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Adding HPS/MH to the room for the winter.

Hello yall! Currently using leds, and love them. However thr electricity savings get shot out the window when adding heaters to the room during the winter.

I'd like to add a HPS or a MH light, just for the added heat. If I'm paying for heat, might as well get some light out of it.

I'm sort of leaning on a MH light to veg in the room at 18/6, over a HPS at 12/12. I'm really not interested in running autos at18/6

After getting over the learning curve of LEDS, I'm a little nervous of this.

Has anybody seen how a plant reacts after being fully vegged to maybe a foot tall under MH,then transfered under LEDS to flower? Of course the leds would be looooow for a bit, but stressing the plant going into flower is something I avoid like the plague lol

Anybody ever done this?


Well-known member
I like using High-Intensity Discharge lamps during the Winter too. Instead of turning on the heaters, I just allow the HPS lights to warm the house. Now you can use a combo light system where LEDs and Hps are used in the same grow. My fav is a 400 HPS mixed with 1000 watt LED. Every time I have ever mixed HPS and LED the plants responded like fricking crazy. It's still too hot for me to use a combo but when its time for a heater I'm adding HPS to my LED grow. 😎


Well-known member
One way to control temps and humidity with leds is by not having your exhaust running all the time.

I use a timer on my exhaust – during winters it goes on for 10-15 mins every 1½ hours or so. It’s rather cheap and easy way to keep temps and RH higher during colder seasons.


Well-known member
coconaut, one thing i was contemplating was using vert cmh bulbs in between leds to act as a heat source.

running the cmh bulbs / system on a separate circuit off my hydro x pro controller with a par sensor.

while this only helps during a lights on scenario, if the room calling for heat or additional dehumidifcation (reheat) , the controller would activate the cmh lights. Instead of the energy being used to run a heater, or dehumidifier, the energy would go towards the cmh bulbs creating wanted heat and .........usable light. A heater or dehumidifier do not create usable light! So i see this as a more efficient way; or at this point in theory. A bit more confusing to some, but could be a tool to gain efficiency as costs for producing are go up in most areas, and price of the product is going down.

Also during a lights on scenario, if the room was calling for de humidification the cmh lights would turn on as well. The increased heat would be added to the room and at some point the extra heat would make the air conditioner(mini split) start to ramp up and cool. As a by-process of cooling the air, the moisture rate of removal would now increase, and continue to increase on a sliding scale as the ac speeds up, hopefully matching the rate of removal desired to the plants transpiration rate.

Now that the CMH lights are on, the hydro-x pro controller par sensor will now see an increase of ppfd/ DLI starting to ramp up, and now the controller will now maintain PPFD and lower the led's output, matching the set ppfd. In turn lowering the elec usage to led's. Maintaining a similar photosynthesis pattern/ growth, water consumption pattern. (But increased Infared from cmh) Still A fair , better, trade off......

Importantly, the controller will now lower the LED light output/wattage to match the set ppfd. Utilizing the electricity in a far greater way then running just a elec heater. The led electricity use goes down, and the cmh wattage use goes up, but there's a wonderful give take scenario that in my eyes would be a great trade off.

Hopefully stabilizing the temp an desired humidity. I can think of a few other things to add that will change but for sake of me not making this more confusing i will leave them out.

This definitely would take some tinkering to get "X" ammount of 315w cmh bulbs to match the desired heat btu add back demand. And then learning the deadband adjustment to prevent the cmh bulbs from cycling on an off. For a start you could atleast start with going off how many btu's each 315 cmh bulb will add to the room. And add or subtract bulbs accordingly to get some sort of stabilizing.

the de-humidification part is important in my eyes, to the fact that a properly setup ac system can remove excess humidity far more efficiently then a dehumidifier. The mechanical energy loss is great in a dehumidifier, and it also adds heat(which wwe do want in this scenerio, for now). Also one less piece of expensive equipment not having a dehumidifier. It is far cheaper for adding an elec heater, or adding heater coils in a air handler, or running a propane heater, as the heat source during lights off. Letting the ac do the job. And of course, this is all possible if the ac system is matched and setup properly.

((However this could all be Rube Goldberg, and it maybe better to go with a room design from the start that ran the LED and CMH combo together.... always. Design the room so that the led's provide 100% of your lighting needs. then add the cmh to the system based on desired btu heat demand needs. a system that say only relies on an additional heater maybe 1 winter month out of the year, say febuary in the northern hemisphere. the light combo is stable without a heater an additional 6-8 months, before you winter, during most of winter, and then after winter. And maybe then shut the cmh in the middle of summer)

(An example, say you are running 6 led lights with bar strips. 2 lights side by side, 3 lights deep, lights are in parallel. Start by placing 3 cmh bulbs in the system. My first instinct is to place the cmh bulbs in the areas that receive the less ppfd, but, those areas are usually between the lights or on the outskirts of the lights. Bare bulbs on the outskirts can be far more dangerous then if they where in the interior of the array. On the out skirts u can bump into them easier, or theres a greater chance for something to fall onto them like panda plastic if it was to come dislodged. Finding that ratio of how many cmh bulbs to led lights defintely would be solar location and outside temp dependit, then your heat loss of the room. it maybe a 1:1 ratio 660w or 720w led to 1 315w cmh, maybe its 1 led to 2 cmh. I think this is a very interesting design topic all together ))

And as corpselover said, more insulation will definitely help. With the increase of electricity and heating expenses, it makes sense to spend the money on proper insulation for all the seasons.

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