I live in very cold winter climate and I am looking for ways to reduce loss of warm air.

One obvious source is the over-the-range microwave vent. As far as I know, the only thing between the range vent and the outside is a chinzy little flapper on the microwave. It flaps in windy weather, which cannot be a good sign.

Is there a better way to seal/damper the vent to allow good flow out, but keep warm air in when not in use? I believe the duct is standard 3-1/4 x 10, which collects to a square (10x10"?) "hood" on the rooftop, and there is nothing else in the vent other than the little flapper.


Along these lines, the bathroom vents let in cold air as well. I assume they have the standard flapper as well, which does some, but not enough.

Specific links to products would be very helpful.

Thank you!

hvac1000

Basically the little flapper is all that is available and here is why.

The units microwave/bath fans etc do not have a powerful enough blower to operate a better sealing device. If you notice you can almost blow open one of the little damper doors with your breath. This is all so designed to allow the manufactures to offer a cheap/reasonable seal without going to more costly dampers and bigger motors. Another reason for not using bigger motors is that they would really waste energy because they would suck just that much more air you already paid to heat to the outdoors.

Are there ways around this?

Yes with the use of a proper make up air unit.
Any air that is exhaust from a home has to be replaced. Bath fans,microwave oven fans, clothes dryers, gas and oil furnaces,fireplaces, Jen Air style indoor grills, and many other appliances remove preheated air from the home and send it outside with your dollars you paid to preheat it with.

The reason you feel cold air flowing back into your home from various pipes/vents etc. is because your home is running on negative pressure and the home is always looking for any hole or opening be it ever so small to draw the air in it just got rid of by all the machines in your home so it can be balanced or have neutral pressure.

For the average person the cost of a air make up unit that really works is to much money and even the simple one I designed for my home still requires the air from the outside to be preheated which costs about as much to do as what is lost to start with. The big difference is comfort and never having to feel a cold draft. I keep my home just a slight bit on the positive pressure side by drawing outside air thru a old oil furnace swing (barometric)damper and then into my return air to be heated. The damper allows for adjustment of the volume from outside and also closes the pipe off when not in use.

There are many parts to this situation and I have only touched on a few. I am sure the net is full of ideas you will just need to search under negative pressure.

pwd77

Thanks, HVAC100, this is good information.

I see your point about the cheap exhaust fans requiring minimal backpressure. And it is true that venting air out requires replacement air.

Clearly you have solved the issue by controlling the pressure and airflow in your house, and I think that is the way to go. I will look for more information on the net.

That said, I think leaky vents are not the way to go. That means there is cold air leaking in 24/7, PLUS the time the vent fans are on. I would prefer the airflow be going full blast for the few minutes a day I need it, then closed off.

I would like to systematically replace the cheap fans with more poweful ones, and and the same time improve the vent control if possible.

Assuming I would like to upgrade my control over the airflow, do you have any other suggestions?

Thanks!

hvac1000

The reason I took the approach that I did was I figured it would be next to impossible to add expensive dampers and motors to all the appliances. So I took the whole house approach.
Other ideas below.

HE100 Air-to-Air Exchanger

Air Exchangers

pwd77

Again, I see your point. I am learning a lot from this! Controlling each vent could get expensive, but I would at least like to price it vs. doing the whole house approach.

Is your "slight positive pressure" actively controlled, or do you something simpler (like a small fan on all the time)?

hvac1000

Actually it has a active control of sorts. It uses a pressure balance sensor from a very old Honeywell damper system. As the air zone would call as in a ((multi zones duct system)) it would speed up the blower to allow the zone to have proper airflow. When the zone was satisfied it would drop the motor down a speed and naturally close the damper for that zone.

This is the kind of system that controls the blower on the main section of the house. It has been modified from Honeywells intent and I hope it never stops working because I will never be able to replace the sensor since it has been long out of production.

I figured that someday I would have to replace this setup so I have done a bit of research. I believe the below item will work for my purposes with modification but hopefully I will never have to change my design for lack of one part (pressure balance sensor)

IAQ Direct - ZoneHandler

pwd77

That looks like a good little device. I hope you never have to use it

I have learned a lot, thanks very much. I could go on and on down some of these tangents, but I shall control myself.

hvac1000

Glad to be of some help.