heat pump question

Need help as I am not to familiar with heat pump systems. unit is installed in a 1983 condo and it has these 4 ducts termination into the attic. One appears to be supplying heat to the unconditioned space I think!! are the others return air ducts or what? I have no idea what I am looking at and need advice. yes there is alot of snow drifts in the attic.


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If this is a Heat Pump, there are no reasons for these pipes in the attic.

Any air discharging into the attic must be made up by drawing unconditioned air from around door and window openings.

Brian, It’s snowing in the attic pics.

I was wondering about the pic’s but when he said “snowdrifts”, I assumed that the snow had already built-up into drifts. I have seen from 12-14 inch high drifts in attics up here…The Great White North!!

Since I’ve owned a blower door and was doing air leakage control contracting way back in 1981, I’ll add a bit of info about the unconditioned air infiltraion in homes:

In an average home only about 10-20% of all the air leakage occurs around windows and doors!!! This is one of the reasons why replacing your windows and doors for energy conservation reasons only has such a long payback of 15-30+ years. Our national audit/grant program for residential energy retrofits reflects this as they only give $30 for each new window while they give about $2000 - $2400 for insulating your attic and walls plus doing airsealing work.

Either way, vents (doesn’t matter what type) should not be venting into the attic space.

I would have turned the heat pump “ON” and went into the attic with my infrared thermometer to see what these vents were.

What are the two flue/vent pipes to? I was not there to see the full pictue but those look like flex duct branches (don’t know how they got them to stand at attention) but the zip ties and the collars make me think they didn’t finish the job. Was there warm air coming out of the ends? Were they even connected at the other ends to the main trunk line? Too much we can’t see to determine what the hey they are or why they are standing in the attic. I can say I’ve never seen this as a part of a normal duct system. Thought at first they might be fart fan ducts but too large.

I would dare to say that this is because it is not the “Window” itself that leaks the most volume but the Framing around the window unit. This, along with all the wall outlets ect., which added up will give a greater volume/area than the average number of windows in the house.

I use the above wording for my clients “better understanding”. They understand windows and doors are wall openings, but don’t grasp the other areas as much.

The concept is that leaking HVAC units to the outdoors causes this sucking effect in the house. Not that windows and doors leak. I also address the potential indoor air issues associated such as Radon and Mold Spore infiltration potential.





Thanks for the links Brian!

There’s some really good illustration there. Good documentation to keep on hand to pass to our clients for their understanding of what we’re trying to detect.

Thanks for splitting hairs on the window/door air infiltration as it brought out some good information. However, we should not forgo considering window and door openings as in your second link the combination leakage of both windows and doors is 21% and the largest single leaker is the walls at 31%. :slight_smile:

We also must consider that this 21% infiltration is on a properly installed/functioning door/window. The attached pictures are from yesterday’s inspection of a knee wall attic/utility room access door. The percentages are way up on this one!

Here’s one for the HVAC duct leakage.

This is a floor air duct that is being utilized as a return. There were about seven of these in the house installed with the same workmanship. You can see all the way down into the crawlspace. These leak on their own that you can imagine the leakage when the 5 ton blower comes on.


Although technically included in the above statement, most people think that there is no air leakage in the interior walls.

Only ever seen foam ones not rubber. In any case, with outlets the biggest reduction is to have something plugged into the outlet. Child proof plugs work well if there is not an appliance to plug in. I recommend the use of both the gaskets and the plugs as using one just redirects the air to the other. Even using both will not totally eliminate the leakage but it is a fast and cost effective solution at air leakage reduction.

Storms are good at breaking the general force of the wind but not for total elimination of air leakage. If unvented, there is the risk of condesation forming between the window and the storm.

Missleading statement. With damper fully closed there will still be some (quite a lot actually) air leakage. Other areas that often have lots of air leakage are the sides of the fireplace where it meets the wall (code requires a gap here but it can be sealed with proper material) and builtin healilators. There should be no reason that these leak if they were built properly but they usually aren’t. Not much you can do about it at this point.

With regards to the pie chart, I would have liked to have see the header or sill broken out from the rest of the ceiling, wall, floor assembly which coveres a fairly broad area.

ok. I’m done now. :slight_smile:


When I went looking for the breakdowns in pie chart form, I kept finding this one repeated and copied over and over. In the 1980’s there were quite a few more research reports with charts that showed slightly varying results but with the same general proportions for locations stated. I probably have some stored away in boxes somewhere…but where???


From my experience, the header in an unwrapped house has quite a bit of air leakage. probably close to that 31%. By the time you take out the doors, windows and electrical outlets out of the walls there isn’t much left except for the header. :slight_smile: Problem is, its one of the most difficult to address without very extensive renovations.

I once told a client who was on electric baseboard and installing electric forced air to expect an increase in thier air leakage. “But why?” they asked “The is no chimeny and all of the ducts will be run inside the house” (meaning no attic duct runs". Then I explained about the air in the joist cavity just waiting for the HVAC to cut a hole for the register boot. Sure enough, their air leakage went up.

Not to drift, but how do you attach a picture to the body of your post like that Paul?

Were joist cavities sealed or did they have to remove some fiberglass insulation to make room for the pipes/boots?


The image is stored elsewhere on the web. In the message box tool bar, click the little yellow box that has two mountian peaks in the background. Then simply enter the url of the image.

Brian, Joist cavities were enclosed cavities but not really “sealed” as you or I might define it. That’s why they leaked. Registers located far enough from the wall as to not need the removal of insulation. With out the air sealing though, the air just filters and/or go around the insulation.

Thanks Paul!

Could those ducts be bathroom exaust fan ducts that never made it through the roof?