, Morris

for...@morris.umn.edu

"Unless someone like you cares a whole awful lot,

nothing is going to get better, it's not."

       -The Lorax, by Dr. Suess

[Nilgün Tuna]

As an architect, I can tell you that building and fire codes are pretty
strict about furnace exhaust exiting from a chimney placed a minimum
distance from your roof. No matter how efficient your furnace, it is
foolhardy to run exhaust directly into your greenhouse, especially one next
to your house where fumes could leak inside, because carbon dioxide and
carbon monoxide are the products of any kind of combustion.

There are many ingenious ways you can capture heat from other sources and
insulate to prevent its loss. You can use a compost or manure pile in or
around the greenhouse to provide supplemental heat. You could paint the
house wall adjacent to the greenhouse black to absorb heat from the sun,
insulate beneath and around the greenhouse, and build coldframes on the
south side which would provide flexibility and further heat gain. If your
door is outside, try installing the plastic strips found in commercial food
coolers which minimize heat loss or gain.

Nilgun Tuna
Ramsey County Master Gardener