Renovated Hydronic System and Dry Air

[kayjh]

I have a puzzling problem. I live in a 1950's - 3,200 sq. ft. ranch style home in central Canada. The house is heated with cast iron baseboard heat. In September, I replaced an old boiler with a new Weil MacLain Ultra and installed a Tekmar control system. The Tekmar system manages 6 zones (up from 4 previously) and includes an outdoor temperature sensor. It also has the ability to control our recently installed air condtioning system.

Last year we installed a forced air central air conditioning system with all duct work in the attic space. There are two separate duct systems (one for the living room dining room and den, the other for the bedroom wing). ECM motors are used in the air movers. Heaters were installed in the main ducts to guard against condensation build up in the ducts during the winter months. THe ECM motors are set to run slowly, circulating some warm air to keep the ducts dry. We don't use this system to heat the house.

Installation of the new heating system began in October and we have had several control issues with the Tekmar system. About 3 weeks ago, the HVAC company that did the installation replaced all of the thermostats and the main Tekmar control in the boiler room - the result is the system now maintains the set point for heat in each room. At the same time the technician slowed down the air movement in the ductwork. Finally, he adjusted the target hot water temp (boiler) downward to even out the hot/cold swings in the baseboards - i.e. we have a lower target temperature, but the pumps run longer in each cycle, to satisfy the heating requirements in the house. There is warm water in the rads at all times.

My problem: Since the last adjustments in the house 3 weeks ago, the air has been very dry. The technician tested the indoor air today and found the humidity to be just 22%. Outdoor temperature is currently +25F. At night the temps drop to about +5F.

I am at a loss to understand why we are having a low humidity condition now. Up until 3 weeks ago, the thermostats were behaving erratically (which is why they were replaced), but the humidity was comfortable - even when the outdoor air temperatures were as low as -30F.

I have had the technician come back to the house and reset the target boiler temp to what it was 3 weeks ago to see if that helps. The next step will be to shut off the air movers to see if the electric duct heaters are drying the air out. It didn't seem to be a problem last winter though.

We can always install an HRV system and humidifier, but I'd like to try and solve the problem without having to throw bags of money at it.

Any ideas as to what could have gone wrong?

Thanks,


kayjh (desperately dry and waiting)

[tinknocker service tech]

the induct heaters are drying out your air durning thier run time. You can have them ajusted to run less and still allow them to keep the ductwork dry

you can also have a remote humidifier agged to them to maintain proper humidity level. I say remote because i dont like humidifiers in attics but this is done all the time if freezing is a major concern

just so you know also if on hi himid days and the ac just cant get the humidity down in the house you can use the inline heaters if set up correctly to remove the humidty and have the stat at a comfortable temp

[BaldLoonie]

How can heaters dry the air? They don't have a condensate pan under them. True the RH is lower in the hot air but the heaters aren't the culprit.

A house is dry from infiltration. Outside air leaks in however, gets heated by ANY heating source and while no moisture is removed, because warm air can hold more moisture, the relative humidity is lower. The more air leaks in, the drier the house is. My house is very tight so even at 5° above, I have no humidity issue. People in foamed houses that are extremely tight often have to ventilate or run a Teddy Bear sized dehumifier.

If this started with the forced air system, I'd first suspect leaks in the return duct sucking in cold air from the attic. This increases total infiltration and both the strip heaters and the boiler heat is warming it causing the low RH%.

[kayjh]

the induct heaters are drying out your air durning thier run time. You can have them ajusted to run less and still allow them to keep the ductwork dry

you can also have a remote humidifier agged to them to maintain proper humidity level. I say remote because i dont like humidifiers in attics but this is done all the time if freezing is a major concern

just so you know also if on hi himid days and the ac just cant get the humidity down in the house you can use the inline heaters if set up correctly to remove the humidty and have the stat at a comfortable temp

Thanks for your reply.

I'm not sure the in duct heaters are the problem as the humidity was still low after I shut them off for several days. I wonder if the slower air moving through the heaters will "super dry" the air - i.e. dry the air more than if the air was moving over the heater elements more quickly??

Can you explain what a remote humidifier is? Please keep in mind that outside air temperatures can be -35F here during December - February. Isn't adding humidity to the air movers/attic duct work defeating the purpose of having heaters in the ductwork and constant air movement - ie.e to keep condensation from forming in the duct work?

kayjh

[kayjh]

How can heaters dry the air? They don't have a condensate pan under them. True the RH is lower in the hot air but the heaters aren't the culprit.

A house is dry from infiltration. Outside air leaks in however, gets heated by ANY heating source and while no moisture is removed, because warm air can hold more moisture, the relative humidity is lower. The more air leaks in, the drier the house is. My house is very tight so even at 5° above, I have no humidity issue. People in foamed houses that are extremely tight often have to ventilate or run a Teddy Bear sized dehumifier.

If this started with the forced air system, I'd first suspect leaks in the return duct sucking in cold air from the attic. This increases total infiltration and both the strip heaters and the boiler heat is warming it causing the low RH%.
electric

I understand what you are saying, but why is it that a room heated with baseboard always seems to dry a room out more than a forced air system?

