Drolet Heatpro

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If I reduce my duct work from 8 to 6 inch at the furnace how many 6 inch duct to I need to get to the 168.
Six. Or three 8" and one 6" will take you to ~178ish
f I open all the 6 inch hole that would give me plenty of air movement to keep the furnace fron over heating
If you open all the holes you will likely have to run your blower on high to get .2" static pressure. Then the blower will probably cycle on/off a lot. I'd only use the holes that you have to use to get the job done and still meet all the specs
 
Thanks for the information. I think I will run 3-8s and one 6 inch. I was just wondering if reducing my 8 inch duct to 6inch at the furnace would get me close to 168 sf and keep pressure at .2. Since my ceiling is that high I'm going to run use the full plenum. To test the plenum, do I drill a hole at the very top and use my manometer or just in one of the duct holes?
 
I was just wondering if reducing my 8 inch duct to 6inch at the furnace would get me close to 168 sf and keep pressure at .2
Hard to say, you will be losing CFM for sure though. I'd just open the holes up to accommodate 8" take-offs. If the factory holes are too close then I'd rivet/screw a piece of sheet metal over the existing holes, then cut 8"ers in.
To test the plenum, do I drill a hole at the very top and use my manometer
Sounds right to me. Someone jump in if I'm wrong. If you have a Dwyer Mark II model 25 manometer then you will need to move the hose to the other port on the top of the meter. Going from vacuum to pressure...
 
I just finished installing my ductwork yesterday. (I'll try to get a picture or two tonight) Wett inspection tomorrow and then I can spark it up.

I went with an 8x20" rectangular duct, (160 sq") and a single 8" round (50 sq") for a total of 201 sq".

Total Airflow is what's important to keep the firebox from melting down. As far as the static pressure anything LESS THAN 0.2 "WC, and any area MORE THAN 170 sq" should be just fine.

The only risk of going too big or two low of a back pressure is the firebox could cool off too much, and the secondary's won't light up. Given the HeatPro has a 4 speed fan and controlled by a thermocouple, and will dial down the blower speed when temps drop, I don't think this is an issue at all.

The same can NOT be said for the Heatmax/Tunda with it's snap switch. That's why only 2 of the 4 round 8"outlets could be used...
 
Well I look forward to seeing your pictures of the duct work. I plan on using 3- 8 inch vents that will run about 15 feet then 1-6 inch vent. The 8 inch will be adapted from 6 to 8 inch right at the furnace plenum. If each 8 inch is 50 and the 6 inch is 28 then I should have around 178 which is a little above what is needed. I didn't know the fan adjusted it self according to temp. Do you know what temp the probe is set at to turn the fan on and what stack temps will be?
 
Well if it burns anything close to a max caddy then I'd bet your going to love it
 
Well I look forward to seeing your pictures of the duct work. I plan on using 3- 8 inch vents that will run about 15 feet then 1-6 inch vent. The 8 inch will be adapted from 6 to 8 inch right at the furnace plenum. If each 8 inch is 50 and the 6 inch is 28 then I should have around 178 which is a little above what is needed. I didn't know the fan adjusted it self according to temp. Do you know what temp the probe is set at to turn the fan on and what stack temps will be?

Ummm no. That won't do. A 8" run connected to a 6" hole at the plenum ... ya that only counts as a 6". You need to cut your plenum holes out to 8" for that plan to work.
 
The 8 inch will be adapted from 6 to 8 inch right at the furnace plenum.
Ummm no. That won't do. A 8" run connected to a 6" hole at the plenum ... ya that only counts as a 6". You need to cut your plenum holes out to 8" for that plan to work.
Exactly. Think of it this way, if you have a 8" dog and you give him a 6" doggy door...:rolleyes:
 
Looks good, now that will get you to .2 or less? I plan on using 3 8 inch and 1 6inch pipe. Now a 8 inch pipe is 50. The book doesn't say, it does list a 6 inch at 28. What tool did you use to cut the 8 inch hole?
 
