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Discussion Starter · #1 ·



[some beautiful pictures](https://imgur.com/gallery/q8m6Ol8)

first time posting apologies if my placement is off

I am debating between two units, venmar evo5-700 which doesn’t support furnace interlock or lifebreath rnc205, which does support furnace interlock. Based on my duct setup (simplistic) I would likely need interlock. I am in Canada and during winter the house gets humid during winter, tons of frost on windows.

Ill will include as many pictures as I can, including a visio drawing.

The setup has a fresh air intake, others have indicated there is likely an electronic controlled damper, however I know on the fresh air intake there is only a manual damper, it is currently visible near the furnace and I do not recall a damper along the duct while I was drywalling the basement.

Upstairs we have an ecobee (pictured) which controls furnace, ac and humidifier. And a ventilation switch which controls the furnace fan and the bathroom fan.

Downstairs, I have traced most the wires, the vent switch goes to a junction box labeled “MUF” which goes to a transformer and then a relay (G7L-2A-BUBJ-CB) and then to a switch (RIBX24SBA) near the panel which is set to closed, which means on, I tested with multimeter. This switch controls a 14/2 wire which I now know goes to the hood range fan plug in the kitchen. Which makes no sense because you wouldn’t be able to turn on the range fan without the vent switch on.

As well there is a junction box labeled “cold switch” this has power from the panel to the furnace, as well a another 14/2 wire which is wired backwards (black on white from power and black on black to furnace), no idea where this wire goes or if its relevant.

Finally, there is the random 3 wire low voltage wire dangling that I assume comes from the same wall as the ecobee, I have not confirmed this but based on ducts and location It would be possible to rout new wires to basement from ecobee/vent switch wall.

I know this is a lot of information, essentially, I just want to install an HRV unit and want to wire it the best way possible. Ideally it would be controlled through the ecobee but I gather I can not control a second device (on top of my humidistat). I know you can get digital control panels for hrv’s, which again I could setup on the same wall, though it would be nice to replace the current vent switch, the problem being it is running 14/2 wire so I would need to get a receptacle switch which may not have all the programable features, maybe a timer. It would be nice to wire it to turn on whenever the furnace turns on, then I could set the ecobee to run the fan every hour or so, not sure if you are supposed to do that. Though I think most set the HRV’s dynamically, so they push out moisture in winter and don’t run them in the summer except for fresh air intake. In my case I know I would need it running lots in winter.

TL/DR; ambitious person in lockdown procrastinating on schoolwork by installing an HRV, confident in duct work but no idea how I should wire the thing.
 

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The manufacturer's control will always do a better job of controlling the hrv than the ecobee. The ecobee can only turn it on and off.


The interlock turns the furnace fan on when there's a demand for ventilation.

I would not do a simplified install and interlock the furnace. Running the blower motor to distribute like 100 cfm of ventilation air is very wasteful especially if you have a psc/inefficient blower motor.

Interlocking the other way, only allowing for ventilation when the furnace will render the hrv ineffective in the spring and fall, when ventilation is required most.

When it's brutally cold and the furnace is running a lot, the natural stack effect is strong and if anything houses get too much air exchange. HRV may not need to run.




Take the stale air from a suitable room in the house and dump the fresh air into the return.
When the main blower is off, fresh air will find its way into the house from the return.
 

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Discussion Starter · #3 ·
Thank you,
I basically have to do the simplified instal as the house is finished, however I could run the stale air intake down the air return a few meters.

when you say:

Interlocking the other way, only allowing for ventilation when the furnace will render the hrv ineffective in the spring and fall, when ventilation is required most.
do you mean because the heat/ac doesnt normally run? i could program ecobee to run certain amount of time per hour
 

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Yah - equipment won't run enough.

I don't recommend using the main blower to circulate ventilation air without heating/cooling unless you have an ecm motor.

Can you take the stale air from the basement - like put a hrv return outside the furnace room and put fresh air into the return?

If you end up with a simplified install, best to use the hrv's proper controller and set it to ventilate like 20 minutes each hour or something and have it bring on the furnace fan.

There are different modes and some controls have a minimum setting - like 10 or 20 minutes of ventilation on low and it jumps to high and runs all the time in the heating season when the humidity is above a certain threshold.

The ecobee may be able to do something similar, minus the fan speed control. You'll have to see what settings it has available. Won't be as good as the manufacturer's control.

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If your furnace has a regular blower motor and is in good shape, not too old - it may make sense to retrofit it with an ecm motor.

The ecm saves 30-50% in heating/cooling modes and on low speed continuous fan (hrv interlock) uses 60 to 70% less.

There are 3 retrofit products that I know of, they start at $200 and go up to $400+ us.
 

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Discussion Starter · #5 ·
thank you,

this is the furnace motor is thats what you are refering to when you say ecm motor, I cant tell if its ecm



https://imgur.com/gallery/MCZJgQo

model is: ydz-040l22541-01

i could run the pipe from the hrv to a wall with a return directly behind the furnace, or shove it several feet down the joist bay ducts (sorry for poor terminology). I was trying to see if any of the registers had a straight path to the furnace room but I don't see any way to pull a duct significantly further from the furnace.
 

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The picture is of your inducer motor, not main blower.


That's a condensing carrier furnace - that style had a lot of secondary heat exchanger problems and if it's 10+ years old, it should be checked. search this board for more info.


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Is the furnace in a basement?


Can you take stale air from the room above? A 4x10+ to 6" round register boot would do the job.
 

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Discussion Starter · #7 ·
Is the furnace in a basement?


Can you take stale air from the room above? A 4x10+ to 6" round register boot would do the job.
yes and yes! never thought of that, the rool above, even thugh its right above the furnace, if i use a boot it wont circulate in the hrv. Thank you

As far as wiring it, should I still interlock? since it would be more airflow?

and any opinion on the two models? evo5-700 which doesn’t support furnace interlock or lifebreath rnc205
 

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I'm not familiar with individual models.

If you avoid the ones made for builders and get one with all the features desired, should be okay.

Do consider repair costs - ie there are units with ecm motors which could cost a fortune to repair. ecm for an hrv may not ever pay for itself.

As far as wiring it, should I still interlock? since it would be more airflow?
It's not really necessary. If the hrv will be in the furnace room, you can do it later if required.

I still have that ventilation switch upstair which just turns on furnace fan and bathroom fan, not sure if I could have that manually activate hrv?
That switch will be rendered obsolete.

I would get a wall control that control run time each hours and speed plus cycle to high if humidity is too high. A lot of them are the size of a light switch - would need a separate box as you shouldn't combine low and line voltage together.

You can get a separate push-button control to manually activate.

Just make sure the controls are compatible with the unit.
 

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Discussion Starter · #11 ·
Oh and one more thing, i just realized I bring in stale air from the register behing the furnace, still in basement, or main floor. is there an advantage to going higher or lower? ie main floor vs basement
 

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Main floor makes most sense - more moisture and co2 production.

"Are they saying setup some relays so they can not be active when hrv is running?"

No - just when balancing, exhaust fans shouldn't be running.

Balancing needs to be done after the unit is installed - means making adjustments so the exhaust air volume is equal to intake volume. i believe you need a manometer to do it.

manufacturer should have specific instructions on balancing.
 
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