Hello to all. After much research I have come to the conclusion that I must install an energy recovery ventilator (air exchanger) in my 5 year old, 2,000 sq. ft. ranch home. Hopefully this will cure my woes of condesation on my windows in cold weather. My heating contractor says I should install a humidistat on the unit to control the humidty. My dilema is that I talked to a factory rep that indicated I was better off installing a timer on it so that the air would exchange a certain percentage every hour. Anyone know which way I should go- humidistat vs. timer? Thanks, Ken Molitor
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I've always thought the humidistat was the smarter way to go. Why not run your furnace on a timer by the same token?
The factory rep may be more of an authority. Try a second opinon at a second source of HRV and ask why they recommend that and see if it makes sense to you.
Please share the info.
Stu
Either works. Either would have to be adjusted periodically. The humidistat less so.
A timer would be preferred in my mind if you needed some set % (i.e. 1-2 air changes per hour). That would be the case, perhaps, for a super tight house (like mine). Then you could diddle the timer up and down to try to control condensation as it varies with moisture generation and with outside temps.
A humidistat, however, would be better if you are trying to control humidity (which you are). Dial in a setting that keeps the windows from having condensation (maybe 40% in mild outside weather) and let it run as needed to maintain that. It will run more in the morning when everyone is taking showers, when you've got the pasta pot boiling and during all the heavy breathing during orgies. When no one is home, it will run a lot less and save some energy. You still have to twiddle it for outside temp, but that is an empirically observable relationship (lower outside temps requires lower indoor RH to avoid condensation) and you don't have to adjust for varying moisture generation.
I'd strongly go for the humidistat. If you can, place it nearest the problem windows or between said windows and the moisture sources. Then you'll be controlling the problem when and how is occurs.
Note that when it is really cold, you won't want to totally eliminate condensation. Sure, you might be able to air exchange down to 15-20% indoor RH, but your lips will bleed, your hands will crack, everything will have incredible static charges, and the cat will shred your face and crap in your shoes after you inadverently zap her nose with 2,000 volts (albeit a very low amperage).
But whatever minimum humidity is acceptable to you and your cat, the humidistat would be the easy way to control that.
The main winter problem with the humidistat would be that under certain circumstances the unit wouldn't run often enough to maintain air quality. However, the same activities that generate humidity (people breathing, taking showers, cooking) tend to be the ones that lower air quality, so it would work out OK, mostly.The main activty that affects air quality without raising humidity is outgassing of building materials, but that's not likely to be a major problem in a 5 YO house.Keep in mind, though, that in summer a humidistat won't work at all (or, rather, will work all the time), if the outside humidity gets up above your setpoint.Re adjusting humidity based on outdoor temperature, you might consider buying a humidistat with outdoor temp sensor, such as those sold with Aprilaire humidifiers. You'd likely need a relay to reverse the "sense" of the unit, but that's simple enough.
If ignorance is bliss why aren't more people
happy?
Would it be possible to use both timer and humidistat, so that the unit ran a certain length of time each day to maintain air quality, but longer if necessary to remove humidity?
Yes, I was going to suggest that. The simples would be a cycle timer that you could set to run X minutes out of an hour. The simples would be to parallel them.A somewhat better system would be to use a SPDT humistat and wire the cycle timer timer on close on low side. Thus the timer only runs when the humidstat is not running the HRV.
absolutely, and it's what you should do.You are doing more than controlling humidity here. You are providing for indoor air quality. If humidity is all you need to control, use a dehumidfier and save yourself a ton on ductwork. But it sounds like you probably have more than just humidity problems... it's pretty rare for *just* humidity to be a problem in a tight house. Headaches, stuffy noses, frequent colds... all indicators of poor indoor air quality.Size the unit properly, make sure you can boost it during periods of high need, and hook up a humidistat as well. And breathe easy.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
After years of condensation on windows, I bought a dehumidifer yesterday at HD (made in china) ((double apologies there)) and within 1 day the low e thermopane vinyls have cleared up. The house is 1100 sq ft. 2 occupants and a dog that gets let out about 10 times a day. I think the main problem with the baseline humidity (45-50 %) is the number of houseplants.Temperature in the house is a balmy 64 at the moment and humidity is around 40 %. In the 24 hours I have had the dehumidifer I have dumped about 2.5 gallons of water down the drain. Seems to be working quite well.
