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markcr 04-18-2011 10:37 AM

Small 2 Bedroom, 900 sq. ft. Home HVAC System Questions
Hi. I'm brand new to the forum, so hello. My wife and I just purchased a small 2 bedroom home. It's a little over 900 sq. ft. living area. It has no HVAC system in place. Heat is via a wood burning stove in the living room and there is a small whole house fan in the hallway ceiling for cooling the place. The good news is that the area under the house is huge! I can stand up in most places and even the most difficult to reach spot only requires me to bend at the waist to prevent me from hitting my head on the floor joists. I have propane and 220v power available. I'm also very good with construction. I worked as a union framer for nearly 10 years when I was much younger. I'd like to install a simple HVAC unit in the house. By simple I mean, I don't need any special air purification or multiple zones, etc. I want simple heat and simple cool air. I'm envisioning the duct work running under the house and into floor registers - one in each bedroom, on in the living room and probably one in the kitchen/dining room area for a total of 4 registers. Can I install the duct work myself using flex duct? What size furnace/compressor would I need. Where would the furnace need to be located? Do they make a furnace/compressor all-in-one unit? I'm sure I'll have a lot more questions but this is my first round. Sorry for the long winded post but I wanted to get as much information out there as possible.

Blondesense 04-18-2011 11:13 AM

I don't have any answers, but may I make a suggestion. Please put your location in your profile. It can make a difference when asking about HVAC, insulation, etc.

markcr 04-18-2011 11:31 AM

I'm in Northern California. Summers get up to 95 in July and August. Winters get down in the high 20's - low 30's occasionally but not for very long periods of time. I'd like to be able to keep the home in the low 70's when I need to.

JJboy 04-18-2011 11:54 AM

I think you need to do a load calc first.

clocert 04-18-2011 12:10 PM

In general, 500 sq ft per ton, so you need 2 tons. but it all depends on how good is the house insulated. like said, load calc is a good start. If I were you, I put the air handler in the basement which will have both evaporator coil and heat exchanger, and put the condensor outside near the air handler. Flex duct is OK. You also need to plan the return air duct..size , location, etc.. there are lots of design work. have you thought about heat pump ? may be you need to discuss the whole thing with an A/C tech before you start doing anything.

markcr 04-18-2011 12:53 PM

Hi clocert. Yeah, consulting with an AC tech is my next step. In fact, I'm considering talking to a contractor about paying to have the system designed and then I can do a lot of the installation work (if the contractor would be willing to take on a job like that). I'm realizing that there is a reason there is so little information about DIY HVAC online. This is not your average layman's work. The more I research, the more I'm finding how much goes into these HVAC systems. Looking at that little register in a bedroom that spits out hot and cold air is like looking at the tip of an iceberg.

Marty S. 04-18-2011 04:41 PM

Seal the place up good and make sure it's insulated. After that a ton and a half heat pump with 5 KW of electric heat strips will be more then enough. Plan on at least 6 registers to get enough air flow across the coil.

markcr 04-18-2011 07:05 PM

Thanks Marty. The home is very well insulated and has double pane windows. I will have to make sure the old whole house fan seals (or just remove it and use the cut-out for the air intake). I appreciate the tip on 6 registers.


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