Gravity kits vs just venting top/bottom of an insulated chase?

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New Member
Aug 8, 2023
Acton, MA
I'm doing new construction and evaluating high-efficiency fireplaces. Spouse won't sign off on freestanding stove. I have fully insulated chase where exterior walls of the chase are insulated to the same specs as the exterior walls of the rest of the home. The home is ~4500sqft split between first and second floor with very open floorplan first floor, 9 ft first floor and 8ft second floor ceilings. The fireplace will be supplemental to multi-zone, ducted heat pump I can use to turnover the air. I don't plan on tying the fireplace to any heat distribution beyond they query here which is gravity kit to the same room for purposes of increased convection.

The question:
I really hate blower noise so looking at models with gravity kits hoping they will aid in convection, but there is very little information on gravity kits to the same room for the purposes of convection. There is also little information on operating without a blower (or without a blower and only gravity kits). Further, with an insulated chase, you can add chase venting near the floor and ceiling that will aid in convection...... but I'm not sure if this is better, worse, or could maybe even be done simultaneously with a gravity kit. Most fireplaces supporting gravity kits support two vents off the fireplace top that can be vented to the same room off the chase near the ceiling. I would probably vent them to the left/right "sides" of a hearth that pushes into the room so they are not visible head-on.

Some models seem to indicate the intake air for the gravity vents is from the chase itself and either venting of chase is required near the floor or an additional gravity intake is required near the floor. Other models imply the intake air for the gravity is just from the front louvers.

Who actually has gravity kits in use and on what models? How do they work for you? Do you use them with or without the stove blower and do they really aid in convection or not?

Fireplaces and the obligatory "request for reccomendation"

If it matters, my short-list of fireplaces includes:
  • PacificEnergy FP30-arch: Established history and knowledge base. Not sure if no-cat is a plus or not.
  • Astria Montecito Estate aka Superior WCT6940: New construction doesn't qualify for the tax credit.
  • Osburn Stratford II aka Valcourt FP10: not sure...
  • RSF Opal 2/3: My wife hates the look in marketing/brochures, the spec looks decent
  • FPX44 or Napolean NZ6000: Seem dated by comparison. Both support a positive pressure type system that seemed to never take off and I don't see it on newer models either; does that mean it had problems? Aircooled stacks.....cheaper and I have insulated chase that should theoretically combat their weakness of poor draw in cold this a pro I should be leveraging or still a con?
  • Supreme Astra 38: A bit smaller than others on the list, but their product manual is the best by far in my opinion. Not sure if that translates to a better stove or not.
  • And probably every other one in this class.....I've been reading manuals for weeks.
Lots of viewing but no feedback or takers yet <grin>.

In my experience so far, the stove shops around me (MA) don't seem to have much insight and most suppliers don't make direct-contact easy. PacificEnergy seems to be an exception with a technical query submission on their home page which I used and, assuming I get a useful answer, I'll post here.

But I'm hopeful others may have real-world experience with their gravity kits (what a bad name....convection kit probably would have been better? I don't really see why "gravity" is very descriptive here, but I guess I'm an engineer and not marketing)
The house is very large. It will need convective fan assistance to see the best performance from the fireplace. The blowers on low speed are pretty quiet. Some have the option of installing a remote blower to further isolate and hide the sound.
"Some have the option of installing a remote blower to further isolate and hide the sound"

The only models I have seen officially supporting external blower are the units that promote establishing a positive pressure (bringing in external air for convective heating with a blower to the firplace). More specifically, the FPX Elite 44 and the Napolean NZ6000. Both of these seem to be older models that also have air-cooled stacks. Even dealers for these two suppliers I have contacted have suggested against them in favor of newer models with class-A stacks and greater efficiency (Napolean dealer pushed NZ3000 Eco vs NZ6000, as example). I'm not sure if this means there were any problems with the approach or not; anyone have recent installs of a model with an external blower?

Thanks for the opinion. Keep them coming!
The Stratford II is probably undersized for that much space and the blower is pretty noisy on high. One of the the biggest challenges of wood heating is getting the air to move.

In our new construction cabin the Stratford II on an interior wall heats the great room/kitchen and loft well, but it takes quite a while to get the warm air back to the bedrooms. Around 1700sf total.
Gravity kits vs just venting top/bottom of an insulated chase?
Nice Stratford II install! I saw some videos on the YouTube of another StratII and yes, the fan seemed pretty noisy.

