I have a 30x50 shop with high ceilings. It has a fireplace but I can only get about a 5-7 temp rise no matter how strong the fire is going. The fireplace is an old insert (circa late 1980's) with a fan, but just doesn't put out near enough heat. I've also placed a large fan in front of the fireplace to help move air around, still woefully insufficient. I've read that a lot of fireplaces are only about 10% efficient, whereas a wood stove is more like 75%. The shop is lightly insulated (ceiling is drywall with insulation, walls are reflective bubble wrap stuff) and while I know it would help, it would be a major operation to properly insulate it. I am considering a wood or pellet stove and tying into the existing chimney (I am pretty sure it needs to be a proper wood stove double wall pipe). Just looking for opinions or advice on the matter. Thanks.
Convert fireplace to woodstove or similar
- Thread starter ChiknNutz
- Start date
Try making sure the combustion chamber of the insert has an outside air source. You are likely pulling combustion air out of the environmental space. If it's a typical insert, it should have the proper chimney setup in it, unless you're talking about a steel insert in an existing brick fire box, in which case it should have clay flue liners out the roof. Still need outside combustion air.
I'd check to see what temps were at ceiling height. You might just need a fan or two to move air back down into the work area. And, we had an 80's insert in our house that seemed pretty efficient--I think open fireplaces are least efficient.
ChiknNutz:
It’s probably asking a lot for a fireplace to heat 1500 square feet of space with a high ceiling. I’m not sure what reflective bubble wrap is exactly, but if there is no fireblocking in your studs, it would be rather easy to drill a hole and blow in insulation into the stud cavities, and if there is fireblocking, blow it in through a hole below the fireblocking into each stud cavity as well. You could also blow additional insulation onto your ceiling, and this might help a lot towards keeping your space warm once it gets warm.
If you have additional amperage in your panel box, you might consider additional wiring and placing some electrical heaters around the perimeter of the space, with some ceiling fans to help keep the heat off of the ceiling. No outside ventilation required, and less of a chance of fire if you keep anything combustible a proper distance from the front of the heaters, and blow them off once in a blue moon.
A wood stove in a fireplace cavity will need to have a good, clean, double wall steel or ceramic lined masonry chimney. You can dial in a woodstove and flue damper so that the fire burns a long time, or to produce a lot of heat fairly quickly, but if by high ceiling you mean over ten feet tall, then you are heating at least 15,000 cubic feet of space. While some fireplace inserts and stoves can crank out some serious BTU’s, heating the space from one central source at one end is going to produce hot and cold spots, especially at the extremities away from the fire, whereas electric heaters placed around the perimeter will provide a more even heating and be more controllable.
FWIW. YMMV. Good luck.
Tone
It’s probably asking a lot for a fireplace to heat 1500 square feet of space with a high ceiling. I’m not sure what reflective bubble wrap is exactly, but if there is no fireblocking in your studs, it would be rather easy to drill a hole and blow in insulation into the stud cavities, and if there is fireblocking, blow it in through a hole below the fireblocking into each stud cavity as well. You could also blow additional insulation onto your ceiling, and this might help a lot towards keeping your space warm once it gets warm.
If you have additional amperage in your panel box, you might consider additional wiring and placing some electrical heaters around the perimeter of the space, with some ceiling fans to help keep the heat off of the ceiling. No outside ventilation required, and less of a chance of fire if you keep anything combustible a proper distance from the front of the heaters, and blow them off once in a blue moon.
A wood stove in a fireplace cavity will need to have a good, clean, double wall steel or ceramic lined masonry chimney. You can dial in a woodstove and flue damper so that the fire burns a long time, or to produce a lot of heat fairly quickly, but if by high ceiling you mean over ten feet tall, then you are heating at least 15,000 cubic feet of space. While some fireplace inserts and stoves can crank out some serious BTU’s, heating the space from one central source at one end is going to produce hot and cold spots, especially at the extremities away from the fire, whereas electric heaters placed around the perimeter will provide a more even heating and be more controllable.
FWIW. YMMV. Good luck.
Tone
Thanks for the replies. The building has no internal studs. It is essentially a pole building with metal siding. On the inside the PO applied the reflective bubble-wrap material. The ceiling is close to 14'. I have one ceiling fan with provisions for three more to help move air around. I do realize it is going to be difficult to heat this space. I am not looking for equivalent to a proper home, just looking for better than what I have now. One thing I've not done that I know would help out a lot is to insulate the roll up doors, likely with rigid pink foam.
