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I have a small technology business and have moved a rack of computers into my home from my office. These computers are duplicates of production machines for backup and replication use only, so they do not require a data center like environment. That said, they still run 24x7 and produce a great deal of heat. Unlike deflecting a dryer vent, the output air is clean and dry, so it would seem safe to me to deflect this heat back into my home heating system. That said, I am not an HVAC pro and would be very grateful to receive any feedback on the concept.

Some details:
  • I plan to locate the severs in a closet [built for this purpose] that is within 5 feet of the furnace. Everything is in the basement. The closet would be part of the finished basement area. The furnace and hot water heater are in an unfinished room of the basement.
  • It's a forced air system
  • I would install some type of deflector that would route the heat outside during warm months and into the heating system during cool months.

Questions:
  • Am I crazy? If so, why is this be a bad idea?
  • If this makes some sense, should I connect the hot air into the system's return or the furnace output? My concern is if I connect to the return, when the furnace is not running the hot air will blow throughout the house's return vents. However, I don't know if that is even a problem?

Thanks in advance,
JL
 

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Seems like it might work, If your closet is enclosed and finished, meaning sheetrock and tape to seal the room. Then add a 12" duct to the room with a 12" fan blowing the air out. You could add a wye in the duct to direct it outside or into existing ductwork.
I have never done anything like this before, just bouncing ideas out.
I do realize how much heat can be generated and would be nice to recycle that heat.

First problems I see with my idea above
1:, 12" may not be big enough to evacuate the heat out of the closet, you may need to have 2 ducts.

2:, what happens when the furnace kicks on and blows heat back through the duct into the closet?
Need to make it one way somehow and not sure how you can do that.

3:, A simple fan with a on off switch would not be ideal to control the fans with.
There are attic fans available that turn on automatically when a certain temp is reached and may be better for this.

I have thought about doing this but with liquid cooled pc's, would have the radiators to control the heat.
I have a friend that built a litecoin miner, is a I7 with 3 gpu cards and could add more cards to it, is just maxed out on heat and at the stage where it would be unstable if he added more to it.
He has a home made cooling system now with coiled copper sitting in a laundry tub full of water, he adds more water to the tub as it evaporates.
That room is 12' wide and 25' long and is like a sauna in there in the winter, unbearable during the summer.
I am playing around with building him a radiator with these.
 

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You cannot add it to the forced air side of the furnace as it is under high pressure and will blow back at you. You could run a round duct 6" and with a under 100 cfm fan and park it under a horizontal or vertical section of the return duct. Should be at least 3" away from the furnace fan though (important). Then cut a register with a built in damper (3"x 10" floor register ) into the return duct and park your 6" pipe about 4-6" away from it and let it suck the heat into the return duct. we do this with HRV's sometimes. Then you can shut the floor register in the Summer and come up with another outlet for the heat to the outside by putting a tee in that pipe and damper it closed for Winter. The small amount of heat that will blow thru the furnace vents is no problem. If it is a massive amount of heat it could overheat the furnace when it is running and you should check the furnace temp rise when running but I highly doubt that is possible. If you can and there is a way to do it find out how many BTU's per hour you will exhaust and get back to us. Has to do with the wattage of the computers and you can translate that into BTU's. Google that or Beenthere my Buddy can help with that. Somewhere in this site you can find good info on that. There are fans available under 150 cfm with ECM motors so you can use a rheostat/solid state speed control to slow them down. Have to search the web for them.

http://www.engineeringtoolbox.com/duct-friction-pressure-loss-d_444.html
 

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Just curious why he couldn't tie the duct from the computer closet directly into the cold air return trunk with a wye to outside for the summer months?

I would do that and place a duct fan in the 6" pipe running continuosly into the cold air trunk in the winter. I see no problem with this pushing air in that trunk when the furnace is off.
 

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Discussion Starter #5
I looked up the manufacturer specs of my servers and the sum of all is 27,946 BTU.

From everyone's comments so far, I gather that the closet must connect to the existing system return vents. Connecting to the furnace's output is not an option due to the high pressure at the furnace. Another reason is because the furnace when then blow hot air back into the closet.

