I am looking for info an make-up air systems to provide ventilation in a home without a HVAC duct heating system. I will be installing a centralized bathroom exhaust fan system and a rather robust kitchen vent hood in a open floor plan ranch style home. I am a little confused to makeup air solutions and the new emphasis on providing such a mechanism in new “tight” construction. Is there a simple solution to provide tempered air w/o existing ductwork in a cathedral ceiling/ICF basement type home?
Thanks!
Replies
Haystax,
No.
Tempered makeup air systems exist, but the equipment is expensive and the energy-penalty (huge electric resistance coils) is very high in winter. Moreover, no such residential equipment exists for large (e.g. 800 cfm) range hoods.
The fault lies at the feet of the manufacturers of large range hoods. These manufacturers are pushing equipment that is difficult to operate in today's tight homes.
Looks like you'll have to get used to opening and closing a window near the kitchen.
Here (in Minneapolis) anything over 300 CFM requires makeup air. Don't know how many other municipalities enforce this, but HVAC inspector approved installation of a hood over 300 CFM without makeup by disabling the highest setting on the last kitchen I did.
Haystax,
Shelter Supply ( http://www.sheltersupply.com ) sells a $1,726 makeup air appliance with a maximum rating of 665 cfm. Above 665 cfm, you're out of luck, unless you install commercial equipment. By the way, that baby draws 10,000 watts when the heating coils come on.
Tempered air? Easy?
No.
Easiest solution is to open a nearby window. Sorry.
Almost any other solution will require ductwork.
You will not get tempered makeup air without a gas or electric make up air unit, found in commercial kitchen installations. Either option will be huge $$$.
Broan makes a line of commercial ERV units in the 1200 cfm range, and they have three speeds. It will require ductwork and maintenance. The units are large. At moderate flow and temperature, some tempering is possible, and electric duct heaters are an option. It will need an electrical connection to the blower motor on your hood as a control device.
One solution for the hood is to get a commercial style model with provisions for ducted makeup air. Because the makeup air is ducted right to the hood, tempering may not be needed.
One solution for the fan is a Skuttle barometric relief damper. It will open only under negative pressure when makeup air is needed. You will get untempered makeup air. Duct it to the space needed, or leave it in the basement.
Another solution for the fan is a residential size ERV ventilator. This will provide tempered air a little easier due to lower flow rates. The "fresh air out" side can be ducted right to the bathroom. Some type of additional control will be needed to turn on the device.
Best of luck.
Edited 2/15/2008 1:12 pm ET by danski0224
Thanks for your suggestions everyone - looks like you've confirmed what I suspected. Building small and cozy isn't as simple as it originally seemed to be.I think commercial systems are way overboard for what I will be doing, looking at a Kitchen Aid or Bosch 600cfm hoods, trying to keep the design minimalist doesn't lend well to commercial duct heater integration and frankly, I hope we don't burn enough food to require 600cf on a regular basis.I'm leaning towards a geothermal loop that will bring air in from outside the house away from the kitchen/living areas at the site of my solar collector array and then using 10" PVC temper the air in underground loops (probably only 200' worth of linear length of pipe) and then into the basement mechanical room to a water heat exchanger and then into the the joist cavity to some floor registers. I envision a passive system but I'll have to really do some math to figure out average cfm and what I really need to provide enough air to make it worth the effort. I guess this is where the pressure sensor air handler comes in then...I'd do all this but wouldn't buy a duct heater??? Just trying to think of a passive solution that wouldn't require a lot of energy. My climate is high desert and cold, cold, and more cold in the winter but not too hot due to 6000' elevation in summer. Outside air is normally 5 to 10 degrees below zero at night and less than freezing most days - but the sun is always bright even in winter - but air coming in is COLD! thanks - sorry for the novel
Haystax,
Buy a small range hood (150 or 200 cfm) and don't worry about it -- crack the window a little if you're worried.
It is incredibly hard to find a decent range hood that is less than 500 cfm. I'm designing a kitchen and a client wants a downdraft hood. I'm not even sure they make those under 500 cfm (I can't find any). Now we have to take a spray foamed energy efficient house and throw a 10,000 w heater (not to mention the power for the blower) into the mix. I can see why they're doing this, but I think the manufacturers (of the vent hoods) need to figure out a solution. With more states adopting the 2009 IRC something needs to be done.
One solution for the hood is to get a commercial style model with provisions for ducted makeup air. Because the makeup air is ducted right to the hood, tempering may not be needed.
Range hood is the easy part
I'd just put in a duct to either side of the range with a barometric dampener so that when the range hood is on, the low pressure will pull in air to either side of the range, wash across it, and up into the hood. I doubt you will be bothered by the cold air entering and exiting at the range. I might install a powered blower system in tandem with the hood controls, so that the make up air to the range is less likely to get pulled in by the bathroom fans.
The bathrooms will require less volume, and you should be able to do them with duct heaters, and air to air heat exchangers. Again, I might look at a balanced blower setup so the make up air is brought in by a fan tied to the exhaust.
Simple
"Building small and cozy isn't as simple as it originally seemed to be."
Well, I can't address how simple it seemed to be, but if you'd lose the unrealistsic idea that a "robust" kitchen exhaust hood has a place in a smart or energy efficient home, the rest would be easy.
You want a science project or a practical and efficient home? You can't have both.