High Humidity solution needed

[wxperson]

I have a ranch style home constucted over a crawl space.. where the HVAC unit is located, as well as all of the duct work.

I have a problem where the humidity in the house stays too high.. 60%+. ((other than hot AC days and in the Winter).

I believe most of the moisture is coming up from the crawl space either via the HVAC system and some air "seepage". If I turn the HVAC fan on (without air or heat), the humidity will rise in the house 5-10%.

I am considering 1 of 2 solutions..

1. Dry out the crawl space (3500 sq feet, 3-4' high) with a Thermastor Santa-Fe unit. I assume that lowering the humidity in the crawl will help keep the humidity lower in the house.

OR

2. Use a whole house dehumidifier (Thermastor or Aprilaire) and condition only the living portions of the house..

Which approach would you recommend?

I am guessing that doing both approaches is probably the best option but I don't think I can afford to buy and run 2 dehumidifiers.

Thanks for any advice.

George

PS.. The crawl does have a vapor barrier over the dirt floor.

[airman1]

do both with the thermastor

[parkercie]

Again I agree with airman. The thermastor can work in both areas by ducting it into bothe the crawl and the supply of the HVAC system. If you are going to take this approach, I highly recommend that you pull the return for the Sante-Fe unit from the living area of the house, thus avoiding potential odor problems from the crawl space showing up in your living area. This will also prolong the life of the Sante-Fe's filter(s).

Parker

[wxperson]

Thanks for the replies...

Because the house is on a large footprint (3500 sq feet) I would like to pull the air from the current HVAC return and dump the "dry" conditioned air into the supply plenum of the current system... and also have the current HVAC system's blower run at low speed to circulate the air throughout the house. This is how some contractors suggested installing the Aprilaire 1700 system.

If this approach is OK for conditioning the house.. I am not sure how I can send some of the dry air into the crawl space without making it a "conditioned" space. If I avoid the current central system I have a lot of additional ducting to do to get to the ends of the house and am not sure I would get the distribution I need.

Any thoughts or corrections to my warped way of thinking are appreciated :-)

George

[cool frog]

I HAD A BEACH HOUSE WITH THE SAME PROBLEM. WHAT I FOUND WAS THAT ALL THE MOISTURE WAS COMING FROM THE GROUND. SO WHAT I DID WAS PUT PLASTIC ON THE GROUND IN THE CRAWL SPACE. THAT SOLVED MY PROBLEM WITH THE MOISTURE. IF THAT DIDN'T WORK I WAS GOING TO INSTALL AN EXHAUST FAN TO VENTILATE CRAWL SPACE AND HAVE THAT CONTROLLED BY A HUMIDISTAT.

[uktra]

Before you spend money on a dehumidifyer, you to pressure check your duct system for leakage. If you have a leaky return, this will pull crawl space air into the home. Have you sealed off the vents to the crawl? Have you sealed all the holes from the crawl to the home. Do these things first to lower humidity and save energy. If this does not work- then look into Thermastor.

[Lifer]

First look at the indoor unit to see if it is removing all the condencate.

Then do a load calc on the house to see if it is oversized.
A oversized unit will not allow the unit to run long enough to remove the moisture in the living space.

then you have the numbers to design a system that will take care of yuor needs

[teddy bear]

Originally posted by wxperson
Thanks for the replies...

Because the house is on a large footprint (3500 sq feet) I would like to pull the air from the current HVAC return and dump the "dry" conditioned air into the supply plenum of the current system... and also have the current HVAC system's blower run at low speed to circulate the air throughout the house. This is how some contractors suggested installing the Aprilaire 1700 system.

If this approach is OK for conditioning the house.. I am not sure how I can send some of the dry air into the crawl space without making it a "conditioned" space. If I avoid the current central system I have a lot of additional ducting to do to get to the ends of the house and am not sure I would get the distribution I need.

