Somewhat disappointed in air distribution

[beelzerob]

Our floorplan is pretty open, which was part of the reason we put a high-efficiency wood burning fireplace in the great room. It does a great job of heating the great room, and pretty much the entire upstairs.

My plan had always been, though, to run the HVAC fan to distribute that heat to other rooms....basically try to even out the temps in all rooms, since the upper rooms were pretty toasty, and the first floor rooms were still kinda cool.

So, I hooked up my temp sensors, loaded the HVAC driver, and off I went!

The results have been disappointing. When the loft was 72, I monitored the temperature probe that's directly above the HVAC fan. 65 deg was about its max. That's not going to warm any rooms! So, I cranked up the temp of the fireplace, and I closed all the vents on the 2nd floor, but opened the cold air returns. I did the opposite on the first floor, thinking that way the hot air would be sucked from the 2nd floor and blown into the first floor. With the temp in the loft then 75, the max temp I saw in the HVAC duct was 68. That MIGHT be warming up some rooms...but not by much.

Does the air really lose that much heat during the journey? I had thought that by pulling and mixing all the air from all the rooms, and with some of it getting spewed back out in the great room near the fireplace, that eventually all the rooms would even out in temperature. That doesn't appear to be the case.

The fireplace still does a great job of warming up most of the house...certainly the 2nd floor rooms, which is good since 3 of the 4 bedrooms are up there...but I guess I should have checked some of my assumptions first.

 

[Macca]

I have to agree with your findings, as they mirror my own experience. Our system has a intake located directly above the fireplace that is opened by a thermostat once the living area reaches a preset temperature. Once open, the pump sucks the warm air accumulated at the ceiling and pumps it around 20m via insulated ducts to the duct outlets int he bedrooms. I have 1-wire temp sensors at the intake, pump and bedroom outlets.

Data from last week shows the following:

Intake Temp 39.5C
Pump Temp 35.3C
Bedroom 1 23.5
Bedroom 2 25.2
Bedroom 3 25.1

If we close the bedroom doors, then over a 1-2 hour period these rooms will be heated really well. But if left open, then the heating is not particularly good. I think its possible that heated air travelling through a duct system loses 1-2 degrees Celsius per meter it travels, although I have no proof of this thory other than my data I have recorded over the past year. I am sure an HVAC expert could shed more light on this....

 

[sic0048]

I'm sure the system looses a lot of heat as the air travels. You have to realize that the heat produced by a furnance is much greater than 75 degrees and it is pumped through the system to all the rooms. When it comes out, it is generally hot, but much less than right off the furnace. To take air that is only 75 degrees to start with, it isn't going to help much in the way of heating other rooms.

You could stick a temp probe in the main duct as it leaves the furnace to get a good base temp and then a couple of probes at registers in the rooms and see how much heat loss there is in the system normally. Then apply this % heat loss to 75 degree heat and see what you come up with.

 

[Lagerhead]

I'm sure the system looses a lot of heat as the air travels.

But-but-but -- but then, where does the heat go? It can't be "lost"!

If you have ever had a heat pump you know that patience is mandatory. A heat pump does not develop high temperatures, like a furnace, but produces only a few degrees of warming above ambient which, in turn, results in very gradual changes in temperature. Or, maybe you have used a muffin fan (remember the "energy crisis" of many years ago?) to move the air from a stove-heated room into another unheated room. It works, but it takes time. Could it be that some of these factors apply to your situation?

 

[applianceman]

Hi Guys,

The rising heat in a home is called a "stack effect". It is extremely hard to overcome that by pulling air from a higher warmer area and trying to push it into a lower cooler area. It can be done, but the volume of air being pulled down would have to be extreme. Even if you were able to accomplish this, the rapid movement of air entering the lower, cooler area would cause occupants to feel cold just because of the air movement.

 

[beelzerob]

Well, I guess as an experiment, I could completely cover all of the cold air returns on the first floor so it can only pull air from the 2nd floor, just to see if that makes a difference in the HVAC internal temp.

Ya, I know the heat pump isn't a fantastic heat source either...well, at least not a big heat source, not like straight fuel. I was warned about that when we got it, and it's true...it feels like cold air coming out of the vent, but it does slowly do the trick. When it was running, I was seeing 90 deg above the fan, so that's pretty good. But that also depends on the outside temp if it can get that high.

I suppose in that theory then, maybe I need to let the fan run longer to circulate the air and then maybe it will start to even out? I think I let it run close to an hour last time I was watching it.

This will be more interesting when it gets really cold.....really so far, there is no part of the house that is significantly cold, except our master bedroom if we close the doors. Then it gets cold. But open the double doors, and it warms right up like the other rooms.