I'm not too worried about heating entire house in my setup as I'll have zoned heat pumps for far rooms. I will likely be more a weekend burner, so I'm more interested in low noise and convection in the more immediate room. Probably a lean towards "ambiance" without the inefficiency of a "decorative non-EPA fireplace". I don't need the most efficient operation of all time.

One reason for this whole thread: it's not at all clear if, without a blower, circulating the air in an insulated chase or using gravity kits would be reasonable. Again, the chase is entirely insulated. In fact, it's in at in inside corner between two rectangles of the larger house foundation, so only two of the 4 chase walls are actually even external. In such a setup, I'm not sure if gravity vents many larger fireplaces have as options are even useful; I can vent the insulated chase top/bottom or even add some convection assistance fans to the chase venting. Any heating of the chase is essentially heating the house, but this doesn't matter if heat loss from not running a blower goes up an insulated flue vs radiating into the chase.

There may just not be an answer and I'll have to do an install and test in practice. I think I'm going to frame in chase-access from an adjacent closet so I can easily monitor chase temps and install powered convection fans to the chase after the fact. If I do all this, I'll take pictures and post back.
The Stratford II is probably undersized for that much space and the blower is pretty noisy on high. One of the the biggest challenges of wood heating is getting the air to move.

In our new construction cabin the Stratford II on an interior wall heats the great room/kitchen and loft well, but it takes quite a while to get the warm air back to the bedrooms. Around 1700sf total.
View attachment 314382
Usually, it's not necessary to run the fan on high unless trying to raise the temp by several degrees. How is the fan noise on low?
Come to think of it, with chase access post-construction I can even install gravity kits after the fact. Hmmmmm.
It's great If a service access door can be built into the chase. BTW, remember that the chase needs a fireblock at the first floor level.
Fan on low is audible but not distracting.

@Cbell, make sure you check code for the chase walls and the inspectors interpretation. "Airtight" wall surround can be interpreted a couple of ways if that is what code dictates...
I have had a Vermont Castings Winterwarm Large ZC Fireplace (inherited when I bought my current house). And now have installed a Hearthstone Montgomery ZC Fireplace (WFP 75) in its place.

The VC, when ripped out, was noticed to have no gravity kit installed, just vented. And that worked, as far as pumping heat out of the vents. So when I decided to renovate the fireplace last winter, I said, "hell, let's do the gravity kit this time and I'll really maximize the heat coming out of those vents".

Well... I notice little, if any, difference. It could be that the VC was more of a heater than my current fireplace, however. But I would think the blower would be necessary, regardless, in any ZC FP unit.
I got an official response from Pacific Energy so posting it here/below. I'm ~90% sure at this point I'll go with an FP30 Arch if for no other reason that they are the only supplier that gave me a way to reach out to them and ask this question. Plus this seems to be a very well-regarded supplier and model with quite a bit of knowledge on this site.

I plan to vent the chase with access to it to monitor temps and maybe even install some very quiet convection boosting if really necessary. In any case, If this project goes forward, I'll create a new thread of the installation and post a link to it from here.

Hello Colin,

All our stoves are safe to operate without the blowers this would not void the warranty. Not having the blowers on won’t change the amount of heat produced, they just help to make better use of the heat by moving it into the area in front of the fireplace.

Our current FP30LE uses our Remote heat kits that move air using blower, manual is attached. Only the FP30 series A used the gravity kits, we discontinued series A about 10 years ago. Venting the chase is a good option.

With kind regards,
Pacific Energy Online Support
Good choice. Having just come to this thread I wanted to riff on something you originally posted. Seems like you wanted a woodstove and that was thwarted. Well the good thing about the FP30 (and all the FP series, IMO) is that they are built off of woodstove fireboxes. So that FP30 is effectively the same functioning system as a Summit or Alderlea T6 model. They do also have the remote heat/blower option.

Best of luck to you for the whole project.
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My project got delayed a bit with town permitting (the whole home, not the stove/fireplace itself). I'm hoping this is resolved in 2023 and breaking ground in spring 2024. Translation: you might beat me to installation. We'll see!