Make Up Air for Dryer
Jsmith89
| Posted in General Questions on
We’re in the process of putting together plans for a new build in CZ 4. Our air sealing goal is to be under 1.0 ACH50. We tested a heat pump dryer and weren’t impressed so want to stick with a vented dryer.
What are the best practices for providing make up air for a vented electric clothes dryer?
I was thinking of using a Fantech MUAS750 and just treating the dryer like a small range vent essentially.
We’re using the MUAS1200 for the range hood make up air in the kitchen.
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Replies
Hi Jsmith,
I’m very impressed with the operation and performance of my ventless heat pump drier from LG. For the $850 I paid I think it’s a bargain. Regarding make up air for a conventional dryer I’m wondering if you could fabricate a concentric vent that uses your exhaust to preheat outdoor air and essentially build a condensing dryer vent with a slope to the outside for condensate to exit with airflow. You wouldn’t necessarily have to connect the in coming air to the dryer inlet as long as it was in the vicinity.
I’m really not worried about warming the make up air. We’re in Raleigh, NC. Most of the year it’s going to be hot incoming air anyways and the couple months of the year it’s not the small amount of cold air coming to the laundry room for make up air when the dryer is running will be more than offset by the heat of the dryer.
That seems like overkill seeing that most 27" dryers aren't going to move more than 225CFM. Most are under 150CFM.
Open the window?
I know that's probably not reasonable in this case, but thought I'd throw out the obvious answer first.
No window in the laundry room.
Thinking the alternative would be an 8 or 10 inch duct with filter and a powered damper for passive make up air.
jsmith89,
I'd forgo the powered damper and just have a manually operated air intake.
Even a 1.0 ACH house isn't that tight.
Let's say the house is 3,000 SF, so about 30,000 cubic feet. So one ACH is 30,000 cubic feet per hour or 500 CFM. That's at 50 pascal, so if the dryer moves 150 CFM you'd expect it to depressurize the house 15 pascal.
That's a really minimal amount of pressure. Almost indetectable. The most common way of measuring pressure is by the height of a column of water, that's 3/32". It's the pressure change you'd get from climbing slightly over four feet.
DC,
Our house is 1200sf and n0t extremely tight. When the dryer is running our wood stove backdrafts if we don't open a vent or window.
Our code requires a separate air intake for wood burning.
DC,
Ours too. I was just surprised at how much the dryer depressurized our relatively small house if we didn't provide some make-up air for it.
That said, unless we try to use the wood stove when the dryer is on, what does the depressurization really affect?
Is it possible to send air from the MUAS1200 to the laundry room?
I don't have a window to the laundry room but have a door. I am considering putting on a storm door that has a screen to have window-like functionality (without mosquitos).
That was my plan A but as I dug into it looks like it’d be more trouble than just having a second unit. Basically the sensor it uses to detect how much the range fan is blowing is based on how many amps it pulls. If you put that same sensor on the dryer it would basically make it think the range fan is going full bore when I really need it on extra low. Only way I could come up around it would be two separate controllers for the MUAS fan which Fantech doesn’t sell standalone.
I looked at installing this before going another route. I would use it over the fantech personally, and it would do everything for your house.
https://hvacquick.com/products/residential/Makeup-Air/Residential-Makeup-Air-Fans/AirScape-Residential-Make-up-Air-Unit
I'd like to know what you didn't like about the ventless HP dryer? We have a new LG and while it takes a little longer, it does a great job.
This. I have the Whirlpool ventless and I'm happy with it. Much better than having a hole in the side of my house.
We tested a Miele. The cycles were much longer than typical, if we pulled clothes out when it finished they were good but if you left them in after it ran they would be damp when they cooled like if I started it before bed then take clothes out in the morning.
I wouldn't go crazy on a MUA system. Dedicated MUA is somewhat expensive and probably not necessary for you. Like others have said, a 1 ACH house isn't all that tight. If you have open combustion appliances, then the dryer might be able to induce backdrafting. But in a house that tight, there shouldn't be any open combustion appliances anyhow. If possible, you might be able to try it out and see. Can the kitchen MUA system run at reduced speed, and can it be controlled separately? That could be one solution if necessary. The air would find a way to the laundry room. Even opening a window elsewhere in the house could be an option. If you have a HRV/ERV, they can sometimes be run in a positive pressure configuration to provide just a tad of makeup air. There are lots of possibilities that don't required Dedicated MUA.