As for air infiltration, I'll have the techs double check the intakes. There are only 2 intakes (24" x 24") and I'm pretty sure they are well sealed. When the a/c system was installedin the summer of 2006, all of the ductwork was mastic sealed, taped and two layers of fiberglass (aluminum backed) taped to the outside of the pipes.

I should point out that the dryness only started about 3 weeks ago after some adjustments were made to the boiler system and air movers.

Thanks,

kayjh

[BaldLoonie]

Actually the hot water gurus would say your hydronic heated house would dry out less than one with scorched air, as they call it. And that is just because of how leaking duct systems can be bringing in air from outside of the conditioned space.

You might find an energy consultant in your area that can do a blower door test to see where the leaks are so you can fix.

[kayjh]

Actually the hot water gurus would say your hydronic heated house would dry out less than one with scorched air, as they call it. And that is just because of how leaking duct systems can be bringing in air from outside of the conditioned space.

You might find an energy consultant in your area that can do a blower door test to see where the leaks are so you can fix.

Thanks BL,

I'll have the installer look into it. I think it's a long shot though. Prior to the a/c ducting being put in, we evacuated vermiculite from the attic. We then hired a company to air seal the attic from the house with foam (all ceiling fixture boxes, wall top plates, etc.), installed air chutes at the attic edge above the soffit, installed ridge vent on the new roof and blew in R50 of cellulose insulation. As I wrote earlier, all of the attic duct work has been triple sealed with mastic, tape and 2 layers of insulation wrap.

The only place I can think air could leaking in is around the edges of the 2' x 2' intake grills, but you would think opening the air handler would expose a bunch of insulation sitting near the fan - which would have to be sucked in with the air that was leaking. We didn't see any evidence of that. After closing the cover on the air handler, the service tech taped the edges to ensure a complete seal. Perhaps I can scheck the condensate drain assembly to make sure nothing is leaking there.

The frustrating thing is that this problem just started.

Thanks for your replies.

kayjh

[firecontrol]

First of all it's usually a mistake to jump on the last thing that was changed or done to blame for all things changing in the home. When a problem arrises it takes no longer to look at everything one thing at a time starting with the preceived problem and working backwards.

Humidity stabalization in a home is a variable that doesn't easily get fixed with fancy gadgets and the "perfect" control. What these do is usually mask what might be a bigger problem that should be addressed first.

Fact: If humidity/moisture/water vapor is produced in the home it will stay there forever until it finds a way to move/escape to a less humid air mass. Usually this less humid air is outside. So... some way the humidity that was always normally in your home till a few weeks ago has somehow found a new way to escape out of your home. I'm not saying that it has nothing to do with the setpoint being changed. What I'm suggesting is that something that changed at the same time or around the same time the setpoint changed is what is more than likely causing the indoor humidity to escape. OR something that the occupants of the home changed in their daily routine at the same time or because of the new conditions that were experienced when the setpoint was changed. You're the only one that can think about this and answer that question.

Start by thinking about everything that produces humidity in the home. Your breathing, cooking, taking showers, watering indoor plants, taking baths, leaving doors open between rooms or other parts of the home, using different rooms more frequently that you weren't before, someone is getting to warm at night and is opening a window, a new pet came into the home that has to be let outside every hour......... get the idea?

Each thing above produces or reduces the humidity in your home.

A steady and constant heat output from the radiators will generate constant air currents in the home. These air currents can contribute to air infiltration in a home in certain circumstances and conditions.

Did the weather change abruptly in the last 3 weeks? The wind outdoor blowing from a different direction on a steady basis? Have you checked the attic out to see if some new "visitors" with four legs and sharp teeth have moved in and have ventilated your tightly sealed up air conditioning system? Do you get heavy frost in the ground where you live that has a tendancy to lift things out of position? This can sometimes open up cracks in foundations or the building structure.

You mentioned you had installed an Ultra boiler. I will assume this means a chimney exists that was used for the old boiler? A cap or plug falling out of a chimney can move a tremendous amount of air OUT of the home so can a large crack in the same chimney.

Hope I didn't make things worse by giving you all this information, but if all that's done is to add a humidifier to bring the humidity back up, the reason it went down won't be addressed and sometimes these problems can cause major structural damage.

Good Luck.

[johnsp]

Turn the fans off for a week. See if it changes anything. Can the duct heaters be run without the fans on?

[kayjh]

First of all it's usually a mistake to jump on the last thing that was changed or done to blame for all things changing in the home. When a problem arrises it takes no longer to look at everything one thing at a time starting with the preceived problem and working backwards.

Humidity stabalization in a home is a variable that doesn't easily get fixed with fancy gadgets and the "perfect" control. What these do is usually mask what might be a bigger problem that should be addressed first.

