Mechanical Room
We are almost finished building a detached 3 car garage with a 2 bedroom apartment above. Both the garage and the apartment will have heat and AC supplied by a Heat Pump.
We built a Mechanical Room underneath the stairs in the garage and separated it from the garage with an insulated wall and interior door. This room is about 4×20 with a severe sloped ceiling (stairs). It houses the 200 Amp Service, the HVAC Air handler and line sets and a 50 gallon HP Water Heater.
The water heater will be exhausting cool dry air as it works. Should I be concerned it will not have enough air circulation or it will not provide the dehumidified air to the garage when I have the door closed? Should I leave this door open? Should I put a passive vent in the mechanical room wall?
Or am I overthinking this?
As I mentioned the garage will be conditioned but the dryer air the better in there for my cars. We live on the water.
Thanks
Nick
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Standard practice commerically is to put a louvered vent in the door, usually down low, sometimes two vents, one low and the other high on the door. Best for airflow through the room would be a crossflow setup though, with one vent at either end of the space, the intake down low, and the exhaust up high.
BTW, 4 feet is really too narrow for a mechanical room. You are just barely making the code required clearance for electrical panels, and there isn't going to be enough room to maintain the other equipment, especially if something needs to be replaced. I know you've already built the place, so you're probably stuck, but you normally want mechanical rooms to be AT LEAST 6 feet in the smallest dimension, and ideally a bit more. There should be enough room for the largest piece of equipment plus a MINIMUM three foot isle on at least one side for maintenance work. Four foot access isles are much better, and should really be on at least two sides of the equipment. At work, I design with 6 foot clearnance for service, but those facilities are different (critical facilities that have to be maintained while running).
It's very important to always allow room for future maintenance/service work, and resist the temptation to try to squeeze the mechanicals into the absolute smallest space possible.
Bill
You can duct the exhaust air from the HPWH out of the room using 8" flexible duct. If you have a louvered door that should give good air flow. The duct adaptor for the water heater can be hard to find, I ended up just cobbling something together out of 3/4" plywood.
Which brand is your HPWH? There is no reason to guess here, read the installation manual. On Rheem’s manual it is page 6 that clearly states the airflow requirements and when louvered doors are required.
Thank you all. The HPWH isn't installed quite yet, but I guarantee you it won't be a Rheem.
I think the simplest solution is to just leave the door to the mechanical room open. If that doesn't suffice, I'll put in some wall vents.
If you just plan to leave the door open, someone will inevitably close it at some point. Vents are a better long-term option. If you do go with the "leave it open" method, I'd recommend putting a hook and eye latch on the wall to hold the door open. That will at least discourage someone from trying to close the door at some point in the future.
Bill
If I was going to leave a door open all the time, I'd take the door off the hinges.
Possible. Let's see how it goes. Hopefully we'll be in the building by 11/1.
I can tell you this: this morning the garage was warmer than my house and there's no heat in that building. Modern insulation and air sealing provide a dramatic difference in comfort.
Having just looked up the required space for an AO Smith 50 gallon HPWH myself, I can tell you the minimum space you need is 450 cubic feet. Your 4' x 20' mechanical room with a sloped ceiling may or may not be 450 cubic feet.
If the room is not 450 cubic feet, you need a fully louvered door ($~200 at Big Box store) or 130 square inches of grille vent space, split between a low vent and high vent (a big door undercut can substitute for the low vent).
If secondarily, you want the cool, dry exhaust air well mixed in your garage, you might want no door at all, or a fully louvered door.
Propping the door open will definitely do the trick... until someone other than you closes it and you get mad at them!