Keith
NRTRob, saw your post and want to clarify with you. You would do the timer and humidistat? I am going to be spending $1650 on an ERV unit so I want to make sure that it is installed in the best way, be it either a humidistat or a timer, or both. My family consists of my wife and me, 2 boys, 2 cats, and a dog living in a 2,000 sq. ft ranch home. We have gas forced air for heat. It gets pretty drippy in the house when the temp. drops and my windows are taking a beating. I appreciate your advice. Thanks! Ken Molitor [email protected]
Be careful with the timer!! Some surprises come with them unless you have the right unit.
You almost need two timers with the humidistat setup: One to ensure minimum run time and one to limit maximum run time.The big box stores don't generally carry the type of timer you'd want -- will probably have to order through an HVAC supply house (though I suppose a timer generally comes with the heat exchanger).
If ignorance is bliss why aren't more people
happy?
Most HRV/ERVs have controllers you can buy for them to set the unit's operating characteristics (high speed, low speed, intermittant, etc). If you are exhausting bathrooms with it, there are also twenty minute boost timers out there you can use to trigger boost from the bathroom, just like an exhaust fan, but timed.I would then add a dehumidistat to that to allow the unit to boost itself if your humidity requires it.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
You can't/shouldn't be counting on the HRV to replace a bath fan. From 1981 -1984, we put only ERV/HRV's in on the advice of the manufacturer- "this is all you need for ventilation now". By the end of 1984, we were putting bath fans back in- some vented to the HRV system and some vented to the exterior but both on line voltage hand crank timers. We started to custom design each house, depending on what windows ( how much resistance to condensation?) , jet tubs, hot tubs,etc were going in.
When a bathroom timer turns the whole unit to high speed, all the boosted air volume does not come from that location. You also will have boosted exhaust venting (plus supply venting) in up to 3-5 other rooms but no one may being using these rooms and they don't need the extra venting!! I have seen a fairly upscale home that had to put a bath fan in after the master bath would not dry out by noon using the HRV only.
ERV/HRV's are general air quality machines only. They are not designed to be spot or dedicated ventilation.
The ERV/HRV industry is not fully mature yet....it's getting close but just not there yet. Every time I see the NE/Maritimes sales rep for the largest manufacturer, I'm asking for the integrated or add-on programmable timer for his units- IMO, the best on the market now; tho' in the 80's-early 90's would not touch the product!
Well, I always tell my clients what to expect depending on the dedicated CFM I have available per bathroom. That is, things like "this won't clear steam as fast as a bathroom fan", for instance. In most cases, you should be able to get the CFM you need on a continuous basis to keep a bathroom from having moisture problems. Obviously each job is different, but generally I find it's doable.I disagree with your assessment on other basis as well. So what if the extra rooms don't "need" the extra venting? If you trigger a 100CFM bath fan, that air is coming in from somewhere, untempered, and the air you blow out is blown out hot. I'd rather exchange the heat out of the outgoing air (and possibly humidity) and replace it with tempered air. And generally speaking, you're only increasing your overall exchange rate by about the same amount as that 100cfm bath fan. It may not clear all the steam right then, but when it settles back down to low-level exhaust, it can finish the job.Finally, if your house is tight enough to require IAQ ventilation, you probably exceed your allowable negative pressure with bathroom fans.It's not good enough for some, to be sure. But generally the clients I work with are willing to deal with it for the efficiency gain.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Rob:
What do you do with a 70 ft long house with HRV at one end and the master bath at the extreme other end. Do you think the 4" branch ducting will give it a lot of OOOMMPH? Especially when there are 3 other baths/ half baths, kitchen, laundry and basement gym on the same exhaust trunk. This long run could have over 350-400 equivalent feet of duct on it!! Exhausting or boost bath fan.
Of course, there are situations that aren't easy to solve... no doubt about that. I'm not saying HRVs are a panacea for all jobs.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
In most cases, you should be able to get the CFM you need on a continuous basis to keep a bathroom from having moisture problems.
That's our situation. We do .5 ACH and never run the bath exhaust during the winter. Summers, every shower, but that's due to our high dehumidification requirement.
Good design obviously helps. For us, that includes pressurizing the house with unequal exchanger fans.PAHS Designer/Builder- Bury it!
