Installing outdoor reset thermistor in air intake

TonyS

I have installed these on April air humidifiers but was wondering if anyone has done this on a boiler? Sometimes it can be a pain finding an area out of the sun.. any pros or cons to doing this?

HDE

Not good

Not advisable

Humidifiers only work after the furnace is operating thus outdoor air is drawn across the sensor.



If the sensor for ODR is in the pipe located in a conditioned space it won't read proper temp and likely stay in warm weather shutdown.

JohnNY

You mean the makeup air into the room?

I do it all the time providing there's a constant inward flow of air.



It's not ideal, but in attached NYC townhouses and multi-family buildings, often there is simply no better place to put the sensor.



The outdoor air reading may be off by off 2 degrees or so, but it'll work fine. I promise.

HDE

?

I'm positive he's asking about installing it in the boiler PVC intake pipe, knowing aprilaires instructions



If boiler hasn't run it won't sample outside air

TonyS

I am talking about the PVC intake

But I dont need to activate the warm weather shutdown and I could set minimum water temp above 75. I believe the resistor on the TT is 10k and can probable be replaced with the aprilair unit.. The aprilaire unit is designed to fit into a small hole drilled into the air intake and a clip to hold it.  I will check the k value and if it is compatible I will try it on my TT in the shop. I will let you know what my results are.

JohnNY

Oh!

No. You can't do that. You,d need a constant draw from outside or it won't work. 1

TonyS

Im thinking that

if the thermistor is in the pvc and the unit is idle, the controller would reset the temp to whatever temp it is in the pvc,down to my minimum water temp setting. But as soon as there is a call for heat and the tt terminals close, the inducer would start and cool the thermistor before the ignition stage even fires. By the time the boiler starts to produce heat the outdoor reset should be stabilized. Maybe I am missing something here but it seems as though it should work fine. What problems do you think could arise? The warm weather shutdown was something I didnt think about but most single family dwellings I wont use that. I let the customer decide when they want heat. Even if they want heat just to a towel warmer or to take the chill off tile on a warm day. I am just looking for options because some of these large semi city homes I dont have access to a north wall and the last one I did I must have spent 3 hours getting that outdoor stat to a suitable location.

heatman101

Never thought of that...

however, I think you will find that the sensor will not react quickly enough...and the boiler may cycle off before it cools the sensor to the correct temperature.

It really would not be hard to experiment a try it...bet you will find that it really don't work so hot though...



But hey... if it does work, let up know...

JohnNY

I don't like to answer questions with an opinion...

...but I do think the rapid changes in temperature between the boiler being idle and still connected to the heat exchanger and the drop from the incoming air will do nothing good for the reset curve.



That said, I'd love for you to try it and let us know how it went.

Mark Eatherton

I don't know....

Depending upon who's boiler, it cold create more problems than what its worth. When the boiler shuts down the burner, residual heat could rise up back through the combustion air pipe, causing the logic to go off on WWSD. Until all residual heat is dissipated, you could be locked out by the fickle finger of fate.



I have used the C/A pipe as a chase to get the sensor located outside...





ME

Ironman

This One Definitely...

Deserves the definitive hydronic answer: "it depends".



If the c/a pipe is a long horizontal run with a goose-neck, or if it connects directly to the gas valve, and if the sensor is placed in the outdoor portion out of the sun, then maybe it could work. Otherwise, I'm skeptical too. But, I am curious.



Give it a try and let us know.

gennady

outdoor sensor

I was thinking about it , but never done it. I think, if sensor is installed right in the inlet fresh air elbow, it might work, is it will be in the shadow and read actual outdoor air temperature without influence of sun, walls, windows and others sources of heat..  

TonyS

8 days without electric

Sorry I didnt get back to this thread. I lost electric 8 days ago in that freak storm and I was last on the list to get turned back on. I will try installing the thermistor as soon as I get caught up and share my results.

I learned alot about generators in the last few day though.