Losing 50 degrees!

[AOD]

I got my Silver Star add-on hooked up through a roundabout means with a long 8" duct meandering through my cold crawl space about 25 feet. My output temp at the big register is only 93 degrees! So I took a digital thermometer and made some readings. At the duct outlet, about 4" above the furnace with a medium sized fire burning I am reading over 140 degrees, my thermometers range ends at 140, so I am going to guesstimate it's 145. Down in the basement at the point where my duct connects to the cold air plenum I am only reading 94. So in that 25 feet I am losing over 50 degrees! Would duct wrap make a significant difference? All this heat is going to the crawl space, which is kind of good because it keeps the pipes warm, but I can't get the house over 67! Im thinking of wrapping part of it and seeing how it works.

 

[laynes69]

Yes I would insulate the duct. Also try not to have but few bends if needed. The straighter the shot the better. Never heard of that kind of furnace.

 

[AOD]

Yes I would insulate the duct. Also try not to have but few bends if needed. The straighter the shot the better. Never heard of that kind of furnace.

Let me count the bends I have......between the furnace and the cold air plenum ... theres 6, in the cold air trunk it makes at least 3 more bends. This is why I used 8" duct instead of choking it down to 6". The blower only puts out about 200 CFM, so it's just a little push, it doesnt scream through there.

The Silver Star is a real simple design, just a 10 gauge steel box with a round top and a simple, gravity-sealed door. Theres a plenum built around it with an outlet duct at the top. No grate or ash pan, I added a small fireplace grate and keep about 1" of ash in the bottom of the firebox to insulate it.

 

[whiting-5]

200 cfm thats squat trying to push air through 25 feet of 8 inch duct with bends etc. what size is the hole/duct opening coming out of heater?and what are you doing about gettin the air out of this duct do you have it feeding other lines or is it just coming out the other end unresticted?

 

[AOD]

200 cfm thats squat trying to push air through 25 feet of 8 inch duct with bends etc. what size is the hole/duct opening coming out of heater?and what are you doing about gettin the air out of this duct do you have it feeding other lines or is it just coming out the other end unresticted?

It's a 7" outlet from the wood furnace, which I upped to an 8" once it got under the house. It's tied into the could air plenum of the gas furnace where the hot air just rises by gravity and comes out of the large cold air return at the center of the house. It actually doesn't do too bad of a job heating, it's just very slow to warm up the house. I'd like a blower about twice that size to push it a bit better but in the meantime I gotta work with what I got.

 

[BlueRidgeMark]

The blower only puts out about 200 CFM, so it's just a little push, it doesnt scream through there.

Right there is a big part of your problem. Your duct is too big. You've got your hot air just moseying through the ductwork, taking its sweet time, and losing heat every second.

Speed up the air and insulate that duct!

 

[whiting-5]

yes you must insulate just got done running duct for mine i got mine from hvac store its like r-4 duct wrap . i know on mine i started out with 18" and after 45 feet its down to 12" blows the same at start as finish i dont know about going larger seems like you would lose pressure seems like you would have to drop down in size to maintain pressure and make as straight as possible and the stoves ive looked at must have some kind of back pressure they just cant freewheel just my 2 cents

 

[rsscully]

You could install one of these http://snipurl.com/5b7fb

I used one on my 6" duct that was feeding three of my five upstairs rooms. Really made a difference.

 

[mtfallsmikey]

Slide-on duct wrap is available if you have round Galv. duct, may have to get
it from an HVAC distributor....also, get some duct sealant, apply before the insulation, on all joints.

 

[weloveburning]

I'd up the fan as well. Ours has a 850cfm fan that pushes much faster than the 235 that was on our older furnace. Ours runs 15 ft before it is piped into our plenum on our furnace. But with the 850cfm fan, we can now turn on the LP fan and push HOT air into the back rooms, before, we would only get cold air coming out the vents.

I have to agree that the size of your duct is way to big for the length that you are trying to push it, thus giving you more surface to cool it down before it gets to the furnace. The isulation will help, but also you will get more push with smaller duct. Ours is reduced down to 6" and it pushes plenty of heat to the furnace across the 15ft.

 

[wdchuck]

AOD...

You mentioned crawl space, is the duct touching the ground at all, or is fastened to the joists? Duct touching any ground will lose a lot of thermal energy at that point. Just a suggestion.

Boosting the fan will obviously help, and yes, that 8" is awful big for that little fan. A bathroom fan is stronger.

 

[AOD]

AOD...

You mentioned crawl space, is the duct touching the ground at all, or is fastened to the joists? Duct touching any ground will lose a lot of thermal energy at that point. Just a suggestion.

Boosting the fan will obviously help, and yes, that 8" is awful big for that little fan. A bathroom fan is stronger.

Nah, it's not touching anything other than the pope hangers I have it hung from. I sealed all of the joints with tape and started putting some wrap on it, I will see how it does after I use up the first package of duct wrap, that stuff isn't cheap!

 

[cord arrow]

Each 90 degree bend in an airflow route adds a whopping 20 feet of linear run..

Back in my HVAC days I balanced many systems...mainly by reducing the number of right angles in the long runs...

Many times there would be a 90..on a 90...to, say, turn and lift into a joist space. Well, there's 40 feet right there...all the while running the same diameter pipe. You couldn't get a match flame to wiggle at the end of some of these runs.

Boosters were no help...the air had too much time to cool...need to make your runs as straight as possible...many times it's ugly...but far more efficient.

 

[cord arrow]

John Q. Homeowner didn't care so much about the pipes hanging every which way in his basement after I was able to provide heat to the back bedroom of a large ranch home...

But it sure looked tidy when he bought the place...inefficient, but tidy...