Oh! The old original standard appears before my eyes- 0.5 ACH. This was the standard that the early (1983-87) Canadian R2000 superinsulated home program started at. (by the way, Joe Lstiburek of BSC worked in this program)
I was a site advisor/inspector/trouble shooter/researcher for this program in New Brunswick until 1992-3, (Two of my builder/clients were named Canada's "R2000 Builder of the Year" in 1989 and 1993) so I became quite intimate with all the problems that the original prototype ERV/HRV's coming out of inventor's back yard shops and basements had. As well the overdrying, improper balancing, cold air delivery, ice/frost/condensation on/in the insulated duct sleeves (39 out 40 houses inspected in 1986), various defrost problems from damper motors to stuck dampers to broken belts to over designed belts- all were in my learning curve. I was hired by manufacturers to travel to 3 provinces troubleshoot units that local dealers could not get operating satisfactorily....and it goes on. My first installation was a desiccant heat wheel ERV in 1981 which now seems to be coming back again after all the competitors ran it down and many installers could not get them working properly.
Now back to the 0.5 ACH. Since that original value, the program has reduced the volume requirements 3 times and, most likely, there is a final downward adjustment coming. Presently, in the R2000 program, the rate is based on a room count method with 25% reduction if you put together a "healthy home" through better choices of installed materials with regard to offgassing. The final downward adjustment of ventilation rates may be based on occupant #'s since, after all, when offgassing is diminished, it's their actions that produce the biggest need for clearing the air.
Tom, Va is not the vast cold northern half of your country. At that original rate (high: erring greatly on the side of safety) we were getting complaints of nosebleeds, itchy eyes, cracked lips, shocks, shrinking HW floors, high energy bills, etc. from January through to March in our 8,000 -10,500 degree day F climate.
Mix and match the old (fans) and the new (HRV/ERV) is the longterm way to go. Buy up in models, since most contractors sell the "contractor's (read: stripped down, cheap unit with minimum controls) model" or "special" for pricing reasons. When I tell new homeowners (like yesterday at a new house closing inspection) what they could've got for $500-$1000 more they are not entertained. The house was $375,000 but had the lowest priced unit from this manufacturer. If you wanted to change any unit functions except the dehumidistat, you have to walk down to the basement. It's like having the cheapest Walmart tires on your new Mercedes!!
So you would advise people to get exhaust fans as well as ERV ducting in the bathrooms? I'm asking because the ductwork is going in this week for our ERV, and we just noticed the electrician was putting fan boxes in the bathrooms. Should we tell him to take them down, or leave them up? Would you just exhaust those to the outside?Am I correct in thinking you can't exhaust or pull air from under a porch for ERV's (screened with lattice or something similar)? That's what the HVAC people are planning on doing (one or the other), and it seems very wrong to me.We have SIP walls, conventional wood trusses with R-50 cellulose going in.Thanks!
Jo
IMO, you want at least 50 CFM in a bath where showers are taken, and preferably 75-100 CFM. Will the ERV achieve that?
If ignorance is bliss why aren't more people
happy?
No, not with a distributed system in a larger home with longer duct runs and 4-8 exhaust points- kitchen, 4 baths/ half baths/laundry/home gym. You really want at least 100 cfm intermittant from the kitchen and then what from the others- a total of 200 more intermittant. That's a big ERV/HRV and ducting.
You only need that rate if the exhaust is intermittant. that said, you can often achieve 50cfm or close to it with HRVs/ERVs with a boost capability. THAT said, you don't really *have* to unless you're picky about steam. continuous exhaust will clear the moisture over a longer period of time, still making sure your IAQ is good over the long term.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
In a common small bath, if you take a shower, you need 50 CFM to prevent major condensation on the walls, 75 CFM to keep major condensation off the mirrors. A lower vent rate won't hack it.
If ignorance is bliss why aren't more people
happy?
You're missing the point... what is the goal? eliminating condensation, or providing for good air quality? If the clients are picky about condensation, so be it... do what you have to do. If they are concerned with air quality though, then provide for air quality.Periodic condensation isn't a problem, as long as it dries out, and it will with continuous ventilation. Just not as quickly.That said, you can get more CFMs by boosting the exhaust fan on high speed. You may or may not have 50 CFM, but you'll have something over the 20cfm continuous required by ASHRAE.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Not being "picky" about condensation. If moisture collects in drops on the walls it causes damage.
If ignorance is bliss why aren't more people
happy?
it's not going to be raining from their ceiling with a lower level exhaust ;) if it gets a little moist though, it's not the end of the world as long as it doesn't stay that way and allow mold growth. The only complaint I've ever had is foggy mirrors. Thus my discussion of expectations prior to the installation with the client.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
If nothing else, water running down the walls causes staining.
