Humidification difficulty

[ddr]

Hello,

My house was built early last year, and this is the first winter I'm in the house. The house has a RUUD RGFG 75K BTU gas furnace and matched A/C. I also have a communicating thermostat (501), which apparently can't control humidifcation function (but can control dehumidification). I also have a bypass humidifier on the furnace, with a manual control.

The trouble I'm having is that the humidifier doesn't seem to help much -- when it runs anytime the system runs it increases humidity levels 2-3% (from 22% RH to 25% RH at 25 deg F outside temp, and 70 deg indoor temp). The furnace is modulating with a variable speed motor, and while it tends to run for longish periods of time, it tends to run at a comfortable 400 CFM (low noise), at 40-50% capacity.

My hunch is that the airflow is too low for bypass humidifier to do much, and thus I'm just wasting water. Should I replace it with a powered humidifier? Do you think it would help resolve the problem?

The house is 3600 sq. ft, and has a second furnace in the attic covering the second floor. Similar problem there, though humidity is more reasonable at 30-33% RH under the same conditions.

Thanks!

[tipsrfine]

How many people living in the home? Just because a house is newly built does not mean it does not have major air leakage. Air leakage in winter allows cold dry air to push its way into the lower leaks in the home, which then pushes the warmer moisture air out of the upper area leaks.

Before looking into the humidifier, I would have your home tested for air leakage.

[ddr]

I'm sure air leakage is a problem in a number of spots, and I intend to do an energy audit, but it's unlikely I'm going to be spending a lot of money at this point on a fix. A fix to humidifier option seems pretty inexpensive and much quicker relative to other options. The house does have rim joists spray foamed, insulated basement walls (R-12), foam sealing around windows and doors, as well as wall outlets and switches on exterior walls. Windows are energy star rated andersen 400 series DH. However, the house wasn't built to energy star standards, so I'm sure there are areas for improvement.

Still would love to hear thoughts on the humidification question.

[tipsrfine]

You just need to figure out whether fixing the air leaks now will be the least expensive option, or whether paying constantly higher heating & cooling bills will end up costing you more.

[Shophound]

You could have excessive duct leakage (assuming ducts are in attic) that is counteracting a lot of the work your humidifier is doing. I would put more focus on a duct leakage test first off since the house itself is pretty new and hopefully tight. Fixing the ducts will improve a lot of things in addition to humidity control in winter.

[second opinion]

A bypass humidifier does not work well on a modulating furnace. The pressure differential between the supply and return, low velocity and lower temperatures at the lower en prevent enough evaporation to do much.

[George2]

I would make sure that water is flowing thru the humidifier. Make sure the humidifier was installed level. Also make sure the damper is open. I assume you can hear the solenoid open and close. Normally we find new home have an excess of humidity from the new construction materials.

[teddy bear]

I would make sure that water is flowing thru the humidifier. Make sure the humidifier was installed level. Also make sure the damper is open. I assume you can hear the solenoid open and close. Normally we find new home have an excess of humidity from the new construction materials.

I fixed a bypass humidifier by install a 6" duct fan in the bypass duct, +200 cfm. I had the windows dripping in two days. You do not get enough air flow from a by pass. Even the standard fan does not have enough. +200 cfm works much better.
Regards TB

[ddr]

Thanks for the suggestions. The issue is with the furnace in the basement, so duct leakage is probably not the major issue -- the basement is insulated and stays at 68 deg. F, and all ducts are sealed up with mastic. The humidifer is level, and water is flowing through it just fine.

Sounds like the problem is air flow is the root of the problem. Short of the 6" fan in the bypass duct (interesting idea), would a switch over to a power humidifier be a reasonable fix?

The overall air sealing is a separate issue, and one I intend to address as well -- I'm having a blower test done after the holidays to see where I stand at the moment. A quick walk through with a thermal imaging camera I borrowed from a friend found a couple of spots, which have been addressed, but everything else looked not too terrible. Fixing the drafts I did find, made no difference to the humidity issue though.

[beenthere]

What brand and model number humidifier do you have.

[ddr]

Not 100% sure, it's a York, but probably relabeled aprilaire 600.

[beenthere]

Not 100% sure, it's a York, but probably relabeled aprilaire 600.

They put a York label humidifier on a new Rheem furnace. LOL

Is it connected to the cold or hot water line.

[ddr]

It's connected to the cold line.

[beenthere]

Hot water would help it output more humidity.

[teddy bear]

Hello,

My house was built early last year, and this is the first winter I'm in the house. The house has a RUUD RGFG 75K BTU gas furnace and matched A/C. I also have a communicating thermostat (501), which apparently can't control humidifcation function (but can control dehumidification). I also have a bypass humidifier on the furnace, with a manual control.

The trouble I'm having is that the humidifier doesn't seem to help much -- when it runs anytime the system runs it increases humidity levels 2-3% (from 22% RH to 25% RH at 25 deg F outside temp, and 70 deg indoor temp). The furnace is modulating with a variable speed motor, and while it tends to run for longish periods of time, it tends to run at a comfortable 400 CFM (low noise), at 40-50% capacity.

My hunch is that the airflow is too low for bypass humidifier to do much, and thus I'm just wasting water. Should I replace it with a powered humidifier? Do you think it would help resolve the problem?

The house is 3600 sq. ft, and has a second furnace in the attic covering the second floor. Similar problem there, though humidity is more reasonable at 30-33% RH under the same conditions.

Thanks!

Assuming that the basement space is equal to 50% of the total home, we have about 42,000 ft^3 of total volume. There is a need for fresh air change to purge indoor pollutants. Most experts consider an air change in 4-5 hours necessary to purge indoor pollutants.
Assuming that during cold windy weather, this home gets adequate fresh air change, expect that you have about 140 cfm of fresh air passing through the home. If the outdoor dew point is <15 ^F and the air leaving the home is 70^F, 25%RH, or a 33^F dew point. The amount of moisture required is <2 lbs. per hour. A couple occupants and a poor functioning humidifier could account for that much moisture. Any less natural air leakage would require mechanical ventilation. Searching for air leaks is not a solution to this problem.
You need to add about 3 lbs. of moisture per hour to maintain 70^F, 40%, a 44^F dew point.

How many occupants are in the home for how many hours? Get the humidifier upto 3-4 lbs. per hour. You can test this concept by adding this much moisture per hour with a hot plate or having 6-8 occupants in the home for 24 hours all doing their thing.
A by pass humidifier with 200 cfm of air should evaporate that much moisture?
Large homes do not have enough occupants to humidify the space.
Also measuring the CO2 levels in the home with a known number of occupants for an extended time can also confirm the air change rate.
One more point. When the outside/inside temps are equal and the winds subside, the natural air change rate declines to near zero. Than 144 cfm of mechanical fresh air is needed to pruge indoor pollutants. When homes are properly ventilated, they need humidification when the outdoor dew points are extremely low. When the outdoor dew points are +60^F, they need dehumidification to maintain <50%RH.
Most do not understand this point. If you only have a couple occupants part time in a large home, you need a good humidifier.
Keep us posted.
Regards TB