[hanzosbm]

Hello all,

My wife and I purchased an older home (we believe the initial building was constructed around 1860 with subsequent additions) and have a few issues we'd like to understand/resolve.
The house is about 2300 sqft with 2 floors plus an unfinished half basement/half crawl space. AC/Furnace/Humidifier are in the basement. Throughout the house are a whole number of supplies and returns. Some supplies are along the baseboards in the oldest parts of the house, others are in the walls about a foot off the ground, and in the newest part, we even have a few in the floor. 5 supplies in the basement, 7 supplies on the first floor, 5 supplies supplies on the second floor. Returns: there is what appears to be a non-ducted return in the wall near the ceiling and a large return in the floor on the first floor and another in the floor on second floor. Upstairs, there are two places that are carpeted over that feel like there is a return under them.
The master bedroom (which was the latest addition) has no supplies or returns. Besides that room getting a bit chilly in the winter and toasty in the summer, we've been able to keep the house fairly comfortable by adjusting the dampers on the various supplies.

However, we have a few issues:

1) We love using our fireplace, but we have had to discontinue it due to the smell that arises a day or two following its use. We've had the chimney cleaned and inspected and the chimney company says it is due to negative pressure pulling air down the chimney and into the house. Given the age the house, and general draftiness, it is not well sealed and the smell doesn't correspond to the use of any exhaust fans or such (which we rarely use anyway). My hunch is that in the winter, when we're using it, the large number of supplies in the house are heating things up, pumping warm air upstairs (both directly through the supplies and also through the warm air rising up the stairwell) and creating negative pressure in the family room where the fireplace is located. We had an HVAC company come in to check it out and the kid doing the inspection said it was fine, so we've got 2 companies arguing over it.
2) This is secondary to the smell, but as I mentioned, in our master bedroom, we have no supplies or returns and the temperature in there is always a bit colder in the winter and bit warmer in the summer (I'd say about 5 degrees off the rest of the house. So, tolerable, but not comfortable). Directly below our master bedroom is a half bath that has a dedicated supply that we generally keep closed (because it'll roast/freeze that tiny half bath) in the wall. We are planning to remodel the half bath and I was considering closing off the supply in the half bath and running a duct line up through the wall and essentially move it to our master bedroom. I had some people suggest against it due to the fact that without a return in the room, it wouldn't be very efficient, but I've got to believe it'd be better than nothing, and considering we'd have the walls open anyway, for the cost of 8-10' of ductwork, it seems like a no-brainer, but wanted to get your thoughts.
3) As I mentioned, we THINK there are 2 returns upstairs that have been carpeted over. I'd like to get the thoughts of the experts on whether there is any way to know for sure, and what the likely impact would be of uncovering them. One of them is right in the middle of the hallway, so it's not exactly convenient, but if it helps with our house issues, I'm sure I could find a grate that wouldn't be too uncomfortable to walk over.

I'd really love some help, because frankly, every time we've had an HVAC company out to look at it, the immediately pivot to trying to sell me on a duct cleaning service rather than addressing the issues I called about.

 

[kdean1]

There are several things in the house that contribute to negative pressure - range hood (which should always be used when cooking, esp. with gas appliances), bathroom vents, clothes dryer, etc. Then there is stack effect which is warm air rising and exfiltrating through any leaks in the ceiling and other upper portions of the house, accompanied by infiltration in the lower parts of the house.

You need a blower door test of the house to quantify and locate leaks so you can prioritize the steps to take for a remedy. Ideally, the house should be under a slight positive pressure. A ventilating dehumidifier is a good solution.

Your problem is something that a contractor in the HVAC 2.0 program is equipped to diagnose.

 

[hanzosbm]

There are several things in the house that contribute to negative pressure - range hood (which should always be used when cooking, esp. with gas appliances), bathroom vents, clothes dryer, etc. Then there is stack effect which is warm air rising and exfiltrating through any leaks in the ceiling and other upper portions of the house, accompanied by infiltration in the lower parts of the house.

You need a blower door test of the house to quantify and locate leaks so you can prioritize the steps to take for a remedy. Ideally, the house should be under a slight positive pressure. A ventilating dehumidifier is a good solution.

Your problem is something that a contractor in the HVAC 2.0 program is equipped to diagnose.

Most of the normal culprits I don't feel are a significant cause. We almost never run our hood (electric range and oven). Rarely run our bathroom exhaust vents. The dryer is possible, but the times I notice the smell the most is when I come downstairs in the morning, which tells me it's happening through the night (when the dryer isn't running). Add to the issue that at night is when the HVAC system runs the most, I think it's more stack effect related than anything.