If ignorance is bliss why aren't more people
happy?
understood, and I reiterate, you shouldn't see that kind of condensation with a lower level of exhaust. We're really not talking a small drop here. Maybe if you have a spa shower in the room or something, I could understand being more conservative, but with a standard shower setup and watching your CFMs, an ERV can handle the exhaust requirements of most bathrooms.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
It probably depends a lot on the temperature of the walls, and their ability to "sink" heat. Cold plaster walls can condense a lot of moisture in short order.
If ignorance is bliss why aren't more people
happy?
That sounds like a keen observation to me, actually. I would think if the house is tight enough to need an HRV, that wouldn't be a real big problem, but then.. who knows what people are setting their temps back to as fuel prices rise.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
No joke, one of the best threads in months if not ever.
There is not much I do not arrogantly claim to know, but this thread has had some really good technical content. Would one of the contributors to this discussion forward this to J Fink (see editor threads), I myself would like to see a good FHB article made out of the contents of this thread.
NO, do NOT look this way for somebody gullible enough to try to pull anything together.
I have a different problem here. I live in the high desert; that means RH in the 10-30% range after heating. If I use a HRV, am I going to need a humidifier to get the house up to about 40% RH?
Erich
There are units that preserve (some of) the humidity, I believe, by using a rotating dessicant medium.
If ignorance is bliss why aren't more people
happy?
These are called "heat wheels". There are two, maybe three, residental brands available.
Venmar "Duo" http://www.venmar.ca
Stirling "Recoup-aerator" http://www.ultimateair.com/
http://www.airxchange.com/ May be commercial only now; I installed their units in 1981.
Edited 12/17/2005 9:03 am ET by experienced
Definitely.......or really tighten up the house and use a high moisture transfer ERV (probably still need a small humidifier but it will run less).............or get lots of tropical plants (need lots of water; not like cactuses), terrariums, aquariums, pets
Edited 12/19/2005 7:49 pm ET by experienced
Have a fountain in the house...or a water sculpture.
Rob:
The brand of ERV/HRV you sell has three different remote control/dehumidistat wall units with 2 of 3 having the "20 min air exchange" with "40 min at rest or air recirculation/filtration" modes. Now why do you think they offer this in 2 of 3 models? They are the largest manufacturer and they know most people are being overventilated so offer the better controls (only about $100 more). If the dealers don't explain the differences/options, will they know?
Most people in overventilated situations don't know the difference. If the air is nice and fresh in a house with the "right" adjusted amount of air exchange and recirculation for that family, if you add 50 or 100% more air, will they notice the difference when they come home from work? Will the air be any fresher? If you now add another 50%, is it any fresher? So how do people know? The air is always fresh when they walk in, so it must be alright!! But they're paying more than they should.
Totally agreed.. thus, you run the fans at lower speed or intermittant (or, timed) for common usage, while retaining the boost exhaust speed you need. In *most* cases I come across anyway. For really large intermittant exhaust needs that may not be achievable, of course.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Yes , I'd keep the fans but find out the cost. You don't need the highest priced units as these are a supplement to the main system. If you wish there are some very quiet, energy efficient fans from Panasonic (Whisper series). Vent them to the exterior and have them controlled by hand crank or electronic timers.
Be careful of the placement of the Intake hood. Under the porch, veranda, deck is not acceptable. Be careful of other sources of future odour/pollution like the driveway, garbage storage, dryer exhaust, gas/oil sidewall exhaust, neighbours exhausts if fairly close and low (eg. pellet stove within 20-30 feet).
Sounds like you've got a good start on an efficient home. Make it as tight as possible now- you only get one stab at it! Don't get a contractor's "model" or "special" for an ERV/HRV- these are stripped down versions of the originals with not many control options and little in the way of remote controls. Good luck!!
experienced - VaTom's house is buried in the ground, and his HRV is homemade...
So the parameters are skewed, but his air is clean.
Is an eighth of an ACH really enough for my new ICF home?
Treat every person you meet like you will know them the rest of your life - you just might!
For the first 6-12 months while materials are new and offgassing their chemical odour, I would be at 1/3 ACH or higher if necessary. Its hard to know about after that as I don't know your lifestyle, # of plants, # of occupants and for how long each day, etc, etc. For a couple in a large house, 1/8 ACH should be enough, especially if you have additional bath fans.
Edited 12/15/2005 11:04 pm ET by experienced
The old original standard appears before my eyes- 0.5 ACH. This was the standard that the early (1983-87) Canadian R2000 superinsulated home program started at.
