Everything Drolet Tundra - Heatmax...

brenndatomu Posted By brenndatomu, Feb 8, 2015 at 9:42 PM

  1. JRHAWK9

    JRHAWK9
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    In those cases where one does not have large enough supply ducts to support the sheer volume of air two blowers running simultaneously will put out, I would agree. This sounds like the issue you would have.
     
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  2. Kdc88

    Kdc88
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    Hello everyone. New here, ive read a lot of stuff on this thread and its all very good info so thanks to everyone. I bought a tundra df02000 the day i purchased my home. I just got around to installing it this year before winter. I have it installed and everything is correct as far as clearances go. I have no cold air return hooked up yet and i put dampers in the supply ducts to get the static pressure that the manual calls for. I have no draft issues, that works great, no modification needed. Ive been running it for a few months now and this thing is doing nothing but eat all the unsightly fore wood in the basement. I will soon be hooking up the cold air return and putting in a combustion air pipe to the outside but i was just wondering if you guys might have any suggestions. It cant even get the house above 60 seems like a very large waste of time and money so far. If i cannot figure it out i will be selling it for a different brand but id rather not if i dont have to. Any ideas or suggestions would help thatk you. I will post pictures tomorrow of the setup if needed.
     
  3. sloeffle

    sloeffle
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    If I had to do it over, I would buy manually weighted dampers. I would make running both furnaces a little bit easier.

    Live and learn......
     
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  4. maple1

    maple1
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    If the return isn't hooked up - isn't it pulling in cold air from the basement floor? Which is likely quite cold?

    Also if it is anything like where I'm at - it's likely pretty cold outside too? Maybe some of that cold outside air is getting sucked into the basement since the return is pulling from there?

    Not knowing anything about the house - maybe it's doing pretty good doing what it's doing?

    Having said that - there are more capable furnaces out there. We just don't know much about your situation.
     
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  5. JRHAWK9

    JRHAWK9
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    This was my original plan and how I had things setup when I first installed it. I had my powered damper wired to close when the LP furnace ran regardless of what the wood furnace was doing. I had the LP thermostat set at like 60°. My thought was by the time the house reached 60° the wood furnace would be cooler and the blower wouldn't need to run anyway. This was back before I had made any tweaks to my supply/return air and things were FAR from being optimally setup. Looking back, my original return/supply setup was terribly inefficient. The furnace was always burning and making the BTU's just fine, I was just not getting them into the house very efficiently. Anyway, it just took one below zero day to realize I needed to find a way to get both furnaces to work seamlessly together so I could set the LP thermostat at like 68° and not have to worry about it.


    I used to pull the cold air off the basement floor and this is one of the changes I made as referenced above. I boxed out the return air and brought the intake up to the basement ceiling so it would be taking in the warmer air off the ceiling instead of the cold air off the floor. I then made a duct system which reclaimed some of the hot air radiating off the face of the wood furnace and injected it into the cold air. Doing this basically just increase what they call the "delivered efficiency". Contrary to what I thought may happen, the basement still remained heated just fine. A few days ago I took some sample temperatures. It was 0° outside when I did this. The temp of the air on the basement floor was ~65° at the rear of the wood furnace. The temp of the air coming into my return air "plenum" sucking from the basement ceiling was 73°. The temp of my return air inside my blower box after being mixed with the reclaimed air off the face of the furnace was 86°. Those two mods made a 20° difference in the air I am taking in and sending through the air jacket to get heated. My cold air temps are always anywhere from 80° - 89° depending where I am in the burn cycle and how high I have the wood furnace turned up to. Most of the time they are in the mid 80's.

    The reason I'm telling you this is, try to get your cold air intake off the basement floor. It should increase your supply temps with very little affect on the heated basement temps. At least in my experience anyway.

    Also, I firmly believe that any warm air wood furnace, regardless of brand, can benefit from taking the time and experimenting with return/supply air. I found out by simply adding the blower controller to mine that my house LOVES low volume/higher temp supply air. I have my blower slowed down quite a bit to the point I really can't go any slower with a sleeved bearing motor. Every time I slowed it down more I saw positive results.
     
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  6. joes169

    joes169
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    How warm is the basement getting?

    There's certainly a lot of fine tuning involved in getting these things, or any wood furnace, to operate correctly, but not having a cold air return hooked up is pretty much a recipe for being let down. 4 years ago, when I hooked up my Caddy, I ran a day or two w/o the return ducts hooked up, and I was also let-down and thought I made a mistake. Once you get the system complete and tweaked, you'll be much happier.
     
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  7. DoubleB

    DoubleB
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    Welcome Kdc88!
    Agreed there's probably something else yet to be done with your Tundra but I can't tell enough info from your posting. I'm only one datapoint, but through this cold and wind our Tundra has single-handedly heated our leaky poorly-insulated farmhouse, 2100 sq ft living plus 1050 sqft basement. Granted, that took some babysitting and frequent feeding, but without overheating or over-running the furnace beyond normal.
     
