Hi there snafu,

The damper is a good start, but you most likely will need a bit more air at your peak flows. If you don't care about conditioning the incoming air, all you need is a damper and blower for you MUA "package". A silencer might not hurt, and don't forget the filter holder and filters. They are cheap and easy to find on amazon. A blower is about 500 dollars for your application. If you are hesitant about needing the blower like I was, you can always build you MUA system with a blank length of duct that would be easy to switch out for a blower if you wanted one. You're going to have a great setup when you are done, good luck!

@catinthehat

"If you don't care about conditioning the incoming air, all you need is a damper and blower for you MUA "package"."

Well that's the thing, we have cold winters and hot summers, which is why I said that it made sense to me that the damper system would hook into the return for our HVAC system, then wouldn't it condition that air (warm it or cool it)? Or am I missing something?

The Fantec system seems to be wholly self-contained, with silencer, blower, heater etc, is that accurate?

Okay in that case, and I'm not an expert on this, you will probably need fantec's package. My understanding is that normal home central air is not capable of heating/cooling the incoming air fast enough. Others may chime in to confirm here, but the real experts will be on HVAC forums on some other sites. Sorry, I live in socal and haven't had to research this.

In most houses, the heating and cooling systems are designed for relatively low leakage houses. They may have only limited heating and cooling performance when dealing with 1000 CFM of air replacement. Very likely at that level of kitchen ventilation, the HVAC return will be moving air in reverse unless your house is very large with a high flow HVAC system.

One might connect outside air to the HVAC system to handle the times (most of them) when the hood blower is running at a low speed. At higher speeds and lower house pressures, another damper could open to supply MUA more directly. Conditioning this air to the degree desired would be a project perhaps best allocated to experts.

@kaseki Hmm interesting...incidentally, other than the new kitchen add-on which is tight, it's just a drafty old farmhouse so I wouldn't call it 'low leakage' by any stretch -lol. It's a big space too, 3000 sq ft and another 750 sq ft of basement/crawlspace, I don't know how much that helps but that's what we got

So are you saying:

1)on low (say 1/3 power - 400-ish CFM) this damper hooked into the hvac should work well

2)on med-high, our hvac will not be able to handle the additional flow of it's regular duties + the hood and a secondary system will be needed?

We just have a damper and live in Ohio. If the exhaust is on for awhile, it can get chilly in the winter, but our range puts out a lot of heat, so its not much of an issue. In the summertime when we have the A/C on, it can make it a little more humid inside, but I don't really notice the heat.

@stavishwatson That was sort of my thinking as well. The problem is that everyone is trying to sell you on something more that you don't necessarily need so it's impossible to decipher if they have a legit point (and an expensive system is warranted) or they're just trying to cash in on a commission. It's really sad how little integrity is left in the business world

If you're in a cold climate, you should think about an inline heater. Usually electric and thermostatically controlled, it can raise the temperature 40*-50* (check the specs) depending on the air flow rate. If really cold, then maybe two in line.

The description of the damper says that you might want to think about two of them in parallel, with the 2nd set to come on at a higher flow rate for additional air.

Not everybody uses an in line fan. Some systems are passive, but they require some study to make sure that the flow losses aren't too bad, ie, the size of the inlet screen, restriction of the filters, etc.

Some will dump the air into the HVAC system, other dump into the kitchen either behind the stove, or the ceiling, or a far wall.

Ultimately, the issue of interest to code enforcement is back-drafting of combustion appliances. There are a lot of ways that the MUA path can be restricted enough to cause a house pressure drop of a mere 0.03 inches of water column. Without a lot more knowledge of the entire house systems and layout, all is speculation.

For example, suppose that you pull 1000 CFM actual through a damper controlled otherwise open path. How much dust, how many bugs, mice, and sparrows are acceptable. If you use any filtering, like that of a hot air furnace, you will cause enough restriction that an MUA blower is needed to keep the house differential pressure below 0.03. I think a mere window screen covering the duct diameter would be enough pressure loss.

If there are no combustion appliances, or the house can manage 500 CFM of leakage at 0.01 loss, then that is a lot different than the alternatives.

How many CFM is your furnace rated for?

We are at the very end of a big renovation and have a 1200 cfm hood. The mua will just be a damper that dumps into the return of the HVAC system. I went through all the same thought processes that you are exploring here but in the end decided to start with this (very inexpensive) set up because opinions from varying sources on what was actually needed (beyond code) were all over the place though this was the most commonly recommended so figured it would be a reasonable starting point. If I'm disatisfied, I'll explore something like the fantech system. In the interim I've just opened a window on the few occasions that I've turned the hood up pretty high.

A few more data points:

I'm in Chicago so get the very hot and very cold.

House is 40 years old so not tight.

Room is probably 700 square feet and wide open.

Combustible appliances are down in the basement in their own room.

There are 2 fireplaces on the first floor, one is in a closed box

Let us know what you decide, I think the potential complications that Kaseki mentions that are also unique to each house cause many HVAC pro opinions to fall back to code. So many I talked to sounded like they were just guessing when I asked about heated or blown mua.

@pauls234 This is exactly what I'm looking for...not speculation, not salesmen trying to sell me something I don't need, just a real life example that I can relate to. Thank you.

pauls234

The configuration that solves the safety problem, even if it doesn't solve robotic code enforcement, is to have the combustion appliances operating with their own MUA in a room "sealed" (practically speaking) from air paths that get to the kitchen.

In such cases, performance-wise, kitchen pressure drops due to inadequate, or filtered but unblown MUA, will only cause degraded hood blower flow rate. Other pressure issues, such as pulling moisture into walls, is another issue.

I am constantly amazed that folks have the money to have these high end appliances / ranges / hoods / and don't want to spend money to do it the right way.

@geoffrey_b who says it's 'not right'? pauls234 has an almost identical scenario to my own and it works great for him. Why would I go out and spend $2500 when I probably don't need to? If I do find out that I need more from my system or that the cold air is a problem then I can still tackle that in the future.

If the combustion appliances are protected, but the fireplace isn't, the use of the hood and fireplace at the same time is not recommended unless the MUA is very well balanced. Here is a contribution from another commenter here.

The bottom line is that this is all idle speculation...every house is unique: the layout is different, the sq footage is different, the age and 'tightness' of the construction is different, the HVAC systems in place are all different.

Whenever I'm unsure on a question like this I always ask 'what's in it for them'? In this case, I've got a salesman who wants a commission on a $2500 system that I may or may not need...that's his motivation. Then I have the HVAC company who has recommenced a simple $200 system...they COULD have recommended the same system and tacked on their fee but they didn't, why not? I'm leaning towards the professionals who have actually walked through the house and examined the parameters.

Then I can only recommend that the minimal installation be configured in a way that doesn't require any household de-construction if a blower or heater are deemed necessary after sufficient experimentation. Dump sufficient cold winter air on the dear-wife's toes and you will learn another definition of "necessary." :)