I can't speak for your specific situation, but we didn't install conditioned air with our make up air (1000 cfm hood). For the relatively unusual and brief (15'ish minutes?) instances where we run the hood on high (steaks, burgers, etc) it doesn't seem to be noticable when its well below freezing out (we live in Pittsburgh). Our MUA comes into the basement. Our house is fairly big (~4500 sq ft) and old (built 1903).

Thanks for your input @DrB477. Our HVAC contractor mentioned that if we don't condition the air, it could crack some part in the furnace because of the significant change in temperature. Was that ever brought up to you?

Our MUA comes into the basement (which is a little drafty to begin with). Our furnace is in the basement but the MUA does not plug directly into the furnace (which we were advised against doing) it just dumps the air in the basement. Basically to my understanding, when the MUA is on its like opening a window in the basement. I don't see anyway that could "crack" the furnace. For maybe a total of an hour of full strength hood time a week, if that, it didn't seem worth it to install a complicated heating or cooling system. If this were a commercial kitchen, sure. Now that we've been through a whole winter which was at times pretty frigid I feel pretty comfortable with that decision.

Very cold air ducted directly into the intake could possibly crack a heat exchanger. Most cold climates are adopting the HRV requirement for large outflow/inflow hvac systems. It’s why ventilation can easily cost more than the range.

@DrB477 Can I ask if you recall what you paid to have that makeup air system installed? The ones that have been presented to us are ducted directly to the intake, as Sophie mentioned.

I don't remember exactly but wasn't too bad. More than $500, less than $1k. From this forum I was prepared for MUA being a huge deal, but it really wasn't. Basically it was the cheapest thing intended to meet code in a house that was big and old and (most likely) didn't really need MUA in the first place. Again, I'm a home owner, not a HVAC contractor and I don't necessarily advise this approach for your specific situation but its been perfectly fine for us.

Cold air doesn't crack a heat exchanger in and of itself. The tensile strength of the material of the heat exchanger wearing out is what cracks the heat exchanger. They call it old age.

A heat exchanger for the most part during normal operation of the gas furnace is heated to around 150 degrees of heat coming off the heat exchanger via air blown across it. Surface temp of the heat exchanger may approach 200 degrees. Heat exchangers are not made out of plastic.

Have you ever cracked a window on your car driving in blistery cold with your car heater on?

So what causes a heat exchanger to crack then?

Normal operation and old age. The constant heat up and cool down. Take out a paper clip and start bending it back and forth. Keep doing so and what happens to the paper clip?

It breaks. Just after it breaks put your finger on the part where it broke. It will feel warm to the touch, because the friction of you bending the paper clip back and forth produces energy, the same energy more or less that is produced by heating the heat exchanger of your gas furnace.

Don't believe this: look to the warranty paper work of your furnace.

Does it say 'Blowing cold air across heat exchanger will void your warranty'?

No it does not. Heat exchangers are typically warranted for 20 years, cold weather or not. In fact some manufacturer's will warranty your furnace for your entire lifetime.

Do not reduce the CFM of your hood.

Sufficient MUA must be brought in to your kitchen from outside of the house, otherwise you risk backdrafting other gas appliances like your furnace, your hood will not work as well, etc. The best option is to bring it in, condition it, and send it directly to the kitchen through vents.

However, many other options can work well enough such as the above of bringing it in to a basement where there is a clear air path from basement to kitchen (and some codes/inspectors will correctly not allow this if there are any doors between where the air is brought in and the kitchen). Keep in mind that without conditioning this could make the basement really cold and in summer really hot and humid. This could also make your entire house less comfortable.

I don't know that I would bring it in through the HVAC system. That was done 15 or 20 years ago but I've not seen it done since. Part of the problem is that the static pressure for the MUA is greatly increased (and so the effectiveness is greatly reduced) if the furnace blower is not also running at a minimum of the MUA rate (E.G., 750 CFM). OTOH, it does distribute the fresher air throughout the house with the hood exhausting more stale air.

One question that needs to be answered when considering an existing furnace/boiler to heat MUA is: Does the heating capability (BTU/hr) equal the MUA flow rate times the density of air times the specific heat of air times the desired air temperature rise? (All the parameters have to be in mutually-consistent units.) Expect to need more than a 100 kBTU/hr capability for high flow hoods in cold locations.

A furnace sized for a large drafty house while providing a high hot water flow rate may work, but a furnace sized for a well sealed well insulated house in concert with a separate hot water heater would be expected to be sized for the heat loss of the house and not for hundreds of CFM of cold air.

The most inexpensive heated MUA I can imagine is a damper controlled duct from the outside to a basement (or even to a mud room) with a large Modine style local air heater, along with a reasonably large section air path to the kitchen. The heater would be hydronic, if the furnace is a boiler type, or gas fired, or electrically heated. Residential MUA tends to be unique to the particular home circumstances, so no simple or single answer is generally applicable.