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  8. KC Matt

    KC Matt
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    That's insane. Something is really wrong to use that much wood unless they are heating a warehouse.

    I'm more convinced by the day that having separate ductwork is the way to go. In my case adding the second run would be very difficult, but if I could manage a couple of supply runs, the two furnaces could share a return duct in my mind. When the gas comes on, the Tundra is cycling on and off of low speed and the two would be pulling the same direction. There is just no good way to install the duct runs.
     
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  9. JRHAWK9

    JRHAWK9
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    If you want the ability to run both at the same time, I would not share return ducts, unless they were sized accordingly. They would be fighting over return air otherwise and one may be "robbing Peter to pay Paul", especially if one blower is turning slower or is weaker.

    This is the exact reason why I added a relay to move power away from my blower controller (controlling high speed tap) to the low speed tap on my wood furnace blower as soon as the LP furnace kicks on. While I was testing how the furnaces played together towards the end of a burn, I noticed because the controller had slowed down the wood blower so much, when the LP kicked on it actually started to backfeed the wood blower. Not cool. So the way it is now, as soon as the LP kicks on, the low speed winding becomes active and now there is no back-feeding.
     
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  10. joes169

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    This is only my opinion, and to be clear, I don't own a Tundra but the similar Caddy, but I don't want my LP furnace and Caddy running at the same time. I just set the LP furnace back a few degrees below the Caddy t-stat and live with the fact that I'm burning a minimal amount of LP when I'm too lazy/not home/able to add wood.
     
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  11. JRHAWK9

    JRHAWK9
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    So, when your house temp drops a few degrees to your LP thermostat setpoint your Caddy blower stops? At the end of a burn on a very cold morning when the wood blower is cycling and the house temp drops to your LP's temp setpoint, what keeps the wood blower from cycling when the LP kicks in? I can see setting the LP thermostat like 10° under the wood one, but I'm not sure only a few degrees would be enough. Unless your home is crazy insulated and can hold heat long enough for the wood furnace to pretty much go cold before the house drops 3°.
     
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  12. laynes69

    laynes69
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    Our woodfurnace is usually set at 74 overnight, but in this weather, I set it at 72. We keep the LP set at 68 and the central furnace never runs. Some time this week, our LP was set at 70, and this morning I woke to a 70 degree house (chills at -15, temp below zero) and our central furnace never ran. We have manual dampers and the LP side was never tripped.
     
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  13. joes169

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    There's a ton of variables, but yes, I set it back about 4-5 degrees typically. If the Caddy blower were to run for 20 seconds, I'm not worried about it much. Odds are the furnace may not be running at the same time anyways. My house is not super insulated, but it certainly takes a LONG time to see a 10 degree drop in temps, especially when the Caddy is loaded full before bed.

    I should also mention, I have mine set so the blower won't kick on until it reaches 150 degrees, which is more than just a little coaling.
     
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  14. KC Matt

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    That's interesting. If we suppose the gas furnace blower overpowers the wood furnace (it should) then air is still flowing through the heat exchanger of the wood furnace it's just going backwards. I've seen just that when the wood furnace was dying out and the gas furnace kicked in. The output was far warmer than what the gas furnace produces by itself. When the wood furnace is producing little heat, what difference would it make if the air flows backwards through the heat exchanger?

    What I am trying to avoid is having the output of the gas furnace cycle through the wood furnace instead of going through the house. In my mind that wastes energy and jeopardizes the gas furnace heat exchanger. The other issue to me is having the output of the wood furnace circulating through the gas furnace. The heat exchanger of the gas furnace absorbs heat while the house gets cold.

    Seems like a couple dampers would make it work. Everything is a compromise here, including the ability to install the ductwork. Doing so would mean tearing out a finished basement here. Maybe $10,000 plus ductwork.
     
  15. JRHAWK9

    JRHAWK9
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    As far as what backfeeds what, that all depends on the motors and what speed taps are being used. Backfeeding anything is not a good idea, IMO, as you are going against the direction of which the blower is rotating and are also now running heated air over the blower, which reduces the cooling.

    I can't speak on your install, but I avoided the LP furnace backfeeding the wood furnace by a power close/spring open damper in the duct connecting the wood supply to the main supply truck of the house. I avoided the wood furnace backfeeding the LP furnace by a simple gravity damper in the plenum of the LP furnace.

    I just wanted to make sure my system was setup to automatically deal with any combination of events which may occur. Some may consider it overkill, but relays are cheap and are easy to wire.
     
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  16. TDD11

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    I agree that my ducts just aren't large enough to support multiple blowers.

    How do you account for a power outage? I would think that setup would reduce the heat rise through the stove during a power outage.

    Exactly my thoughts. Still mulling over ideas as far as how to run the ducts if I go through with this. I may have a HVAC contractor in soon, as soon as this cold temps let up and their work load reduces. Like I mentioned, the worst part of this setup would be the trunk duct running through the basement below the floor joists.