Tin snips for the round hole, and an angle grinder with zip cut for the Rectangular hole only because of the overlap of the adjustable plenum meant cutting through twice the thicknesses.
A = Pie x r x r
A= 3.1415 x 4 x 4
A=50.2 sq" for 8' round duct.

Keep in mind, if you are feeding with an 8" duct, you need enough registers to to vent "almost" the same area. (Manual says slightly less, but that can be dealt with register flaps or dampers to balance flows.)
You will need Two 6" round registers per 8" supply duct.

As far as the 0.2 duct back-pressure, well see after I get the fire going. I have a big system with long runs and lots of outlets so I expect it to be lower. I'll have to play with the dampers on each run to get my flows and static pressure dialed in.

The reason the manual wants your register areas to be "slightly less" than your feeding area is so the entire system pressurizes, and flows evenly out of each register. Too many registers just let the air escape out the closest registers to the furnace, and nothing gets blown out of the end of the runs. Lots of people have cold rooms on the far side of their house for just this reason. I restrict registers close to the furnace because that air is the hottest and lower flows are needed to heat the room.That builds the required back pressure of 0.2"WC to force air (now slightly cooler...) in higher volumes out of the furthest registers.

If I go too far and over restrict the registers, the static pressure will rise above 0.2' WC, and that will reduce the overall air flow through the furnace and overheat and damage the firebox. THAT's why the 0.2" spec. is in the manual.
 
If I go too far and over restrict the registers, the static pressure will rise above 0.2' WC, and that will reduce the overall air flow through the furnace and overheat and damage the firebox. THAT's why the 0.2" spec. is in the manual.
Isn't the static pressure spec also so that you are reducing the airflow past the furnace (heat exchanger) enough for it to raise the air temp a good bit, (and limit blower cycling on most wood furnaces) but not so much as to overheat the furnace as you stated? You want a balance of both, hence the SP spec of .2
A = Pie x r x r
A= 3.1415 x 4 x 4
A=50.2 sq" for 8' round duct.
Can also use diameter x diameter x .785...easiest for me
 
My ducts will be 8 inch. One is about 24 feet long,], 2 are going to run about 15 feet. 6 inch about 5 feet. They do not reduce in size because my house is very open. One for the main floor, one for the basement, one for the converted garage and the 6 inch for additional heat in the garage, On the shorter runs I will be able to restrict the air flow with a register. I will check the static pressure to make sure it is right. I used this set up on the tundra and never over heated it so I'm hoping it will be the same on the heat pro. Today will be the fist day that I fire it up and burn the new paint off it.
 
Well burnt it off to day. I have a couple of questions that maybe can get answered. What is the small digital meter in the back of the furnace for and is the fan a variable speed fan that adjust by it self according to the heat?
 
Well burnt it off to day. I have a couple of questions that maybe can get answered. What is the small digital meter in the back of the furnace for and is the fan a variable speed fan that adjust by it self according to the heat?


We were hoping you could tell us that stuff ;-) I think the fan speed adjusts itself depending upon heat level detected by the supplied RTD sensor - but that is just speculation based upon what I saw in the manual. I didn't see any references to a small digital meter in the manual - was it factory supplied or are you talking about something you saw here on the forum that someone added to their furnace?
 
No the digital meter or what ever it is, is on the back of the furnace. It could ne a error reader that displays if you have a problem or maybe to set the probe temp. Not sure but its no in the book that I could see.
 
Made a pan View attachment 461063 View attachment 461064 one 12 inch should be two 6 inch. Been working good getting nice secondary burn .
You mean equal to two 8"? It is, actually a hair more 100.5 sq in for two 8" vs 113 sq in for your 12" pipe.
I did something similar on my sisters Tundra, only it is taller (more like a regular plenum) and has (4) 7" round ducts coming off it. Seems to work fine
 
Like a 6 / 12 roof is not half of a 12 /12 roof numbers are crazy. If you want a big shot gun the smaller is bigger . If you want to play in the garden you half to know the rules !
 
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