Running forced air return in crawlspace to heat a distant room?

[arnoldez]

We installed a new wood burning insert this year, and this baby puts out some heat! The issue is that our house of course isn't laid out to really benefit in terms of heating the entire house. One room in particular towards the rear doesn't really seem to heat at all, so I'm trying to find a cost-efficient way to move some air between the two rooms.
The house is a 3-bedroom ranch style with a crawlspace and an attic. We also have The ceilings are too low to install transoms above any doors, and the bedroom doors are generally kept closed at night to keep pets out, making air movement difficult with simple fans.
We do have a central HVAC system with a decently located air return in the same room as the fireplace. We tried this solution during some cooler months, and it did seem to help, though I'm not sure it would be enough on the coldest nights. I am also weary of keeping the fan on at all times to distribute air. I suppose a secondary question is whether I should be concerned about wear and tear?
Anyways, my current idea is to install some basic floor registers in the bedroom and the living room (where the fireplace is located) and run a powered fan through ductwork in my crawlspace to push cold air from the bedroom into the living room. Does this make sense? If so, what are some things I need to keep in mind? And does anyone have an idea on what this might cost?
I've attached a rough layout of our house for a visual. It's not to scale, but it should give you some idea of what I'm dealing with. The grey vents in the illustration are air returns. Every room has a supply vent.

 

[stoveliker]

The crawlspace is likely (freezing) cold. Ducts are generally not insulated well enough to not have significant losses from such a set up.
If you would have a thru-the-wall fan between the master and the guest room, and move heat this way into the guest room (assuming heat can get into the master by leaving that door cracked?). If there is an inch under the door to the guest room, the cold air there can move back towards the LR to complete the cycle.

This way you don't waste heat thru ducting outside of the insulated envelope.

 

[bholler]

We installed a new wood burning insert this year, and this baby puts out some heat! The issue is that our house of course isn't laid out to really benefit in terms of heating the entire house. One room in particular towards the rear doesn't really seem to heat at all, so I'm trying to find a cost-efficient way to move some air between the two rooms.
The house is a 3-bedroom ranch style with a crawlspace and an attic. We also have The ceilings are too low to install transoms above any doors, and the bedroom doors are generally kept closed at night to keep pets out, making air movement difficult with simple fans.
We do have a central HVAC system with a decently located air return in the same room as the fireplace. We tried this solution during some cooler months, and it did seem to help, though I'm not sure it would be enough on the coldest nights. I am also weary of keeping the fan on at all times to distribute air. I suppose a secondary question is whether I should be concerned about wear and tear?
Anyways, my current idea is to install some basic floor registers in the bedroom and the living room (where the fireplace is located) and run a powered fan through ductwork in my crawlspace to push cold air from the bedroom into the living room. Does this make sense? If so, what are some things I need to keep in mind? And does anyone have an idea on what this might cost?
I've attached a rough layout of our house for a visual. It's not to scale, but it should give you some idea of what I'm dealing with. The grey vents in the illustration are air returns. Every room has a supply vent.

View attachment 298977

The cold air return needs to be atleast 10' from the stove btw

 

[arnoldez]

The crawlspace is likely (freezing) cold. Ducts are generally not insulated well enough to not have significant losses from such a set up.
If you would have a thru-the-wall fan between the master and the guest room, and move heat this way into the guest room (assuming heat can get into the master by leaving that door cracked?). If there is an inch under the door to the guest room, the cold air there can move back towards the LR to complete the cycle.

This way you don't waste heat thru ducting outside of the insulated envelope.

I had considered wall fans, but those two rooms between the master and guest room are a bathroom and closet. Also, not shown is a closet for the guest room that backs up against the master closet. I would need as many as 3 or 4 fans to complete it, and I'd rather not have air blasting from my bathroom into my master bedroom if I can help it... The closet doesn't really allow for much airflow due to hanging clothes.
I was worried about losing heat below the house, but my thought was that the stove burns so hot, I'd actually welcome the cooler air in the living area. I may waste some heat, but the total amount of heat output is probably more than the house requires anyway – it's just not distributing where it needs to go.
Would it be better to run the duct through the attic? I was initially thinking the floor because I wanted to collect the cool air, but I could be persuaded otherwise if it makes sense.
Thanks for the reply!
Edit to add: Regarding the temperature of the crawl space, our house is located in western North Carolina, so the temperatures don't drop that drastically. Our crawlspace is never freezing, and the temps here rarely go below the 20s (if that). We get maybe 2 or 3 snow days a year. I understand it can still be an issue, but just wanted to make note that this isn't Michigan or something in the cold north.

 

[begreen]

The cold air return needs to be atleast 10' from the stove btw

If I understand the plan correctly, in this case the register in the living room would be the supply register with the return in the bedroom. This could work if the duct is well insulated and protected from rodent damage to the insulation. The guest br door would need to remain open or have a vent grille or be cut up about an inch at the bottom to allow the free flow of air. Also, the duct could have a Y or T that connects a run to the office too with another return grille there.

 

[arnoldez]

The cold air return needs to be atleast 10' from the stove btw

I think it would be, but can I ask why? I hadn't heard that before.
Our plan was to put it in the floor near one of the walls either across from the fireplace or the external wall towards the top of the image, because then it would sit under furniture and not be visible. Both of these measure at least 10 feet away, but the HVAC return also sits directly above one of them – wasn't sure if that would cause an issue.

 

[arnoldez]

If I understand the plan correctly, in this case the register in the living room would be the supply register with the return in the bedroom. This could work if the duct is well insulated and protected from rodent damage to the insulation.

That is correct. The cold air in the guest room would be forced through ducting under the house, towards the warm living room.

