Hi all,
I have a carrier gas furnace in the house and it does a great job, except in one room.

We have a mudroom between the living room and garage. It has a few stairs, is on slab, and then the garage. There's a door isolating the living room and it's a good thing because that room stays pretty cold.

Today it is 50F in there, outside is 30F and inside is 70F, so it's an average of the spaces. Ceiling is 14' high at its highest and it has one register (4x12, I think) about half way up the wall. No return in the space. Dampers to that zone are full open (manual operation). 150 ft2 of floor, about 1000 ft3 of volume with the high/sloped ceiling.

I have a flow/temp meter and air is about 105F coming out of the resister at 100ft/min at full blast (3 speed air handler, most of the time in low).

Options for getting more heat in there? Would a dedicated return help?

Or am I stuck with a wall heater / baseboard heater?

Thanks,
Anthony

 

Does this grill have a dedicated duct that runs to the furnace or is this a multistory house with larger ducts that branch out somewhere in the walls?

 

There are two main trunk lines (main floor and upper floor) and a third mini-line off the furnace. This mini line feeds four registers (two on the main floor, one upstairs, and this mudroom one).

All three lines have dampers, but if I fiddle with closing any of them, I get an occasional limit switch cutoff from lack of airflow. All open and I have no problems. System was sized for an eventual basement remodel (years off still), so that's probably why it needs the extra airflow.

 

An inline booster fan might be something to consider.

They install inside of the ductwork.

 

You really need the return you mentioned. With no return that warm air is finding a way out through the shell. Since you have a measurable flow coming in, that tells me you have a lot of leaks to let the air out. When the furnace is not running those leaks are quickly cooling that space off.

Air leakage and insulation are major contributors to a cold room. Tell us about your insulation, windows, doors, and look for obvious air leaks.

Bud

 

Double pane windows with storm, 2x4 walls with bat insulation. Wood and glass door to the mudroom, steel fire door to the garage (only way in/out).

My measurement was with the door open, I will repeat today with the door closed and document the change.

I can knock out a 4" port in cinder block and have a pretty short run to the furnace. It would put the return 4' below the supply, but I can do that wihtout tearing up any walls.

I'll post later today with the results.

Thanks for the help all.

 

@ arc2v, "105F coming out of the resister at 100ft/min at full blast" that represents a known amount of heat entering that room. That numbers with door closed and with a return will be different and is the number you want. Then, you can do a heat loss calculation for just that room and see if you are getting enough.

In addition to the numbers you stated we would need to estimate the insulation level in the vaulted ceiling and know if there is any rigid insulation under that slab. When I have used an Infrared camera to inspect living space built on a slab on grade the results have been poor. A slab inside a frost wall does better but both need insulation around the perimeter and/or under the slab. The exposed edge of a slab creates a cold signature 3' to 4' into a room. If there is no slab insulation, an in ground perimeter layer can be installed when mother nature allows.

Vaulted ceilings are typically under insulated AND the often need to provide ventilation air flow that reduces their performance. Does that room have soffit and ridge venting? Is the vault created by the bottom of the rafters or by using a scissor truss which provides more space for insulation?

I realize your question was about the heat getting out there, but the heat loss side can also provide an improvement.

Also, before I hit send, if you can provide a larger return path than 4" it would be better. If the door closed number is a lot different, play with the door opening, 1/2" as such to get an idea about return size.

Bud

 

I think this is a key as well as the vaulted ceiling. Cold air sinks, so it will hover near the bottom of the stairs. Hot air rises so that it will float toward the ceiling. Your comfort zone, in the middle will be in the mix area and will always feel off. You need a cold air return, but it needs to be set low in the room not high. Possibly tap in under the steps to pull some of that air away. When you have the door closed, it is like blowing into a soda bottle, nothing really gets in. Short term, leave the door open or cracked, long term, get a return vent in there.

 

Not seeing your design of the house, we can't actually offer other advice, but is there an option of lowering the ceiling in the mudroom without affecting the aesthetics of the rest of the house? Keeping that warm air closer to you will make a huge difference. Pictures would help, too. http://www.doityourself.com/forum/el...your-post.html

 

thanks guys.

With the door closed (it has a draft sweep on it), the flow rate is cut in half from open. I removed the sweep and the gap is about the same a 4" pipe for a return. I'll live with the draft for a few days and see if we get more out of the room. If it does work, I can cut a return in better hidden when we remodel that room later this year.

I doubt there's insulation under the slab, just in the walls. Based on what I saw around the can lights a while back, the rafters are not vented in that room, just bat insulation everywhere.

thanks again, I'll report back how a couple of days of return air work in that space.

 

Unvented rafter bays, especially with recessed lights is a real potential problem. Warm air and moisture getting up there with no escape will do some serious damage. Look for siffit and ridge venting, on a newer home they must be there.

Bud

 

Most of the house has soffit and ridge venting, but this mudroom is like a 45 degree wedge shape connecting the house and garage. It's the only place with a vaulted ceiling in the house.

There are recessed lights up there, but I can see that bay from the garage and it is well insulated above the lights.

I've been doing some heat loss calculations and wanted to sanity check.

Air Heating Systems

L = Q / (1.08 (th - tr))

Solving for Q (BTU/hr):
Q = L*(1.08 x dT)
dT = 55F

L --> 50 ft/min (measured, low fan speed on furnace) on a 4x10 register. I figured 2/3 average velocity and accounting for the blockage from fins.
L=9.25 cubic feet per minute

This works out to 160W of heat loss. For some reason that sounds low, or maybe that's just because the room is under-supplied.

I'm rusty on all this -- most of my work is mechanical and electrical, not heat loss.

 

I agree that you need a return in the room. What size is the duct going to this room?

 

I would check the temp at ceiling height. If it is warm up there, then I would consider a paddle fan to push the warm air back down.

 

If I let it return through the door gap, it's about a 4" duct in terms of area.

Ceiling is about 3 to 4 F warmer. Not huge.

Right now, I'm fighting the large temp delta to initially heat the room. I may borrow a space heater from work and see if I can get it into the 60's and see how it settles out with the door gap. It's already warmed up about 1 to 2F but that may just be outside temp or solar load on the roof.

Thanks, lots of good ideas.

 

You are not just bringing the air up to temperature, but also everything in the room including floor, stairs and furniture. So give it a good amount of time before your next measurements.

 

Playing with your calculations and not sure what you have. If you are measuring a flow speed of 50 ft/min and the duct register size is 4x10, I get 12.5 CFM. What am I missing?

Bud

 

I "down-rated" the flow to account for the grill blocking some of the overall flow area, and that the flow on the sides is slower than the flow in the center, where I measured.

I went with my gut which was to use 2/3 of the velocity number to factor it all in.

Anthony

 

Well after a month of giving it a return air path, it's still horrible. Very cold in there.

We have an IR camera at work and I took some pictures of the room. Several ceiling corners are just leaking heat and every seam on the outside walls as well. The wall itself outside and to the garage are okay, but the ceiling is just short of being an open vent.

So boosting is probably not enough. A supplemental heater would just be throwing money out the ceiling again. I'll have to focus on insulation first.

Maybe foam insulation and then a wood ceiling on top of it. We need more light anyway, so that would be the easiest way to run it. I'd like to avoid dropping the drywall if I can help it.

Time do do some research.

Thanks for the help all.
Anthony