Radiant heat, humidity, & air quality

hobojohnny

hello
we are building a home with radiant heat - not forced air. i understand that radiant heat doesn't suck moisture from the air, but i am still concerned about maintaining a proper humidity level. should i be? if so, can we still have some kind of central humidifier without forced air? also, should i be concerned that our air is not passing through any filters without the forced airflow? both of my boys have asthma and air quality is a very serious concern for us.
thanks

Unknown

If air quality is a concern, then be glad you don't have FHA.

I suggest looking into a proper ventilation system.

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Boilergeek

for air quality look into hrv's from Lifebreath, they also have a true HEPA filtration system

Mike T., Swampeast MO

Humidity

The good thing about humidity is that it tends to be self-equalizing so you don't need humidification in every room.

Homes heated by forced air just seem drier to many? most? people.

Stand-alone vaporization humidifiers are inexpensive and easy to maintain. Perhaps small one(s) in the boy's sleeping room(s) and a larger one in a central location.

I would suggest a decent hygrometer. The digital versions are inexpensive and quite accurate in the typical ranges experienced in a home. You don't want humidity to be too high as this creates its own set of air quality problems.

Very easy to find charts of suggested maximum indoor humidity levels at various outside temperatures on the web.

Centralized systems are certainly available but they can be costly to install, costly to operate (electric generated steam) or a maintenance headache.

don_49

Also

If you're building a tight home,putting humidity in will
not be a issue..Taking it out will be.

larry

Can someone explain how forced air "sucks" moisture out of the air? I accept that moving air around probably increases outdoor air infiltration a bit, and bringing in cold outside air does decrease indoor relative humidity, but my intuition makes me believe this must be a secondary effect in a relatively tight home.

Isn't it true that if you take a closed box of air with a given humidity level at a given temperature, and then heat and then cool the air in that box back to it's original temperature, the humidity level will be unchanged? The relative humidity of the air in the box will decrease as you heat the box, but the quantity of water vapor in the air should remain the same. After the air cools, the quantity of water vapor should still be the same, but the relative humidity should be the same as when you started.

Maybe my simplistic view of what happen in a furnace is way off base. Help me understand this better.

don_42

It sounds

> Can someone explain how forced air "sucks"

> moisture out of the air? I accept that moving

> air around probably increases outdoor air

> infiltration a bit, and bringing in cold outside

> air does decrease indoor relative humidity, but

> my intuition makes me believe this must be a

> secondary effect in a relatively tight

> home.

>

> Isn't it true that if you take a closed

> box of air with a given humidity level at a given

> temperature, and then heat and then cool the air

> in that box back to it's original temperature,

> the humidity level will be unchanged? The

> relative humidity of the air in the box will

> decrease as you heat the box, but the quantity of

> water vapor in the air should remain the same.

> After the air cools, the quantity of water vapor

> should still be the same, but the relative

> humidity should be the same as when you

> started.

>

> Maybe my simplistic view of what

> happen in a furnace is way off base. Help me

> understand this better.

Tom Blackwell

Humidity

You're right, heating air does not "suck the moisture out". The reason FHA systems seem to dry out the air is a matter of air exchange. Forced air systems typically have in excess of 20% duct leakage which causes the house interior to be negative with respect to outdoors, which causes dry outdoor air to be sucked in; hence the notion that heating the air does away with moisture. Humidy does tend to migrate so a locally situated humidifier will do the trick. In cold weather the only humidity loss is infiltration, so the tighter the envelope the less humidity is required. An air filtration unit would help with the iaq, but proper humidity levels would probably do more good.

Brent_2

AC?

Are you having central air installed? What part of the country are you in?

brent

hobojohnny_2

humidity

we are building in western north carolina, tryon area. we will have a central air conditioning system, but we won't likely run it in the winter, which is what concerns me about the iaq since the air wont be passing through the system's hepa filters. thanks for all of your responses.

hobojohnny_2

hrv

thanks again, nrt.rob and tt, the ventilators look like they may be exactly what we need.

jerry scharf_2

how humidity comes and goes in a building

In a perfectly sealed, unoccupied building there would no humidity lost or gained, but that's not much help.

The reason that old houses dry out in the winter is because of the air leakage. When you leak the warm air, you need to bring in the cold air and warm it. As you warm it, it's relative humidity (RH) drops and it feels dry. This is independent on heat source at the same temperature rise. Certainly leaky ducts in a forced air situation only speeds it all up.

So you seal up the house and you're done, right? Nope. Now you have too much humidity. People have this tendency to exhale warm moist air, which cools down and increases the relative humidity. People have also been known to take showers and cook, which also add lots of water to the air. So now correctly operating ventilation exhaust is critical.

The ideal situation is one where you use the ventilation and it's make up air to both keep the fresh air coming in and control the humidity.

If the amount of air you need to exchange to control humidity is less than you need for overall fresh air supply, there are a couple solutions. One is to humidify the air to compensate for the moisture lost. The other is to install an ERV to exchange air and move much of the moisture from the exhaust air to fresh air.

Finally, I just have to correct one thing that people often don't understand. Wintertime air often has very high RH. Don't believe me, then hang your wash out on a winter day to dry. It may freeze but it won't dry.

good luck, jerry

RB_2

Humidity chart based on health concerns...

The conversion down to a small file has left the quality of the graphic less than desirable but you should be able to grasp the messages....

RB_2

design range - temp and humidity

Bob Gagnon plumbing and heating

evaporation

someone explained to me that the moving air in a fha system evaporates the moisture from your body, just lick the back of your hand and blow on it and it evaporates very quickly, it sounded reasonable. Bob

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