 

[begreen]

I think it would be, but can I ask why? I hadn't heard that before.

This is mechanical code. It is to prevent negative pressure near the stove. In this case, not an issue, the return is in the far bedroom.

 

[stoveliker]

But, if the only air that comes into the bedroom is coming from under the door, you'll be getting the coldest air in the home (i.e. the air on the floor) into the bedroom.

I would then put a through register in the wall above the door to the bedroom. Then you get warm air there. (It'll get down because that return register will be low in the bedroom.)

 

[EbS-P]

Two thoughts.

Costs online duct fans go from cheap to expensive thinking 100-200 cfm? 100$ would get something. R6 flex duct 2$ a foot. Boots and grills call it a another 40$.

Have you tried a small fan set on low, on the floor in the office and bedroom blowing down the hallway. Spending the 200+$ on air sealing the bedrooms and adding insulation.

I have a ranch 3 bedrooms at the end of the hallway but the ceiling is flat from stove to end of hall. Ceiling fan in up blowing mode with a fan at the end of hallway on floor blowing to stove helps a lot.

 

[begreen]

But, if the only air that comes into the bedroom is coming from under the door, you'll be getting the coldest air in the home (i.e. the air on the floor) into the bedroom.

I would then put a through register in the wall above the door to the bedroom. Then you get warm air there. (It'll get down because that return register will be low in the bedroom.)

No, it will be warmed air coming from the stove room via the hallway.

 

[stoveliker]

But the floor of the hallway will be the coldest air that is not in the bedroom.

Normally we prefer to send that air towards the stove.

 

[stoveliker]

My point was that it was best to have the air from the hallway enter the room higher up (especially if the return register to the stove is low inthe bedroom).

 

[arnoldez]

Two thoughts.

Costs online duct fans go from cheap to expensive thinking 100-200 cfm? 100$ would get something. R6 flex duct 2$ a foot. Boots and grills call it a another 40$.

Have you tried a small fan set on low, on the floor in the office and bedroom blowing down the hallway. Spending the 200+$ on air sealing the bedrooms and adding insulation.

I have a ranch 3 bedrooms at the end of the hallway but the ceiling is flat from stove to end of hall. Ceiling fan in up blowing mode with a fan at the end of hallway on floor blowing to stove helps a lot.

I've tried a fan, but with the door closed, it's not very effective. I'm trying to find a way to move air with the door closed.

The HVAC fan helps a fair bit, so I believe the heat can make its way to the room that way. I'm just trying to find ways to complete the cycle of moving the cold air out more effectively.

I may try the fan idea with doors open when no one is in there just to track the temperature change. This should in theory give me an idea of what's possible before blowing the $200 on duct work.

 

[arnoldez]

But, if the only air that comes into the bedroom is coming from under the door, you'll be getting the coldest air in the home (i.e. the air on the floor) into the bedroom.

I would then put a through register in the wall above the door to the bedroom. Then you get warm air there. (It'll get down because that return register will be low in the bedroom.)

I had considered the register above the door. It's just really ugly 😩

 

[begreen]

I had considered the register above the door. It's just really ugly 😩

Leave the door open and it's not an issue. The air pulled up the hallway from the stove room will be several degrees warmer than the guest room's, even if pulled under the door.

 

[EbS-P]

Just to revisit this with an added point. Studies(no source here but I believe it) on existing house showed that running the hvac blower with the front doo open increased house leakage rate by 5x. And closing the door increased the leakage rate by almost 10x.

HVAC systems are leaky and only operate on differential pressure. Depressurizing one part of the house near the air return. And pressuring parts near the vents. We should stop thinking about blowers as movers of air but rather pressurizing/ depressurizing appliances. Sure your hvac contractor was supposed to to all the calculations and air balancing to minimize this but I’m guessing it wasn’t done.

I don’t think adding the proposed blower and fan are bad ideas just be aware the impacts of the leaks present in an hvac system.

 

[begreen]

A well-balanced hvac system should be neutral, but there are a lot of poorly designed and balanced systems out there. This is frequently made worse by homeowners either inadvertently or intentionally blocking off supplies and return grilles.

 

[bcrtops]

This will work to a degree, but maybe not as welll as your expectations.

Our house has a similar layout, & we use a similar system, but have RETURN air vents in all 4 rooms, & exhaust/exit into the living room. The temperature in the 4 rooms will get up to within 10 degrees of the Living Room after 1-2 hours. We only turn that fan on when the Living Room gets too hot, however & not as a main method of heating the back rooms. We, also, just use a fan on the floor at the back of the hallway, blowing cold air back towards the Living area. This makes much less noise, & works well until the outside temp goes below freezing. The fan on the floor accomplises the same thing, though takes a bit longer to get any heat to the back rooms.

 

[TahoeJim]

@arnoldez super interested in what you try here, and any results. I have a similar situation where my stove is in the dining room /kitchen on the north side of my house and our living room is on the opposite (south side) of the house, and full of windows. Dining room is hot, living room is cold.
From everything I've read, moving cold air to the stove is the right approach.
You could test this with a run of ducting on the floor from a far cold (guest or office) room to your stove, and a cheap inline fan. Pretty low dollar commitment (ie no cutting, no grills, etc) to see what the effect is. The problem you are going to have is if you keep those doors closed, you aren't going to allow the warm air to get back to those rooms no matter what you do. You either leave doors open, put in a transom vent, or maybe use a split door to keep your pets out.

 

[TahoeJim]

also you could put vents in the doors that you want to keep closed as an option to the transom vent

 

[FPX Dude]

or keep door open and use some kind of "baby gate"