    Here's a basement picture showing the actual setup.
    20180103_111519.jpg
     
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  17. brenndatomu

    brenndatomu
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    Just FYI. Most blower motors are only rated to operate in 100-105*F ambient air...max...so backfeeding = bad
     
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  18. JRHAWK9

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    I don't see it any different than having the cold air tied into the main trunk. The vertical rise when doing that is even more than just going to the basement ceiling. The furnace is UL listed for gravity flow. The manual mentions just removing the filter to aide in airflow.

    yep, I know I looked into this when reclaiming radiant heat. I wanted to make sure I was not exceeding the temp it was designed to run in.
     
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  19. JRHAWK9

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    Have you tried it and measured your SP?

    You could always check your heat rise on your LP furnace and potentially use a different speed tap on the LP motor to slow that down some as long as it still remains in the range as stated on your furnace's data tag. You'd be gaining efficiency in your LP furnace if you could go down a speed tap or two and at the same time decrease the volume of air coming from the LP furnace. This may be enough to allow you to run the two blowers simultaneously. I was able to go from using the medium-high speed tap to the low speed tap on my LP furnace and still stay in the middle of the heat rise range. Doing this allows both blowers to run on low and still only see a SP of 0.4" even with 5 out of my 13 registers closed during winter (3 downstairs and 2 in the loft I keep closed all winter).

    You could then simply put a gravity damper in the plenum of your LP furnace and call it a day.
     
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  20. KC Matt

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    There may be a powered damper solution that would work in my setup. Honeywell makes an ARD-6TZ powered round damper that can be normally open or normally closed and a rectangular ZD14x24TZ. The rectangular damper appears to fit within the 14x24 footprint which is the only way for me; there's no room for overhang.

    Now the problem comes when the house temp is dropping at the end of the burn, but the Tundra is cycling on and off, so is the gas furnace. You would have to somehow ensure the Tundra could unload it's heat so would you adjust the dampers to allow some flow in the closed position? Maybe set up a relay that allowed the Tundra to open one of the 6" dampers when the fan comes on regardless of the gas furnace?

    It would be so much easier to have separate ductwork but it's not in the cards for me.
     
  21. JRHAWK9

    JRHAWK9
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    Not a problem at all. Simply wire up the dampers, via a relay, to be closed only when the LP furnace is the only unit running. All other times they will remain open.

    The wiring below assumes you have a 120Vac EAC (electric air cleaner) circuit on your LP furnace's circuit board you can connect to. It also requires a POWER closed/SPRING open damper. You don't want a power open damper as in a power failure it would remain closed. This is how you would wire it so the only time the damper would close would be when the LP blower motor is the ONLY unit running (in both heat and AC modes). All other times the damper(s) will remain open, IE. when the wood furnace blower circuit is active, both LP and wood furnaces blowers are active or if there's a power failure.

    Damper Wiring.jpg
     
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  22. KC Matt

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    Looking at the system, it appears that only one damper needs to be closed at a time. When the gas furnace is running, the return duct must be open, while the wood furnace supply must be closed. Conversely, when the wood furnace is running, the return damper must be closed and the wood furnace supply must be open.

    So when the gas furnace is running and the wood furnace is running, the return side must be open, but, depending on the interaction between the two blowers, at least one of the supply dampers from the Tundra must be open. I would guess that when the Tundra blower is on the 3 tap both dampers would need to be open while on the 1 tap one damper would be adequate.

    Add another complication: I have an insert in the basement and plan to use the blowers of the two furnaces to help distribute the heat from the insert.
     
  23. JRHAWK9

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    Oh, so your wood furnace IS hooked up to the house's return air duct then? If so, I would not recommend both furnaces be running at the same time if they share the same return duct.
     
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  24. sloeffle

    sloeffle
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    I agree with you one-hundred percent @JRHAWK9. Both of my furnaces are hooked into my return ducting and I cannot run them both at the same time. There is not enough return air. The few times I have them together I will take the back off of the wood furnace so it pulls in the air from the basement.
     
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  25. sloeffle

    sloeffle
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    Finally put the Caddy to bed last night and fired up the geothermal furnace for the first time in at least 3 weeks. Generally I only run the wood furnace when I get home from work if temps are <30 or so. We will run it 24x7 on weekends if the temps are low enough. Even though we have had it for 5 years I am still a little hesitant on running when I am not home. During this long cold snap I'd say I have burned around 1/2 a cord of wood or so. We generally burn around 2 cords a year. Temperatures in house were generally between 65 ( early morning ) and 72 ( mid-afternoon ). One morning I woke up and the house was 63 but that was my own fault because I let the furnace go for 11 hours without a refill with outside temps around 3 - 5F.

    I am glad to see the cold snap come to an end. It is supposed to be 54F here on Thursday. :)
     
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