 

[RAM]

Well, I guess as an experiment, I could completely cover all of the cold air returns on the first floor so it can only pull air from the 2nd floor, just to see if that makes a difference in the HVAC internal temp.

I would be careful not to do this when the furnace is trying to run in it's normal mode. If you restrict the amount of air running through the furnace when it is running you can overheat and damage the heat exchanger in the furnace.

 

[beelzerob]

Well, I noticed that at each cold air return, there is a grill with a louvre handle, and one without. So I figure they must have put the non-closeable grill there so you can't accidentally shut off all the air to the system.

so my thought would be...if I still end up with the same number of open cold air returns upstairs as there are non-closeable ones in the entire house, then I should be at least at the min acceptable.

But otherwise, I agree...as it's not the way i'd want the system to run if we actually ran the heat pump. I guess it's just an experiment to see if force feeding it the hotter upstairs air can bring that HVAC temp up to a reasonable value.

 

[CollinR]

Might be interesting to take some vacuum readings before the filter and after the filter.

This will tell you a couple few things. Do you have enough returns open? Do you need to change the filter?


In the future you can vary the returns up\down based on temp and use vacuum load to open additional returns as required..

 

[beelzerob]

Hmm..that's a good point, it's probably time to check the filter.

 

[beelzerob]

Well, I found a way to distribute the heat through the house using the hvac fan...put too much wood on the fire!

I did that last night and opened the airflow all the way up, and by the time I turned it all the way down, it was 78 in the greatroom and the loft up above. :lol: So I turned on the hvac fan, and was getting 72 deg at the fan. Woot! Of course, who knows how much more it dropped down by the time it got to the registers...but I guess that's one way to do it.

I mainly turned on the fan just to blow some colder air into the room we were in. Geez, it was warm.

 

[Xpendable]

Well, I found a way to distribute the heat through the house using the hvac fan...put too much wood on the fire!

I did that last night and opened the airflow all the way up, and by the time I turned it all the way down, it was 78 in the greatroom and the loft up above. :lol: So I turned on the hvac fan, and was getting 72 deg at the fan. Woot! Of course, who knows how much more it dropped down by the time it got to the registers...but I guess that's one way to do it.

I mainly turned on the fan just to blow some colder air into the room we were in. Geez, it was warm.

Be very careful about putting too much wood in your fireplace. You can actually damage the fireplace and even cause your house to burn down. You wouldn't think that could happen, but it does. Fires that are too big for the chimney can cause the chimney to crack. Cracks are very dangerous because they can let extreme heat escape into unseen areas of your home, possibly igniting your house on fire (usually in the upper floors, attics, or roofs).

 

[123]

If you want to improve the efficiency of your fireplace, consider installing a fireplace insert. Basically, its a stove that fits into an existing fireplace opening. The amount of heat it can generate is astounding. The installation requires the installation of a stainless steel chimney liner.

If you like watching flames, the "light show" created by a fireplace insert is impressive. Swirling, roiling, cascades of flame when its running full tilt! I have this one and I'm very pleased with it. The squirrel-cage blower fan helps to distribute the hot air.

The double-wall steel construction makes for a safer combustion device compared to an open fireplace. The combustion chamber is designed to improve overall efficiency. If you like an occasional "open fire", the door is easily removed and replaced with a wire-mesh door (stops flying embers).

Guests usually say: Wow! I can't believe how much heat it puts out!

 

[maknoll]

If you want to improve the efficiency of your fireplace, consider installing a fireplace insert.

What he's describing sounds just like an insert to me (or at least a decent wood burner).

We heat two floors of our home with a fireplace insert. It has been our experience, as others have posted, that it takes a while (several hours) to even things out. Do run your HVAC fan. If I start a fire say around 4 or 5PM, it's still pretty cool in the upstairs bedrooms at bedtime. Burning all weekend, however, things even out quite nicely. Still a difference, of course, but not terrible.

 

[beelzerob]

We have a Quadra-Fire 7100. It heats very hot. As I said, the entire 2nd floor of our house is definitely comfy. It's just the first floor that's not as warm as I'd like.

I was just getting to the point of thinking of leaving the fan on almost all day, to see what it comes out as. Sure, it may be losing heat initially when it goes through, but eventually it would heat up the duct enough so the loss is minimized.

The other thing I'm doing is calibrating my temp sensors, as some of them it turns out are pretty off. I'm also going to do more to plug the cold air returns on the first floor, so only the warmer air from upstairs gets taken.

We'll see if that helps the situation.