0 Helpful?

Furnace / hot water heater closet location and size

I am at climate zone 3.

I initially planned to put furnace and hot water heater in the attic. Since it is more energy efficient to put furnace in the conditioned space, I found a couple corners (bedroom closet and bathroom corner)


1. Can a furnace fit into 2' deep closet?
2. What's the minimal size required for the furnace closet and access limitation?
3. Is there any issue placing a furnace in a bedroom closet?

For hot water heater, is it also more energy efficient to place it in the conditioned space? If not, I probably will leave it in the attic (my garage is too small - 20 * 18).

Thank you!

Asked by Rian Bart
Posted Feb 26, 2011 3:07 AM ET


4 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Q. "Can a furnace fit into 2' deep closet?"

A. No. I'm not saying it's technically impossible -- someone has probably done it, because you see such things in mobile homes -- but you don't want to do it. You need plenty of room to facilitate installation, and you need room for maintenance personnel to get in there. Moreover, you have to imagine duct layouts -- how will you run the main supply duct leaving the supply plenum? How will you route the return ducts to the return plenum?

Q. "What's the minimal size required for the furnace closet and access limitation?"

A. Most mechanical rooms are way too small. I think such a room should be at least 6' x 8' -- bigger is better -- but my sympathies always lie with the service personnel, not the homeowner who is giving up living space. Duct layouts determine mechanical room location.

Q. "Is there any issue placing a furnace in a bedroom closet?"

A. Yes. Furnaces are noisy.

Answered by Martin Holladay
Posted Feb 26, 2011 7:01 AM ET
Edited Feb 26, 2011 7:03 AM ET.


You cannot install a furnace in a bedroom closet. Most of my home designs have dedicated hallway closets for furnaces and WHs (unless I’m using tankless) to place the WH within 30’ of the furthest faucet and minimal duct runs. The size of the closet depends on the furnace, but in most cases you can install a furnace and a WH in a 36” deep x 60” wide closet. Of course, its better if you have more room, like Martin said. You can install double 24” doors for access and maintenance and the equipment must be seal combustion.
If you want to install just the furnace, a 36”x36” hallway closet can be fine for a small furnace. Also, consult with your HVAC contractor for equipment specifications.

Answered by Armando Cobo
Posted Feb 26, 2011 10:16 AM ET


We routinely install heat pump air handlers in 30" deep insulated interior closets, generally with 6'8 tall 8'0 wide insulated doors that open wide to allow access to the HVAC, demand water heaters and solar hot water equipment. As Martin points out the noise is an issue so we line the closets with OSB or Thermo-ply and insulate the back of that with foam or fiberglass before drywall. The doors get foam on the back and have bump-up seal on the floor as well as top and sides and center. Even so the noise is still an issue for light sleepers. Consulting with the HVAC contractor and others involves (electrician, plumber) is critical, it's not just the HVAC cabinet. The condensate drain, duct work, access to zone dampers and balancing dampers and general supply and return air duct design all need to be accommodated in the HVAC space design. We got it wrong on one house in particular by six inches and there was really nothing to be done but re-frame the wall. Inches count here. Big doors rule.

The drawing below shows a 22x22 counter flow air handler cab on a zoned bypass duct system with a demand water heater and a 120 gallon drain-back solar all packed into a 28" x 10'4" closet. The project manager, plumber, solar, HVAC, and electrical folks all had to work together very smoothly to make this work well.

Mechanical detail.jpg
Answered by Michael Chandler
Posted Feb 26, 2011 1:02 PM ET


"Is there any issue placing a furnace in a bedroom closet?"

You also need to be concerned with proper combustion air and make up air. Even some sealed combustion appliances have minimum combustion air requirements.
Our mechanical code also requires that the door has an automatic closer installed if in a bedroom closet.

Answered by Danny Kelly
Posted Feb 26, 2011 10:51 PM ET

Other Questions in Energy efficiency and durability

Mortar bridging and droppings

In General questions | Asked by Stephen Cook | Jun 16, 18

Building Code Reqs for Stacked Window Headers, Bracing, Stucco over Foam

In Building Code Questions | Asked by Zane Bridgers | Jun 17, 18

Roof / wall connection showing vent above structural sheathing

In Green building techniques | Asked by Ethan T | Jun 15, 18

Room over garage

In General questions | Asked by Jay Raja | Jun 16, 18

Do I need an HRV/ERV for a house built in 1947?

In Mechanicals | Asked by Will82 | Jun 14, 18
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!