I'll check out the HVAC 2.0 program (hadn't heard of it before). Thank you!

 

[AdrienneGC]

Any time I hear negative pressure, I immediately assume insufficient return is the culprit. Your air handler must receive (have returned to it) the same amount of air it supplies. If it cannot get enough air through the ductwork, it will pull it from cracks, voids, gaps, etc. causing a negative pressure. Definitely focus on ensuring an easy path for returning air to the air handler. You can use a duct size calculator to ensure your returns are adequately sized.

If you feel your existing return ductwork is inadequate, and since it sounds like you have architectural limitations, adding or increasing the size of a central return would be helpful. And make sure any rooms without returns have passive returns (aka, pass-through grilles) and that the doors are undercut to allow air to flow within your home easily.

It is optimal to have a small amount of dry conditioned air push through the building materials to keep them dry. When you have a negative pressure situation, you are bringing unconditioned, possibly moist, air through the building materials into the building. It's a bad situation all around. After you have ensured your returns are adequate, you could also consider adding a fresh air duct to your return at the rate of:

0.01 x Area [SF] + 7.5 x (number of bedrooms +1)​

Good luck!

 

[kdean1]

Any time I hear negative pressure, I immediately assume insufficient return is the culprit. Your air handler must receive (have returned to it) the same amount of air it supplies. If it cannot get enough air through the ductwork, it will pull it from cracks, voids, gaps, etc. causing a negative pressure. Definitely focus on ensuring an easy path for returning air to the air handler. You can use a duct size calculator to ensure your returns are adequately sized.

If you feel your existing return ductwork is inadequate, and since it sounds like you have architectural limitations, adding or increasing the size of a central return would be helpful. And make sure any rooms without returns have passive returns (aka, pass-through grilles) and that the doors are undercut to allow air to flow within your home easily.

It is optimal to have a small amount of dry conditioned air push through the building materials to keep them dry. When you have a negative pressure situation, you are bringing unconditioned, possibly moist, air through the building materials into the building. It's a bad situation all around. After you have ensured your returns are adequate, you could also consider adding a fresh air duct to your return at the rate of:

0.01 x Area [SF] + 7.5 x (number of bedrooms +1)​

Good luck!

Good points.
OP, are any of your ducts in an attic or crawlspace? Supply leaks outside the envelope will put the house under negative pressure.
There are tests which can measure the amount of air coming out or going into your grilles and registers. An imbalance would indicate duct leaks or bad design.
Other tests such as Trueflow grid or duct blaster may be called for to track down what’s the matter.

 

[pecmsg]

Have a blower door test performed.
Have the TESP tested on the ducts.
Make corrections where need and add a while house dehumidifier with outside air connections to make the house slightly positive.

 

[ksefan]

With a home of that age, with several additions, it might be near impossible to fix the duct system without starting over from scratch. As mentioned, a blower door test, and maybe a flow hood to provide an assessment of the airflow and duct leakage.

 

[samgevas]

Play bob marley music. I find that increases the positive vibes...

 

[hanzosbm]

Good points.
OP, are any of your ducts in an attic or crawlspace? Supply leaks outside the envelope will put the house under negative pressure.
There are tests which can measure the amount of air coming out or going into your grilles and registers. An imbalance would indicate duct leaks or bad design.
Other tests such as Trueflow grid or duct blaster may be called for to track down what’s the matter.

Crawlspace, yes. Attic, no. The good news is that the crawlspace is insulated and sealed off as well as a crawlspace can be. As for the ducting, it's not sealed, like...at all. No mastic, no tape, nothing. So I have no doubt it's leaking everywhere, and I don't think I'll be able to correct that. What I'm really hoping is that, A) I can get someone in to determine if I'm correct about the pressure imbalance (I had a company come once and the guy claimed it wasn't under negative pressure, but he simply held the instrument in his hand in a single room without comparing it to the outside or any other room/floor, so I'm doubtful), and B) if there is, what is the likelihood that exposing the air returns upstairs could help to alleviate it.

 

[kdean1]

A service called Aeroseal can seal ductwork without access to the ducts. HOWEVER, sealing the ducts may increase static pressure to an unacceptably high level.
Testing pressure without respect to the outdoors is wrong. Fire that guy.
Measuring static pressures will indicate which portion of the system is restricted. Then efforts can be focused on that part first. Undersized/returns are a common problem. Un-ducted returns are another frequent culprit.