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Comment by sjg007 | Hacker News Reader

New homes have ERVs or HRVs and some have ventilating dehumidifiers. You could put an AQI sensor on it to run them as needed but generally they are either timed per hour and on a humidistat. New homes also have to have gas appliances (except for the stove) with their own air intake and powered exhaust.

All gas stoves should be below a hood with a ducted outside vent, the more powerful the better.

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> All gas stoves should be below a hood with a ducted outside vent, the more powerful the better.

To my understanding, installing a very powerful stove hood in a tightly sealed house without proper consideration for a make-up air intake can cause problems (i.e. backdrafts in the exhausts for gas fired water heaters), especially in concert with other things venting outside like a clothes dryer. It's very possible to have it done right, but a pretty bad situation if done wrong.

Newer gas fired water heaters (mine is 10yr old) with closed chamber have special chimneys where your exhaust and intake go through double walled pipe with counterflow, which helps with energy recovery (exhaust goes through inside pipe, fresh air goes in outside pipe and gets heated by exhaust gases). That also means you don't need to have proper intake where the heater is (but there still needs to be some ventilation).

Yep, it is subject to building code requirements. This is why installing ducted vent hoods usually requires a permit etc...

I'm not familiar with those acronyms. Googling suggests ERV = Energy Recovery Ventilator [0] and HRV = Heat Recovery Ventilator [1]. Wikipedia says these are mostly about energy efficiency but also have air quality benefits. It's not clear to me how this helps with indoor air quality - maybe better humidity and temperature regulation?

They also seem to require a centralized air conditioning/heating system. That would give you a nice central place to put an air quality monitor. The big challenge though is that often these central systems don't process all air in the building evenly. Multi-zone systems help.

1000% agree on the venting. It occurs to me that I have some gas heaters that I should double-check the venting on... [0] https://en.wikipedia.org/wiki/Energy_recovery_ventilation

[1] https://en.wikipedia.org/wiki/Heat_recovery_ventilation

Having a heat exchanger let’s you exchange large quantities of outside air with indoor air at minimal costs. Trading 70f indoor air with -30f outside air is bad, moving heat between them means could be venting air closer to -10f and only need to heat the new air from 50f to 70f

You still want a quality filter and humidity is an issue in some areas, but overall they can make a huge difference.

Wouldn't a heat exchanger top out at equalizing the inward and outward bound air at 20F in this case?

The idea is "countercurrent exchange": the incoming air and outgoing air travel in opposite directions through the heat exchanger. The result is that most of the heat gets transferred.

At the end of the exchanger, the warmed incoming air is in contact with 70° outgoing air, so it will be at almost 70°. Similarly, the outgoing air will be at almost -10° as it exits.

It will probably make more sense if you look at the diagram: https://en.wikipedia.org/wiki/Countercurrent_exchange

Fun fact: "An example of countercurrent heat exchange occurs in the feet of penguins, in which heat from blood in the arteries supplying the feet is transferred to blood returning to the body's core in veins that lie close to these arteries."

No. Imagine that your heat exchanger is simply two touching pipes running parallel to each other, with flows in opposite directions. Incoming air will gradually warm up as it comes inwards, eventually being warmed by the air which has just left the room. You can get a much better result than just averaging the temperatures.

They are called air exchangers, basically the replace indoor air with outside air but pre-heat the outdoor air using a heat exchanger off the indoor air. So AQI definitely improves when they are run.

My house basically has a natural set point that the exchanger runs at per season. Much like my thermostat I can basically leave it at a setting for a season and it works well.

There are a few days I may have to slightly adjust things, usually when there's a big temp swing, so if it were more automated that'd be better but in general I have to maintain conditioned air in both the winter and summer to keep the house stable... and the house seems happier for it.

One can install HRVs and ERVs with no centralized system. We have, oh, three heat sources and half an AC in our house (old house) and can install a freestanding HRV or ERV simply as an air exchange (bringing in fresh air and letting out stale air). As we live in a cold climate, we're working out what we need in terms of HRV vs ERV. It seems like a slightly better solution than "leave the upstairs window cracked" which is what we do now.

New homes have ERVs or HRVs

What country are you in? I'm in the US and my nice home, built in 2015, doesn't have either one.

As far as I know they only put them in the super expensive houses that are made extremely tight. If they use spray foam insulation then there is very little air circulation so that they need to add an ERV just to get enough air to breath.

Check your code requirements. I am in the USA and they are required, but I am in the north where we have very cold winters and humid summers. You should consider putting one in if you don't have one.

I'm in Pennsylvania! But maybe that's not north enough for them to be required.

What part of the country are you in, and what price range, where new homes have ERV or HRV installed?

I'm in Kansas City, and even into the $650k range, houses only VERY rarely are built with them.

20 years ago the building code in MN required them, or some other form of ventilation. (leaving the bathroom fan on constantly would probably meet the letter of the law, but no contractor I know of was willing to try to get past the inspectors). Different states have different codes, so and I am not up to date on what the latest is anywhere anymore.

A lot of places building codes "require them" at a high level, and then more local building codes strike provisions like this, or provide "alternate paths" to legality. It's disgusting.

Like around here, the building code in one city requires a certain blower door score to pass. But doesn't require blower door testing if you say you followed certain "sufficient" practices. There's no way most of these houses would achieve a sufficient blower door test score, but they all "comply with code".

Are there any quality brands that have a vent that can be directed outdoors? We're renovating our kitchen in the next year and are planning on doing this, but haven't had any luck finding a natural gas stove which is made to vent outdoors.

I don't have counter evidence on hand but assuming the oven is vented outdoors, my understanding is that a hood should be relatively low-powered, not high, in order to then capture emissions from the stove top. It should be a function of size, height from the stove top, noise constraints, etc.

You can calculate the minimum CFM required to vent your stove top and oven based on BTUs and room size. Your CFM calculation will also inform duct size and make up air requirements. Lots of sites do this but here's one.

https://www.prolinerangehoods.com/blog/cfm-need-range-hood/

You can vent both the gas oven and the stove separately. You have to buy high end appliances for that. I've seen them but can't remember.. maybe a Viking stove or something prosumer-commercial. Make up air can be a cracked window or a separate intake duct that opens up when the vent is turned on. Your local building code will have specific requirements.

You can duct a hood out of an external wall or even better out of the roof. If you go with a roof vent you can install the extractor fans in the duct in the attic which helps reduce noise if that's a concern. What you can do will depend on your specific kitchen.

I have found that the stove top is worse than the oven for emissions. The reason is that my exhaust hood is under-powered and it's a microwave/exhaust combination that doesn't extend over the entire cooking surface. So I would advise a hood larger than the stove top itself, install a larger duct and I would overestimate the CFMs required. If you get a multi-speed range hood then you can adjust it as necessary.

I actually think electric ovens are better combined with a gas stove top. Electric ovens though do have a tendency to fail at inopportune times (e.g. the holidays!)

> All gas stoves should be below a hood with a ducted outside vent, the more powerful the better.

The best part is how many "down draft" vents are put into place, even new luxury construction.

They look nice, but don't do much...

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