Yup. That's the vintage of our house, 4166 degree days. None of your problems at all, or I would have altered it. Another factor you apparently don't deal with is radon. This is a moderate risk area. Not an issue for this underground dweller. Like Cloud, we use a filter on our dehumidifier to remove objectional debris from the air stream. We also have the best air of any house I've been in. And the house never gets cold, ever.
You lost me on your last paragraph. I built our exchanger using aluminum for the core. Similar to Lossnay, the plan that I altered came from Popular Science. Works admirably.
Ventilation systems are all but unheard of here. HVAC guys are really HAC. Our local code enforcers consider operable windows adequate. Not that open windows would be considered normal for well over half the year.
Oh, $375k would hardly be considered Mercedes class here. My neighbor's asking $1.3m for her 3500 sq ft. That's without any ventilation system.PAHS Designer/Builder- Bury it!
Well, perhaps I'm crazy...In our home, we hooked up our HRVs to suck air out of the bathrooms. They do this at the lowest speed, constantly. An occupancy sensor in each bathroom turns on the HRV into high-speed mode every time someone (or something) enters the bathroom. A timer in said occupancy sensor mthen turns the HRV back into low-speed mode 20 minutes later.Assuming that each bathroom has the same length of ducting between it and the HRV (and ours largely do), we get the 100 CFM during high-speed in every bathroom and 8+ air changes per day. Despite very low temperatures around here, the bathroom windows only fog slightly as the shower runs or someone wet exists the shower. 5 minutes later and they're clear again.There are very good instances as you point out when localized exhaust fans make much better sense than tryong to shoe-horn a HRV/ERV to fit all purposes. Yet, I believe that with the right kind of home design that an HRV/ERV can be an effective bathroom fan.
After 28 years of working with airtight homes and ERV/HRV's', part of it in a monitored and researched program, one thing I've found is that the vast majority of houses are overventilated. This is backed up by the actions of the largest manufacturers- they started using (1) extra low speed running modes in the 1980's, (2) re-circulation modes and (3)programmable timers/timed air exchange periods/off periods in their control strategies.
Most of us are buying/building cleaner homes and living cleaner lifestyles in them (no smoking, less chemicals in materials/paints), so the need for ventilation is decreasing. This was said years ago by American Architect and Indoor Air Quality specialist Hal Levin- it's easier and cheaper to leave the chemicals and other indoor pollution out of large buildings than it is to build ventilation systems 2 and 3 times larger (at capital costs of hundreds of thousands to millions more and yearly operating costs for heating/cooling/humidifying/dehumidifying 2-3 times more air.)
We are building airtight homes for energy efficiency and also, in some cases, health reasons (See http://www.healthhouse.org -builder guidelines; Both Joe Lstiburek {co-chair} and Hal Levin on technical committtee). Is it necessary for 24 hour ventilation, when during the day, most working class homes are not occupied (so who's creating all the pollution that needs to be ventilated?). At night, people are asleep so we don't need the ventilation active bodies would. Yet we overventilate and some people go to putting humidifiers on their furnaces to overcome the low RH's.
The overventilation costs us $$$$$ from the earlier replacement of fans/units through more use than necessary, higher air reheat costs due to higher than necessary air volumes (and some units are as low as 50% efficient), higher defrost costs (some units have electric defrost heaters), higher electric running bills (luckily not much though). The more you overuse the units, the more you take monies out of your pockets to give to a utility/fuel company, just the reason you built the highly efficient, air tight house in the first place- not to give that money to them!!!
Edited 12/16/2005 7:33 am ET by experienced
Edited 12/16/2005 10:15 am ET by experienced
Re the cat, one winter when I was a teen I was in a devilish mood and several times took our cat (who loved to climb in the Christmas tree) and carried him (shuffling my feet) across the LR floor toward the tree, holding him nose-first until a piece of tinsel jumped out and zapped his nose. He got to where he didn't even want to go into the room.The next year, without thinking, I carried him into the LR, where the Christmas tree had just been set up. He took one look, lept out of my arms, and dashed out of the room.
If ignorance is bliss why aren't more people
happy?
Just lost a post that took over 1/2 hr to compose on hrv/erv's!!!! Been installing/specing them since 1981. If you want to talk about them, private e-mail me and we can probably do a phone call.
I hate this program---lose posts every second day.
Write in Word, cut and paste.Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
Check out http://www.buildingscience.com depending on where you live, you can save yourself a whole lot of money by just using an Aprilaire 8126, it is a motorized damper and fan cycler that connects with one duct to your existing FHA return to bring in dry, fresh outdoor air