As for the fan, I think a simple "always on" fan is good enough. This is because the servers will always be powered on and always generating the heat. I don't think there is a need for it to kick on at a certain temperature, because it will hit that temperature within minutes; especially when I enclose the rack in a closet.

bcgfdc3, perhaps I misunderstood the other comments, but I did not feel that anyone stated that I would not be able to install a wye to vent between the cold air return and outside. If I am reading something wrong, please let me know?

I greatly appreciate everyone's comments and welcome any additional. I'll post pictures once the project progresses.
 

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Really they need to be in a dedicated space, with their own cooling system, along with the fact, that you need some type of suppression system in case they do overheat and cause a fire, when they release the magic smoke.

The best way to keep them cool, is to use a min split, and have a bedroom that has the walls insulated, to help keep the heat from migrating into the other living spaces. Also out of curiosity, are they paying the electric bill, that this rack of equipment is using?
 

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JOATMON
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Based on your BTU #, it sounds like your running 3-4 servers. That # you got for BTU is worst case. So, unless your running them bad boys maxed out, your most likely about 25-50% below that figure. A big variable is if you have one or monitors in there as well.

Overall, I think your over complicating this.

Basically, you just need to replace the air in there.

If it was me, I'd cut a hole in the bottom of the door...say 6x12....and the same at the top.

Install a couple of AC powered box fans at the bottom with a filter between them and the grill. Run an SO cord over to an outlet and call it done.

Now...what you did not talk about was the UPS. I personally would not be running those servers straight off house power...I would have something like an APC 2200w UPS for those boys. That will also add to your heat...not much...but will add.

All of this is assuming that your house stays conditioned (heat and cool) all the time. If so...using plenty of circulation will do the job.

One last thing...fans....the reason for the fans at the bottom is to create a pos pressure in the closet. This reduces the amount of dust. You can install them at the top...but now they are sucking...which means air comes in any way it can....like under the door....now you have more dust coming in.

Ether way...fans at the bottom sucking...fans at the top pushing out....cold air in at the bottom...hot air out at the top.
 

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I hope you do keep us informed. I can not speak for others, myself I am interested in how we can reuse this energy. I was going to make a thread in the computer section, maybe it does fit here with hvac.
We do spend the money for electricity to create the heat, why not a way to recycle it?
I always thought a p-4 in the knee hole of the desk running gentoo was a great foot warmer.
 

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You want to suck most of the return air from the house and keeping a gap allows enough to get sucked in w/o disrupting the house. Once your start hard piping it in then it can alter the air flow and suck too much from the comp room and not enough from the house which will cause circ problems in the house. ALL of this is theory and these homemade systems have to be tried to work. 28,000 BTU's per hour is LOTS. That would require a 2 ton AC and will send so much heat to your furnace that it may cause the furnace to overheat as your mixed return temp will be way over the usual 70 deg F. Sounds like you need a mini split 1-1.5 ton unit and build a proper room for your stuff. Or you can just release it into the basement and let it go wherever it wants in the Winter. Hot air rises so that may be the easiest solution.
 

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The benefit that you might get from reusing that heat isn't worth the trouble. Piping it into your existing system through the return may cause more problems than it is worth. The idea of a mini-split is great if you can find something cheap enough to warrant the cost.

I have to agree with ddawg16, I think you are over-complicating this. Cut the fan and vents in as suggested and call it a day.
 
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If that room can truly produce 28,000 BTUs /hr that is a LOT of heat. Stand beside a 2 ton AC and see how much heat comes out > LOTS. Even a 12,000 BTU window unit gives off lots of heat as we had one in our warehouse doing the front office and the warehouse got hot from that small unit. I can heat a small house here with 45,000 BTU's/hr. I wonder if these large home computer rooms are such a good idea considering all that is involved. A house is meant to be lived in not turned into a computer business IMO.
 

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JOATMON
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I must have had a brain fart......I just went back and looked at the #'s.

27K BTU.....are you sure? that works out to about a load of 66 amps.....how many servers are you running?

How did you come up with the 27k BTU #?

For reference...a computer with a 300w power supply can put out 'up to' about 1023 BTU of heat...
 

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I must have had a brain fart......I just went back and looked at the #'s.

27K BTU.....are you sure? that works out to about a load of 66 amps.....how many servers are you running?

How did you come up with the 27k BTU #?

For reference...a computer with a 300w power supply can put out 'up to' about 1023 BTU of heat...
My guess, two Blade Servers, two UPS, then add in a SANS or large scale NAS, Switch and a router.

