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Comment by nkingsy | Hacker News Reader

This is especially pronounced at high altitude, and when running a furnace in the winter. I keep large black tents (4x4 ft or 2x4) in every bedroom in the house, and grow kale, spinach, chard, peas, tomatoes, etc inside (with handmade COB LED lights).

I don't have any sensors to get a real idea of the difference in CO2 it makes, but it allows us to run the furnace less at night (heat from the lights), and makes a noticeable difference in humidity ( very dry air here ).

Also, we get about 1-2 family meals / week of food at full capacity ( total 4x8 grow space and 800 watts of light running only at night ).

Not economical and takes a lot of maintenance, but it's a fun hobby from which we all feel the benefits.

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Have the police visited? Sounds like the sort of thing they'd think would be a grow house. (....a marijuana grow house, I mean, not one for eggplants and radishes)

I reckon it would be tough growing eggplants indoors with LED light.

Fruiting plants are a pain because you have to shake them to pollinate. We mostly stick to leafy stuff. The lights are incredibly bright, top of the line horticultural COBs. They are not the pain point.

800 Watts for 12 hours a day is about a hot tub worth of draw.

It's unlikely you'll have a noticeable difference in co2 levels with indoor plants, even considering your unusual setup.

I think it’s as simple as biomass produced vs biomass consumed, and I agree a 4x4 garden is not going to fully replace O2 for two sleeping adults. I’ve experimented with building tower setups which would allow 3-5 times the biomass growth in the same space, but it’s a real pain tending to a garden at eye level, and introduces all kinds of new catastrophic failure possibilities when you have water above high power lights.

Nurses used to take plants out of hospital wards overnight because photosynthesis (input CO2 output oxygen) only happens in the daytime, leaving just respiration (input oxygen and output CO2) at night.

> but it allows us to run the furnace less at night (heat from the lights)

Dear God, what's your power bill? There's no way a LED lights heat is as efficient as just using the furnace.

edit: I meant cheap, not efficient.

Assuming the furnace is electric too, they should both be the same efficiency, since 100% of the power is being eventually turned into heat, unless the light from the LEDs are going outside.

I never considered an electric furnace - I come from a land of ice and snow and the only real option is natural gas.

I live in a land of ice and snow and we rely entirely on mini-split heat pumps in the winter [1]. Admittedly they do lose efficiency quickly when temps drop well below freezing, but they work well enough here.

I have also seen some pretty cool looking "passive" houses that, due to excellent insulation, are able to heat the entire house with a 3kW furnace [2]. And these are in very cold locations (e.g. Alberta, Canada).

Electric heating is the future!

[1] https://learn.compactappliance.com/mini-split-heat-pumps/

[2] https://www.youtube.com/watch?v=AlA4_lesrU4

I live in Alberta - I love the idea of a passively heated house, but for now I'll stick with my 25 kW (converted from BTU) gas furnace. It's about 5 cents / kW for electricity and 0.5 cents for natural gas. That house would still cost more to heat. Sadly natural gas has a carbon footprint by default.

What you want is not an "electric furnace", which uses electrical heating elements, but a heat pump per one of the other replies.

Mitsubishi has some that can extract heat from the outside air even down to -30C.

Most though only work down to about +5C (they're used in more temperate climates). So check the specs.

They also work for AC.

The highest BTU heat pump I see is 46,000 - that's not going to be a solution for a lot of homes, which need 30,000 / 1000 sq ft, not to mention loss in efficiency as the heat drops so you're getting less than that when you need it the most.

How much you need to heat/cool a home is more of a function of its level of insulation and air tightness than its mechanical capacity.

It's possible to design house that need almost zero BTUs:

* https://en.wikipedia.org/wiki/Passive_house

When looking at bang-for-buck / value / ROI, better insulation and air sealing should be done first. If you can reduce the number of your blower door test, then you'll have to spend less on running capacity (and their related costs).

Passive houses are cool, but most houses aren't, and can't be retrofitted to fit the requirements.

True, but they show that comfort is possible without crazy mechanical power. Improve your insulation first, and you'll need less BTUs afterwards.

So, assuming you have an electric furnace, it basically costs nothing to run all the electronics in your house? (Also assuming it's cold enough outside that you never want to cool the house.)

I guess the water heater might cost some money, since it produces heat, but a lot of that heat just goes down the drain with the water.

Theres no difference in heating efficiency for any source. Heat is heat and it doesn't really matter if it's generated from a heating element in a furnace or an LED light. And with the light you're at least getting dual use out of it.

If they have a gas furnace it might be different but that would also depend on how their electricity is generated.

Yeah, I was thinking gas furnace. Also the heat would be localized to a couple of areas and not the whole house heat that a furnace would probably provide.

except a heat pump which is far more efficient

Until you get to below zero.

They now (as of 2018 I think) make Extra Low Temp heat pumps, which can work down to -15F. I think that makes heat pumps practical for a very wide variety of temperate climates.

I see they do, but their BTU's are very low - I see the Fujitsu RLS3H, which goes down to -26C only outputs 12,000 BTU at that temperature. To heat a house at that temperature you'd need 5-10 (if not more) of those.

Only if you insist on the same duty cycle. Furnace might only run 4h/day, while heat pump could run all day (6* reduction)

I don't think that's quite true. The efficiency merely falls to 100%. (The laws of thermodynamics demand it.)

Now, converting electricity to heat may not be as cheap as converting, say, natural gas to heat (thus making the heat pump un-economical when not pumping any heat)... but you do get heat out of it.

That's true. But heat pumps don't have the gross energy capability as a gas heater. To get the equivalent of an 85,000 BTU gas furnace you'd need to be pumping 25 kW through your heat pump at that point.

I think one reason heat pumps have become more practical is that homes are now better insulated, making 85kBTUs of heating capacity excessive for all but the largest houses.

We've got an old, poorly insulated home which is why our requirement is so high.

The average is 30 BTU / 1000 sq feet. That's 10 kW / 1,000.

Your statement is true if the electricity is generated locally, otherwise there's a difference in energy losses depending on the carrier.

According to http://web.archive.org/web/20180822025250/https://portfoliom... heating with grid electricity would require 2-3 times as much primary energy as heating with water/oil/gas.

Especially if you have central heating.

Extra $38/m, and because the heat is targeted we can leave the unoccupied areas colder.

Certainly not an efficient way to heat the house, but the main concern is oxygen and not generating co2 with the furnace, then air filtration (SLC nasty air), then humidity, then food, THEN heating.

edit: we vent the tents directly at our beds

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