Kuuma VF100 arrived

[JRHAWK9]

This may (or may not...lol) help some of you guys. Like was mentioned before, I have thermometers placed in my cold air return (at the blower box) and in my supply plenum. I monitor these just for my own sanity and to get a grasp on what's all happening and help me improve things if possible. My cold air is not tied into my existing cold air because I want to have the ability to run both the wood and LP furnaces at the same time and you can't do that when they share the same return. Therefore I use a centrally located open stair case for my cold air. Up until last night, I didn't have any ducting attached to the blower box, it was just an open filter with it sucking in air off the basement floor.

Anyway, in these sub zero temps we have been having, I noticed my cold air temp at the blower box were running ~5° colder than the house temp upstairs. I did not remember noticing this back when the weather was not quite as cold. I also noticed the temps near the ceiling of the basement were consistently hovering around 80°+ as long as their was a fire in the furnace. Even when the fire is at the end of the burn cycle and there's just coals left, the temp at the ceiling was still mid 70's in these sub zero temps.

So, what I did was box out and raise the intake of the cold air to almost the bottom of the TGI rafters. It's 16"x18" and about 6' in height. I'm now pulling in much warmer air and hence my plenum temps have noticeably increased.

Last night it was -4° at 9:30pm when I went to bed after loading it up with 70lbs. It was -6° at midnight and when I woke up at 6:30am it was -9°. The house was 68° at midnight and 67° when I got up in the morning. The blower was still running when I got up and there were plenty of coals in the furnace 9 hours later. I even had the blower on high the whole night, which I could never do before because the plenum temps would get too low.

I'm now going to play around with my SP's again to see if I can drop my supply SP a bit seeing I raised it last winter in order to bring my plenum temp up some. I believe right now my supply SP is +0.22" with the fan on low. Would be nice if I could increase my CFM w/o decreasing my plenum temp much. I'm also guessing, with the addition of the new cold air duct, my return SP also increased a bit even though it's 288 sq inches and only ~6' in length.

Keep in mind, this house used to use ~1300 - 1500 gallons of LP a year......so it's not the most efficient to heat LOL

Anyway, I would have never noticed this if I didn't have thermometers placed to monitor temps. I believe doing so really helps in getting your system dialed in.

 

[brenndatomu]

So, what I did was box out and raise the intake of the cold air to almost the bottom of the TGI rafters. It's 16"x18" and about 6' in height. I'm now pulling in much warmer air and hence my plenum temps have noticeably increased.

Hmm, I may hafta try that, wouldn't be too hard. After all, my Tundra heats the furnace room better than any other room in the house

 

[buckdroppings]

I can't tell you how helpful this thread has been in helping me decide what to do in my home. My wife and I have been remodeling our home for about seven years, ranch on a basement. We installed a new LP furnace upon purchase to replace the original that came with the home. We primarily heat with a homemade wood stove in the basement which could not be more dirty and inefficient. I've looked at the Kuuma for a couple of years but haven't been confident enough to move forward. We recently started to rearrange some of our remodeling to include a zero clearance fire place on the first floor, for looks and better heat. Yesterday I reminded myself about the Kuuma and started looking up info again. If I can figure out how I can get a chimney ran from where I have to put the Kuuma it will be a done deal. There will be no zero clearance fire place.

 

[JRHAWK9]

Here's my static pressure numbers. I have a 24"x10" duct connecting the plenum (24"x24"x39" tall) to my existing 20"x10" main trunk line. Up until tonight, I had a 3.5"x24" "restrictor" placed in my 24x10 duct in order to increase static pressure. This gave me a supply SP of 0.17" or so. If I don't run any type of restriction, my SP is 0.11". Tonight I trimmed the restrictor to 2.5"x24" and my SP dropped to 0.15" or so.

This is where I'm currently at:
Low speed blower: return SP is -0.13" and supply SP is +0.15"
High speed blower: return SP is -0.17" and supply SP is +0.22"

I'm going to see how these work. Don't know if these are good, bad or indifferent, but that's where they are currently. Thought I'd try a bit less supply static pressure for the added CFM.

Comments?

 

[JRHAWK9]

Hmm, I may hafta try that, wouldn't be too hard. After all, my Tundra heats the furnace room better than any other room in the house

Another thing you may want to look at is sucking some of the heat off the face of the furnace into the cold air to help increase the temp a bit more.

I tried this last night with a couple runs of 4" drier vent just to see how it works. I placed one end near the face of the furnace and the other end inside the return air "box" just upstream of the filter. It definitely increased the temp of the return air entering the furnace. This, in addition to raising the height of the return air intake, not only increases the temp entering, but also seems keep the temp of the return air more consistent during the end of the burn. At least in my house it does seeing in cold weather the house seems to drop when the fire starts to die out. Keeping the air entering the furnace consistently warmer seems to greatly reduce the snowball effect at the end of the burn. By snowball effect I mean when return air temp decreases which in turn decreases the supply temp which decreases the house temp which starts the snowball effect.

We've had a warmer spell yesterday and today, but this weekends forecast as of now is -15° Sat night, a high Sunday of -8° and a low Sunday night -15° and a low Monday night -11°. I'll have some time to see what difference it makes. One thing to note, I haven't noticed any real difference in basement temp by doing these two things either. The furnace room is still 75°+ while the rest of the basement is high 60's.

 

[DaveH]

New 24X8 return put in this weekend. Furnace runs completely different. Outside temperature high has been in low 20s and the house is 70-72 without issue.

To compound the issue of too small duct work, the craftsmanship was horrifying. I am the second owner of the home, and I wish I knew who did the install so I could warn others.

The oddest portion is at the very end of my supply there was a run of flex duct. I'm told the end needs to be capped in order for pressure to build throughout the trunk, strike 1. To make it worse the flex T's and ties into two registers. I ripped the extra section of flex off and found it wasn't even tied together in any way. A 4 foot piece of flex was taped to the side of another piece of insulated flex duct, no metal T, no hole, just taped together, flex duct taped to foil cover. To pass inspection or they just got lazy I'm guessing. I never thought I had to disconnect the duct work connections to ensure they actually moved air.

 

[STIHLY DAN]

Keep in mind all supply ductwork needs to be metal.

 

[DaveH]

Keep in mind all supply ductwork needs to be metal.

The flex duct is disconnected and being replaced. I understand that manufacturers don't want flex duct, but this was almost 40 ft from the furnace.

 

[STIHLY DAN]

That's good to hear. keep in mind during a power outage 40 ft away still gets very hot. I have seen/tried it.