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Is the current fireplace open or closed? I have had what they call ventless fireplaces which are enclosed with glass front and vent pipe to the outside. These type are not very good for generating heat, mostly for looks. Even if you add fans as you describe, it wasn't very good. I also had and open type, with no vent. It generated about 200% more heat than the enclosed type. It heated so well that you could turn it way down after the space got warm. The only downfall to the open type are the fumes. They are supposed to be safe, but I found myself getting a headach if exposed to it for extended periods of time. Perhaps that explains why I can't remember sh#tuff anymore. ; )
Back in Texas I had a old drafty vacation cabin and had a
it heated the whole place up.
Fireplace Heater for Masonry Fireplace With Blower
it heated the whole place up.
I had one of these without the manifold and blower, and it could overheat a large great room/kitchen/breakfast nook. The wood burns so cleanly and hot I had to replace the 3 center pipes after 3 seasons. The angle of the top outflows was just right for my space. You could adjust it with spacers under the legs. Also, get a chimney sweep to confirm your existing fireplace is drafting as it should.
I'm not an engineer; my guess is this and a ceiling fans running in reverse will go a long way towards heating your shop. In addition do a thorough job of filling all leaks in the building and insulating the metal doors. No HVAC method can overcome a fundamentally leaky, drafty building.
Put all this together and hopefully you get the big picture. Solving your problem won't get done with one single solution. It will take multiple changes and equipment to evenly and efficiently heat 15,000 cf in a pole building that was never intended to be heated to human occupancy levels.
Any insert without outside air supply and no heat exchanger to circulate heated air back to room is woefully inefficient and may be counter productive drawing in cold drafts through every crack and crevice to provide combustion air that simply drafts out the chimney. Add a high ceiling in a large area and you got quite a challenge. One positive may be that there is a suitable chimney for a good wood or pellet stove. When we moved to VT, the house had several restored brick fireplaces. Look nice but poor heaters. We had a Vermont castings stove from previous house, so we installed the woodstove in the living room fireplace. Basically the pipe off the top of the stove fit through the damper into the chimney liner and the rest of the damper opening was fitted with insulation. It worked very well. Stoves still create some infiltration of outside air but at a lower rate. By throttling the inlet air, I could get it to burn low and slow overnight. It also helps that 300 lbs of cast iron and firebrick retain and then release heat for a long period. It’s been a long time and I really have not kept up with current wood stove tech. Surely by now, they’ve squeezed out as much efficiency as possible for stoves and inserts. I think pellet stoves are the more efficient. I believe some have through the wall vents that bring in outside air while venting the firebox. However in your case, air circulation may be the biggest issue.
The heat pump for the first floor of my home is too small. It works OK for AC but will not heat this part of the house when the temperature goes below freezing. It will maintain low 60s but not the 68 setting of the thermostat. My solution prior to changing it is to use a propane burning fireplace insert. It is not doing all the work but in combination I can keep it at 68 or higher. The insert has it's own double wall chimney inserted inside the masonary fireplace chimney. It also has an outside air intake. It is rated to be 70+% efficient. But my house is insulated and the fireplace insert is not doing all the work. To know what it would take to get your shop up to temperature you need somebody with a program to calculate how many btus it will take. Maybe there is something you could find on line. Once you know how many btus it will take you can see if that is reasonably feasible. I understand it will be a major effort but my guess is insulation may be a lot more cost effective than putting in a heater sufficient to get the shop up to a comfortable temperature. With sufficient insulation your existing unit may be reasonably effective. But you can play with assumptions in the programs HVAC techs use to see the effect of insulation too.
FWIW, there are a slew of online calculators, but I found too much variation to trust any single calc. As a chem eng’r, heat exchange was a routine operation and I have my own spreadsheets for heat exchangers and hvac. I recently went through some estimations for my garage space which is a small 220 sq ft x 9’ ceiling space with 2 uninsulated exterior walls, uninsulated overhead door with some leakage all around perimeter and consumes most of the wall, thankfully an insulated ceiling, and one inside wall with a large 4x8 ft opening to main garage. Online calcs were actually quite varied from 5k - 40k btu some as high as 90k, which is completely absurd. So it’s hard to really trust since the backend assumptions are unknown. Running my own heat loss calcs comes up with 9,260 btu/hr. Of the sites I tried pickhvac was the closest at 10,500. Engineeringtoolbox.com has detail calculations and explanations.
Too much to get into here. But try chatGPT, just clearly define the parameters. Start basic then addon - sort of like: calc btu/hr to heat room from 35 to 65 deg F, xxx sq ft of space with x ft ceiling, xx ft of wall is uninsulated facing outside, xx ft of wall is interior next to unheated room, ceiling has R-xx insulation. Then what if there is y sq ft garage door on one wall with a .5” air gap all around. Then add passage doors. For my garage shop it came out pretty much what I figured.