Even running two 24" ventless dryers side by side seems like a better solution here. The LG DLHC1455 has a built in condensate pump and will also cook your clothes using 3500W electric heating coils if you're in a hurry. You do need to pack it full or choose the "small load" setting to get things reliably dry but I don't think it takes any longer than our former conventional dryer set to Low heat which most clothes seem to require these days.
I get not wanting a ventless dryer to be the only solution. I have the Whirlpool HP dryer and although I have no complaints about the duration (it is 1:20 per cycle) nor how the clothes come out (I think they are significantly softer, probably due to lack of high heat), the dryer itself is a pain - has a design flaw where lint gets on the coil. There is a LONG thread about that here, and countless websites exploring that issue. Maybe the other brands are better.
So, you want a vented dryer, and you want makeup air. Two potential solutions:
1. Aircycler makes a device called a range relief
https://www.aircycler.com/pages/rangerelief
It consists of a tube you install into the exhaust duct and a device that has a sensor; when the sensor detects air movement in the duct, it sends a low voltage signal to a damper to open the damper. You could install an exterior to interior transfer duct with this damper inline. At the interior side, connect the duct to a boot, put a filter grill on the inside as the "diffuser." Put the sensor tube in the dryer exhaust. When you turn on the dryer, the sensor will tell the damper to open and makeup air will come in through your transfer duct, filtered. It will be unconditioned.
2. Get into smart home automation. Install the same transfer duct with damper as described above, but control the damper via your smart home controls. A Hubitat and a Zen 16 or Zen 17 will control the damper. You just need something to send a signal for when the damper should open & close. Either get a smart dryer that can communicate with Hubitat, or a smart plug for 220 that will tell the Hubitat when the dryer is on.
I just don't agree with the stipulation that a dryer necessarily requires makeup air. I would only begin to entertain it if the house had naturally vented combustion appliances. And even then I'd try to get some measurement of actual depressurization first.
Dc,
I agree. That's exactly our experience. Outside of combustion appliances there is no real problem, and even then maybe not.
I've shared this before, but I have a fairly tight ADU above my garage with forced hot air heat. When the heat is going, the dryer vent opens up. I guess that means I should have make up air for the heat?
Is your heat combustion? Like maybe direct vent gas?
There's nothing magic about make-up air. It's not somehow better than air that leaks into the house through other means. I'm a little puzzled by what you're describing though because I would expect the furnace to depressurize the house, which I would expect to close the dryer damper, not open it.
I have a propane tankless hot water heater (vented outdoors) that supplies an air handler in the garage. This then supplies the hot air to the upstairs apartment, which has a dryer and a propane stove.
I'm guessing the "supply" air for the air handler is simply sucked in through the garage door cracks and crevices.
That doesn't sound efficient at all and is also a code violation. The air handler should be pulling return air out of the conditioned space. If the garage is used for vehicles it should be air sealed from the living space, cars produce all sorts of nasty stuff you don't want in your house.
Makeup air is the least of your problems.
My mistake. The return air and duct for the air handler is in the apartment. The heat in the garage is supplied by the the same tankless hot water heater, but through a Modine radiant heater. It is not connected to any ducting.
It passed building code just fine.
OK, that sounds better. But forced air shouldn't pressurize or depressurize the space, the registers and the returns are in the same space. You'd only see that if you were leaking into unconditioned space. If it's enough to open the damper on the dryer that sounds like the return is pulling from unconditioned space.
Here is another data point. Our house (central NH) is about 4000 sqft of conditioned space, final blower door tested at 0.8 ACH @50 pascals, and with HRV. We also have a woodstove downstairs, with a directly connected outside air duct. The clothes dryer is on the upper level. I can't light the woodstove if the dryer or range hood is running, or I get downdrafting and smoke into the room. However, once I get the woodstove going, the draft up the chimney is sufficient, the outside air duct keeps that going well, and the clothes dryer can be run. I think what happens is that the HRV goes out of balance, with less air being exhausted through it to compensate for the dryer exhaust.