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8 Answers

Wall vent vs. roof vent

We are installing a custom wood range hood and can't decide between venting through our wall or heading through the roof. The duct is 6" round. Going through the roof the run would be about 3-4' straight up. Roof is pitched about 5-12 and the vent cap would land right around 30" from the eave.

The range sits on an exterior wall, so heading though the wall would give the run a 90 degree turn and about 2' of ducting. The siding is 4" lap fiber cement. Any pros or cons or suggestions to persuade me one way or another?

Asked By Matt Cibula | Jan 25 15
2 Answers

What's the best way to integrate rain water to a condo system?


First of thank you for having such a wonderful forum to share infornation on. I have found this place very usefull in the past.

To my question: im designing a 7 story medium sized condo that will house 6 families. Im thinking of integrating rain harvesting to the building as we some times get droughts and i hate to see all that rain water go to waste. I think it should be regulation to have some sort of backup water sytem just incase the mains dry up. But for now will just be using rain water for the watering closet.

Some numbers:

Asked By Osman Naskali | Jan 24 15
22 Answers

Best HVAC for a 1,100 sq. ft. passive solar house at 46 N latitude?

We are building high-performance, all electric, 1,100 sq foot passive solar home in cold weather winter climate with hot, humid summers. Slab on grade. Exposed concrete floor as thermal mass. Natural gas is not available. Winter temps infrequently reach -20 to -30 degrees range in December and January. We will use modeling to size heating and cooling system. We will have two bedrooms, open living, dining, and kitchen (primary solar gain area). In addition, there will be a full bath, 1/2 bath, mudroom, and mechanical room. Heating days the last 3 years: 7,065; 8,980; 9,799.

Asked By Randy Bunney | Dec 26 14
3 Answers

What is the calculation method to determine the actual BTUH output of a hydronic radiant floor?

We are looking for a mathematical calculation for determining the actual btu output of a hydronic radiant slab floor in a basement. Any assistance is greatly appreciated.


[The author of this question has asked for his name to be omitted.]

Asked By GBA Team | Jan 16 15
1 Answer

How to optimize HVAC ducting

I will be building a new home in Idaho in an area not serviced by natural gas. Most new homes there use electric heat pumps. In brief, super insulated and well sealed 2400 SF with 900 SF attached garage, 750 SF bonus room, conditioned crawl space, vented attic. I’ve never worked with heat pumps or ducting before. I’m uncomfortable turning the design over to an HVAC contractor without specific instructions. Two have told me the air handler will be placed in the garage and return will be through the (unconditioned) attic.

Asked By Dick Lowman | Jan 14 15
12 Answers

Can I make mini splits more efficient at extreme temperatures?

I renovated a home in northern New Hampshire with meaningful air sealing and additional insulation. I installed Mitsubishi hyper heat mini splits upstairs and down, but have baseboard and wood stove backups for when the temperatures drop below 20f and the mini splits need help. Overall, I am happy.

My question is about the outdoor units. Below a certain outdoor temperature the mini splits lose some energy efficiency.

Asked By Phillip Roshak | Jan 14 15
11 Answers

Boiler water temp not matching aquastat setting

I have a hydronic heating system- mostly cast iron radiators and a couple cast iron baseboards and 3 copper fin baseboards. Aquastat is set to 190*. Water temps only get to 150* before the boiler shuts off. Radiators throw heat, but the baseboards need hotter water to be effective IMO. In any event, I'm not sure where to look first. Can this possibly an issue with my programmable thermostat? The room reaches the temperature it need to, to satisfy the thermostat. Thanks

Asked By Ric Pasqua | Jan 12 15
6 Answers

Closing vents in unused rooms

My local utility had the following info on it's web site regarding closing vents in unused rooms. Any contrary thoughts on this?

"It’s true that closing a vent or two may reduce the furnace’s efficiency slightly. But if you’re closing a vent to avoid heating an area that doesn’t need to be heated, the energy you save will be greater than the energy lost due to the slight increase in inefficiency.

Bottom line: If you don’t need to heat a room, close the vents in that room."

Asked By Stephen Martinson | Jan 5 15
1 Answer

Two layers of R4.2 on attic ductwork

Hello all,

A client just had her ducts insulated. Unfortunately, the HVAC company installed R4.2 instead of R8 and to 'ease' the repair just wrapped another layer of R4.2 over the existing layer. Now I'm concerned about condensation or vapor lock here in Chicago (hot summers and cold winters). Should I/we be concerned and should it be fixed or is the risk relatively low? The ducts are rigid and mastic-ed at every junction. Thanks...Ross

Asked By Ross Neag | Jan 12 15
3 Answers

Heat pump COP vs. capacity

A while back Marc Rosenbaum mentioned tuning his heat pump to more closely track the needed capacity in heating mode, and reported significant efficiency improvement. I dug into the documentation for the Daikin here and while it doesn't really have truly *variable* capacity in heating mode -- it tends to just run full-blast because there's no issue about latent load -- it does have a "demand" setting which simply reduces the output to a configurable percentage. This is either a fixed setting or can be externally switched in and out via wired control from, say, a building-management system.

Asked By Hobbit _ | Jan 8 15
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