any problems with bypass humidifier and variable speed furnace blower

[Chris Friesen]

I'm in the Canadian prairies...cold and dry in winter. I'm looking at getting a whole house humidifier (using a big console one currently, getting tired of cleaning the basin). I've got a two-stage gas furnace with a variable speed blower. (Armstrong 95V, if it matters.)

I've read a few opinions online that it's better not to use a bypass humidifier with variable speed blowers due to it confusing the CFM sensor in the furnace, and that a powered fan style should be used instead. Is there any basis to this?

Also...the temperature-based humidity control seem to turn the humidity way down with low temperatures. At -20F they're dropping the humidity down to 15%. That's crazy...you may as well not have a humidifier. Health Canada recommends 30% humidity at low temperatures. Also, with high quality windows and well insulated walls condensation is less of an issue. Are there any temperature compensated humidistats that let you set the minimum to more reasonable values?

Thanks,

Chris

[Tony Hwang]

Hi, Auto setting humidistat is no good for our climate. I am in Calgary. I have a Aprilaire with manual humidistat. If you set it at 30% on a day like today(25C tonight) your windows will all fog up. The more air tight the house the worse it'll be. My house is built on R2000 spec. About your concern for furnace I don't know. Armstrong is second tier. Lenox. Ours is Carrier.

[ransley]

The auto tracking April Air is near a mandatory feature to keep optimal humidity and prevent condensation, high humidity leads to mold, then wood rot. Do you have an accurate humidistat, digitals ive found to be more accurate overall, analog dial I can say from my research all need calibrating. Even my Taylor states I need to calibrate it every 6 months, and when I go to any big store display models vary 15% right in front of you, so you never know what you are buying. 30% is not good if your glass condenses and drips water, im sure Health Canada has that fact somewhere higher in priority then a humidity %. You can adjust the set point of the april air higher but you will be dripping water off the glass and ruining your house and maybe health. The key to proper auto tracking it to set it to condense on glass, then back off until just condensation stops and leave it there, Maybe April Air and Armstong could help but I think if its installed right it will work.

[trader4]

In addition to what others have said, it's not true that the auto tracking drops the humidity down to 15% at -20F. That is the RECOMMENDED setting for the Aprilaire units.

You get 15% at -20F with the dial set to 5, but you can set it all the way up to 7 if you want. Their table doesn't go below -10F, but the spec is that it drops humidity 1% for every 2F drop in temp. So, using that and the fact that the table shows with the dial set to 7 you get 30% at -10F, then you'd be getting 25% at -20F. I seriously doubt you want more than that. With it set too high, you get condensation around windows, recessed lights, etc which even in the short run can cause paint to peal. In the longer run, even more serious problems are possible.

I prefer the fan powered units over the bypass models, but to each his own. I have the Aprilaire 700 and am very happy with it. Many of us here have experience with them and found them to be excellent units. Simple to maintain, trouble free and reasonably priced.

[Tony Hwang]

Hi, Auto tracking feature does not work well when outside gets real cold like -35C and WC of -50C or so. That is why I disconnected it and manually setting humidity in the house. Our Prairie climate is extreme cold and dryness in winter. Ever saw a RH registering negative number?

[ransley]

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RH register a negative number? I believe that is impossible. Is that a analog dial type of humidistat giving you that reading. Analog units need regular calibration, analog dial units sold to consumers at hardware stores are not accurate through the range, most sold cannot be calibrated and are innacurate new, most cheap digitals are better or get a analog unit that can be calibrated or a Psychrometer. Once I took my calibrated unit to Menards, about 20 different taylors on display were all 5-15% off, I bough a big taylor that the instructions stated to calibrate every 6 months by covering it with a very damp rag for maybe 1/2 hr.

[Chris Friesen]

It should be impossible. I suspect that his point is that at extremely low temperatures the temperature probe included with the thermostat may not behave linearly.

Chris

[ransley]

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Because its not properly calibrated or it is defective is the correct answer. Often even cheap units can be calibrated, open it up so you can see the coil and see if it can be moved, then look up a calibration procedure, mine is cover with a wet very damp rag for 30 minutes and set to 93% . Im not kidding, store items are often 10-15% off calibration new before you buy them. I tested them before I found one I could calibrate, its a 3" round aluminum Taylor. Many home Thermometers are the same way, off up to 5f new in the box. Next time you go shopping read a display group, you will realise maybe none are set right and you cant know which one. I also calibrate thermometers because they are not attached to the proper point, I need have my self calibrated units, to heat apartments and keep from getting violations, also look at the accuracy of electronic units, often they give 1.5+ - accuracy, That is 3 degrees, to much for me.