Any thoughts or corrections to my warped way of thinking are appreciated :-)

George

A couple points to minimize the amount of additional dehumidification needed, cover the earth with plastic, close the air vents to the outside, and tighten the a/c ducts as much as possible. These measures minimimize the amount of moisture entering the home. A 3,500 sq.ft. home/crawlspace requires 135 pints of dehumidification during the cool wet times to maintain 50%RH. The Ultra-Aire 135H is the right sized unit. It's 50% more capacity and removes moisture 50% more efficiently than the Aprilaire 1700. I also suggest not opperating the a/c fan during the a/c season because of rapid re-evaporation of moisture from the a/c coil. Rapid re-evaporation increase the dehumidification load in the home. The U-A should have an independent return from the open part of the home to the U-A. The supply from the U-A is routed to the a/c supply with small adjustable supply to the crawlspace. Continuous operation of the 130 watt U-A blower is recommended. This provides enough air movement to dry the entire duct system during the times of low cooling load. Drying all duct surfaces once a day reduces the potiential for mold growth. Suggest to your a/c contractor that he quote an ULtra-Aire 135H. Its available from his local wholesaler or from the factory.

[-80guru]

I agree with teddy bear, do not run the blower constantly. Check for proper system sizing. Also check to make sure the evaporator is not sized higher in BTU rating than the condensing unit. Also very important , get a thermal expansion valve installed on the evaporator.

[wxperson]

Thanks for all the advice...

I did have a contractor come over today and suggest something a little different..

Duct the dehumidifying unit in "parallel" with a HVAC return line. This would necessitate running the HVAC low speed fan whenever the dehumidifying unit was running (it can be wired that way).

Is there any disadvantage to this approach? Dryer air entering the heating chamber / cooling coils?

This contractor is high on a locally built unit as shown on http://www.healthyairatlanta.com/pr_proffered_humid.asp . It is rated at 20 gallons per day (160 pints). There is a misprint on the page that says 120 pints. I am making sure of the specs before I make any decisions).

Thanks for any thoughts you may have.

George

[wxperson]

One correction.

While a parallel return duct method is shown in the printed doc he gave me, the contractor said they often pull use an existing hvac return as input air into the dehumidifier and then dump the conditioned (dry) air into the main return line of the HVAC system.

Don't know if that makes any difference.

[teddy bear]

Originally posted by wxperson
Thanks for all the advice...

I did have a contractor come over today and suggest something a little different..

Duct the dehumidifying unit in "parallel" with a HVAC return line. This would necessitate running the HVAC low speed fan whenever the dehumidifying unit was running (it can be wired that way).

Is there any disadvantage to this approach? Dryer air entering the heating chamber / cooling coils?

This contractor is high on a locally built unit as shown on http://www.healthyairatlanta.com/pr_proffered_humid.asp . It is rated at 20 gallons per day (160 pints). There is a misprint on the page that says 120 pints. I am making sure of the specs before I make any decisions).

Thanks for any thoughts you may have.

George



The unit is a knock-off of the Ultra-Aire 150 from a small company. Unit looks OK and is more efficient than the Aprilaire. It's important to be able to operate the dehumidifier independent of the a/c fan to avoid re-evaporation and high operating cost. Also the 160 pints is more capacity than you need. What's the value of a proven design from a manufacturer building many thousands of UL listed dehumidifiers with a five warranty? Many of the large a/c contractors in the Atlanta area have been installing the Ultra-Aire for several years.

[wxperson]

Thanks for your comments.

The reason this unit interested me is because of th 160 pints/day. That is because I want to duct some of the "dry" air into the crawl space.. I figured 160 was better than 130 pints/day.

Thanks,

George

[uktra]

You won't need to duct air into the crawl. Home air goes into the craw anyway. The most important thing is to keep high humidity air from the outside going into the crawl--as well as vapor from the earth. Also your ducts in the crawl are very important. If your return leaks more than your supplys, a negative pressure is in the crawl pulling air from outside into the crawl and into the home. This also wastes energy. These things should be checked first before spending on a dehumidifyer that uses energy.