Water in range hood caused by ice
Aknorm
| Posted in Energy, Heating & Insulation on
Last fall I installed a new stainless steel range hood with the exhaust fan outside. Several times during the winter (Alaska winter) I would have water coming out of the grill inside the
House, above the stove. Someone said I should install a thermal break in the pipe and wrap the pipe in insulation. Also I believe the spring for the damper is broken, therefore the damper does not close. Has anyone else come across this problem and how did you resolve it? I live in Anchorage.
Replies
The problem is more often seen in bathroom vent fans, where the vent duct rises into an unheated attic before exiting. Moist air from the house rises or is blown up through the duct, and the water condenses out on the cold ducts, then runs down, back into the house.
yes to all, thermal break just before the damper, replace the spring, and insulate the pipe with proper vapour barier covered pipe insulation. Tape the vb to as close to the ends as possible. I'm assuming you've ruled out ext wind driven snow ..
Warm moist air from the house goes up through the duct. The duct is cold, so the moisture condenses. Where is your damper? Many residential dampers are pretty lame. Is there a damper on the exhaust fan discharge? You said the fan was actually outside the house on the roof? Does the ductwork discharge down or is it just continually going upward?
Insulate the duct is [part of] the answer. If outside, it has to be weather proof insulation. If inside (e.g. in the attic), I dont' think it needs a vapor barrier, as the vapor/moisture is insde the duct, so all you have to do is wrap it w/ e.g. fiberglass.
I might have a tendency to put a goose neck type discharge so there isn't so much thermal stack affect drawing moisture out of the house ... but a good damper would solve this if you can have one (in residential applications you might be able to put a fairly tight fitting damper in ... motorize it and interlock it w/ the fan and you would have maximum control and minimum passive air flow).
Keep in mind that range hood exhaust can be a different animal than simple bathroom exhaust (i.e. grease and such).
More info. I built the house over 30 years ago. I put the exhaust fan outside, on the wall because of the fan noise, but the siding covers the mounting flange-bummer. My wife was tired of the old unit over the range so I changed it to a new stainless steel unit. That's when the icing problem started. Rather than climbing a 30' ladder and removing the siding to replace the broken spring, I thought it might be easier to install a new damper inside the building directly behind the fan. Then install a rubber sleeve as a thermal break and insulate the exhaust pipe ( the area is not heated). I like the idea of a powered damper, but is there a problem mixing water and electricity? Thanks for the good ideas.AkNorm
More info. I built the house over 30 years ago. I put the exhaust fan outside, on the wall because of the fan noise, but the siding covers the mounting flange-bummer. My wife was tired of the old unit over the range so I changed it to a new stainless steel unit. That's when the icing problem started.
Ok, so did you install the damper that came with the new unit, or was no damper included?
Did you add a house humidifier? Adds humidity (duh, I know).
New windows or doors that seal better? Better caulking? New siding with foam or Tyvek? These things slow air exchange and increase indoor humidity.
Do you or the wife cook more often with the shiny new exhaust hood?
Your thermal break needs to be no more combustible than the metal pipe... and it will do no good.
Is there a damper at the motor end that may have become damaged, allowing cold air in?
Your attic piping needs to be insulated on the outside. Use at least R8 insulation.
Insulation only slows the transfer of energy. It does not keep something "cold" or "hot"indefinitely. A loose fitting spring damper at the hood end will still allow warm, moist air from the house into the pipe. The chimney effect pulls air through the hood and into the pipe. The entire metal exhaust pipe interior will eventually approach exterior temperature when the fan is "off", no matter the amount of insulation on it. Moisture condenses, and there is your water. That is why the thermal break is useless.
You need to stop the airflow into the pipe when the fan is off. A lot of air can be drawn into a 10" or 12" pipe with a remote mounted fan.
I bet your old hood had a better damper assembly.
Ideally, you would want a commercial type gasketed and sealed motorized damper assembly with an interlock that turns the exhaust fan on when you turn the switch on the hood (damper motor with a built in end switch). That stuff is expensive, and residential people don't want to spend the money... and architects don't allow the room.
Odds are, you don't have any makeup air for that fan, either.
There are dampers on a shaft through the duct and the motor attached on the outside of the duct ... no issues w/ moisture.
In hind site ... maybe the duct should have sloped outwards?? ... then you end up draining onto your siding?
if you remove siding to service ... put trim around in place so in the future you just have to remove trim. Screw it in place and it is easy to remove.
The other guy made a point about humidity levels in your house. If they are somewhat high, you should be ventilating more.
There may be codes that dictate use of dampers, etc. In commercial applications, this is a big deal. Residential applications are different, but not sure how. A damper seal could be a collection point for grease which is why commercial codes are very restrictive.
"I like the idea of a powered damper, but is there a problem mixing water and electricity?"Done right, no.It is done all the time in clothes washer, diswasher, WH, garabage dispoals, refigerators with ice/water, whirlpool tubs, swiming pools.But done right there should not be any water anyway..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.