Fact: If humidity/moisture/water vapor is produced in the home it will stay there forever until it finds a way to move/escape to a less humid air mass. Usually this less humid air is outside. So... some way the humidity that was always normally in your home till a few weeks ago has somehow found a new way to escape out of your home. I'm not saying that it has nothing to do with the setpoint being changed. What I'm suggesting is that something that changed at the same time or around the same time the setpoint changed is what is more than likely causing the indoor humidity to escape. OR something that the occupants of the home changed in their daily routine at the same time or because of the new conditions that were experienced when the setpoint was changed. You're the only one that can think about this and answer that question.

Start by thinking about everything that produces humidity in the home. Your breathing, cooking, taking showers, watering indoor plants, taking baths, leaving doors open between rooms or other parts of the home, using different rooms more frequently that you weren't before, someone is getting to warm at night and is opening a window, a new pet came into the home that has to be let outside every hour......... get the idea?

Each thing above produces or reduces the humidity in your home.

A steady and constant heat output from the radiators will generate constant air currents in the home. These air currents can contribute to air infiltration in a home in certain circumstances and conditions.

Did the weather change abruptly in the last 3 weeks? The wind outdoor blowing from a different direction on a steady basis? Have you checked the attic out to see if some new "visitors" with four legs and sharp teeth have moved in and have ventilated your tightly sealed up air conditioning system? Do you get heavy frost in the ground where you live that has a tendancy to lift things out of position? This can sometimes open up cracks in foundations or the building structure.

You mentioned you had installed an Ultra boiler. I will assume this means a chimney exists that was used for the old boiler? A cap or plug falling out of a chimney can move a tremendous amount of air OUT of the home so can a large crack in the same chimney.

Hope I didn't make things worse by giving you all this information, but if all that's done is to add a humidifier to bring the humidity back up, the reason it went down won't be addressed and sometimes these problems can cause major structural damage.

Good Luck.

Thanks for the suggestions firecontrol,

I agree that it is a mistake to jump on the last change that was made, as it may be something that happened coincidentally at the same time that resulted in the change. I had tried, last week, to isolate all of the variables that may have changed, resulting in a change in the indoor environment.

The weather would be an obvious one to consider, however the weather seems to have been getting warmer over the last month, as we approach spring. This would require less heating, so a humidity drop should be less evident.

I appreciate that humidity created in the home will stay in the home until it has a way to escape, however I couldn't identify any change in the building envelope over the past month.

The Weil McLain Ultra does use the old brick chimney to draw fresh air for combustion and exhaust the spent gas, however the pipe opening at the base of the chimney was re bricked and sealed after the new pipes were installed.

We have a central exhause fan for the 3 main floor bathrooms mounted in the attic. These are controlled by individual (up to) 30 minute timers which results in a 200cfm outflow of air while running. The contractor was concerned that there was a fault with the system, resulting in a 200 cfm draw 24/7. this would account for an 18,000 btu loss of heat per day (replaced by cold dry outside air). After checking the system, we discovered that the exhaust fan was not at fault.

I hadn't considered animals in the attic, but cold air infiltration would have to come from the intake side, right? In this scenario, cold dry air from the attic space would be sucked into the air negative pressure side and injected into the house. I'll have to look into this, but I think it is unlikely. All of the ductwork is solid, with the exception of about 2' of flexible insulated on the supplies to some of the ceiling vents. The main ductwork is 16" round solid, with the branch lines being 6" round solid. All of it looks to be in good condition.

After considering all of the good advice on this forum (including your post), I had the heating company reset the boiler heating profile back to what it was a month ago. With similar outside weather, we've gained 13% RH in one day and the house has been holding this humidity level through the weekend. The house is much more comfortable with a steady RH of about 38% (outside is about 30F).

For the next several days overnight lows will be about 1F. It will be interesting to see how the RH holds up. If it drops, it is back to the drawing board. If it holds, I'll have to continue the search for an answer to the problem.

It seems that in my case, having the radiators carry less heat, but for a longer period of time has the effect of lowering RH in the house. It is hard to understand why this is. Perhaps an environmental engineer can weigh in here.

I will say that although it has taken some time to get it working right, the Tekmar control system is pretty versatile at controlling how the Weil Mclain boiler delivers heat to the house. In a perfect world, I would have left the system running longer heat cycles with lower temperatures vs higher boiler temp and shorter run times. It seemed to make for more even heat; however having said that, the system is capable of controlling my hydronic heat system within .5C of the set point in each of the 5 zones we have in our house. I'm sure I can return it to this mode of function once I determine why the air is drying out in this mode and what I can do to avoid it.

We are planning on the installation of an HRV this coming fall with will be able to help control humidity as well.

kayjh

[kayjh]

Turn the fans off for a week. See if it changes anything. Can the duct heaters be run without the fans on?


Hi John, thanks for the suggestion.

The air movers were shut off last week with no improvement in RH. We can't run the duct heaters without air flow as there is a built in protection mode to avoid overheating. Turning the airmovers (and heaters) off didn't improve the situation. As I posted above, it seems that shorter heat cycles at a higher boiler temp has improved things. This is the way the system was originally set up in November without us noticing any drop in RH. We'll have to wait and see how things work out over the next several days of cold weather (will spring ever get here??).

kayjh :)