Sounds a little sketchy to me, especially since they have not been back since they posted. No company is going to co-locate a rack of equipment in someone's home, that is not setup to have a dedicated space in it, with fire suppression, heat detection alarm system, enough incoming power to handle that load, dedicated large pipe for Internet bandwidth, mini-split to keep the space cool that it is located in.

Yep, this was a fun one, but funny how they hit and run, and never come back to continue why and how.
 

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In fairness to the OP, he has stated that he is the owner of the company and not an employee so moving servers to his house would not be out of the question.
 

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Discussion Starter #16
Thanks all for the great advice so far. For those that question/debate the entire idea of bringing this equipment into my home, I really do appreciate your feedback and have thought through much of the same. That said, I think we should keep this limited to a scope of an HVAC project. If you would like to continue to discuss my "why" or other computer related equipment, feel free to send me private messages. I don't want to bore others by turning this into a business model discussion.

Back to the venting stuff:
There are currently 6 servers in the rack and I took the BTU ratings directly from the product spec pages (plus I added 5000 BTU for potentially more machines in the future). Yes, the rating is the MAX BTUs. All have multiple power supplies. The biggest heat generator is an HP DL320S which has 12 hard drives (4070 BTU).

Some have mentioned the cost as an issue. However, unless I am missing something, the costs seems to tiny to install basically about 15' of duct work with a 'T' and a fan. Definitely, tiny compared to the heat that would be recycled in the house.

I am concerned with overheating my furnace by allowing it to suck in hot air. The air that this rack expels is currently between 95-105 degrees F. If this poses a risk to overheating the furnace, I may just take Yuri's advice and just blow the heat from the closet into the basement and let it rise naturally.
 

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I am concerned with overheating my furnace by allowing it to suck in hot air. The air that this rack expels is currently between 95-105 degrees F. If this poses a risk to overheating the furnace, I may just take Yuri's advice and just blow the heat from the closet into the basement and let it rise naturally.

The small amount of heat you would be adding is really nominal considering the fact that it is mixing with your cooler return air so overheating the furnace won't be a problem.

Piping this into the return is fine for the heating season, but for cooling, you will be feeding an additional load for your AC unit to handle. While again nominal, there really are so many factors involved with doing this that you have to start to ask yourself if it is worth it. Fans and vents in the door really and truly make the most sense and will cause the least potential problems.
 

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I looked up the manufacturer specs of my servers and the sum of all is 27,946 BTU.

From everyone's comments so far, I gather that the closet must connect to the existing system return vents. Connecting to the furnace's output is not an option due to the high pressure at the furnace. Another reason is because the furnace when then blow hot air back into the closet.

As for the fan, I think a simple "always on" fan is good enough. This is because the servers will always be powered on and always generating the heat. I don't think there is a need for it to kick on at a certain temperature, because it will hit that temperature within minutes; especially when I enclose the rack in a closet.

bcgfdc3, perhaps I misunderstood the other comments, but I did not feel that anyone stated that I would not be able to install a wye to vent between the cold air return and outside. If I am reading something wrong, please let me know?

I greatly appreciate everyone's comments and welcome any additional. I'll post pictures once the project progresses.

Venting that heat to the outside is a good idea, at face value. Problem is that the air that is blown outside has to be replaced some how. And that often means from outside air. Which in the summer can be high temp and high humidity. Costing more to cool it, then to cool the server area.
 

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Beenthere is correct, once you start exhausting it then hot air and dust get sucked into the house. As far as overheating the furnace no one knows 4 sure but you are free to try. Not a good idea IMO. Some furnaces are cranky and are already running within 10 deg F of tripping on the high temp overload so you may be kicking yourself if that breaks on the coldest day of the year. Not bad if you can do w/o the furnace for a day or 2 but running it too hot also shortens the life of the heat exchanger. You are asking the furnace to do something it was not designed to do. Exhausting the air could and will create a negative pressure in your house and could sucks fumes down the chimney and from a gas water heater and create CO Carbon Monoxide and damage the heater. Also the makeup air will come in your bathroom fans and range hood as those are the easiest places for it. Now you see why it is not the best idea to monkey with your house to that extent. It can be done but you REALLY REALLY got to be careful and know what you are doing.

A bit cloudy today so I cannot tell you 4 sure what is going to happen.
 

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