1. where do they go? Well, you have options. First of all, the idea is to bring outside air into the house. So they 'go' from the outside to the inside. On the outside wall you will probably need a screen of some sort/size to keep critters and insects out. Somewhere along the path you will need a filter box like the one you have for your HVAC unit with filters that you will replace from time to time. If you live in a cold climate, you will probably need an inline heater of some sort for those cold days.

Now, some folks connect the pipe to the supply (inlet) side of their HVAC. This lets the HVAC cool and dehumidify in summer and heat in winter, and do so directly. Others send the pipe to a vent in the kitchen (or nearby) in the ceiling, floor, behind or under the stove.

A 'damper' is something that opens and closes to control the air flow. For MUA, this is usually something (a flapper) that is either electrically activated from the exhaust blower switch or barometrically activated by measuring a low pressure in the house when the exhaust blower is on. The second one is passive.

2. do you already have one? Maybe. Maybe not. The codes for this are fairly recent and may not have been in place where you live in 2000.

3. Who installs? That's still up in the air (pun intended) somewhat. I think of it as an HVAC thing since it deals with duct work. It's also a bit more involved than exhaust fan installation and routing. The HVAC people should be able to do it as part of new construction. They may not be interested for remodeling since there isn't that much duct work involved.

I can only add at this point that where the MUA intake is best located, and where the MUA outlet in the house is best located, is very house layout specific. The question of who locally to obtain advice from is similarly location dependent.

This forum has accumulated many MUA related threads since, at least, 2008, and some of these address particular configurations that may provide some insight. Here is an example with some photos.

http://ths.gardenweb.com/discussions/2266424/does-this-sound-right-re-mua

kas

Installing for automatic makeup air is not required where I live. Also I live in the south and in a rural area. We have a kitchen window just 4-5 ft from the exhaust fan and so just open the window when running the fan. Just cracked slightly open on very cold or hot days and it is enough.

Edit: I should also say that I would have loved to have automated makeup air. Spent a fair amount of time thinking about doing it - location, configuration, etc. But in the end, went for the manual version.

If combustion appliances are involved without their own MUA sources, and one is using the window (manual) MUA method with a hood blower rated at the higher portion of the usual CFM range, having a differential pressure meter would be a good idea. It would be easy for a window cracked slightly open, as well as for a screened window opened significantly farther, to allow more than 0.03 inches w.c. of house negative pressure to develop. Beyond that safety limit for such appliances, backdrafting of CO is possible.