Residential HVAC question

[woody]

We're in the midst of modernizing a 26 year old house, 2100 sq ft approx, the main room downstairs has a cathedral ceiling, and a ceiling fan to push or pull as need be

It has no central AC, but does have ducts for forced hot air (giant #2 oil/woodstove in the basement that takes 4' x 10" dia logs) There are three (2'x2' apprx) intake ducts and a bunch of floor outlets... In other words, the place is plumbed for moving air.

We're in the market for an electric "heat pump" heat + AC unit. Not a 'gas pack'... LPG price is through the roof here. I know we'll have to reroute the intake ducts to hook up to the air handler (I guess to an exterior wall in the basement.) The house is poorly insulated at present, but will have new windows and fresh R19 'glass batts stuffed up in the floor joists before winter, but after snake season.

What I'd like a stab at is how many tons in a HVAC unit should we be looking at, and is that a function of the compressor, air handler(fan) or both?

Maybe this belongs on "Other Tech?" If so, use the 'report post' button & I'll get it moved.

TIA

 

[Eagle]

Dunno ... on a Jeep forum, I'd say residential a/c is about as off-topic as we're likely to get.

Tons of a/c capacity is a function of the compressor and condenser, not the fan. The fan just delivers the cfm.

If your house is poorly insulated, you're going to need more tonnage than you would in the same house with insulation up to current codes/recommendations. Also, number and size of windows and doors, and orientation of windows, will also affect the calculation. I don't think anyone can (or should) just throw a number at you.

Check the web sites for a couple of the big manufacturers like Carrier and see if they have any do-it-yourself calculators on their web sites. Or call your local Lowe's and Home Depot and ask if they have any pamphlets on how to select and size an a/c setup.

One thing to remember is that your ductwork was intended for heat, so it isn't going to be as efficient for a/c as would ductwork designed and installed for a/c. Heat rises, cold air drops. Floor registers work great for heating, but they are less than ideal for a/c. This will be a real problem in the room with the cathedral ceiling, and you'll probably need to run that ceiling fan in reverse to get the cold air to fill the space.

 

[Lincoln]

Woody,

My house is a '76 era (A/C is probably that age) with roughly 1800 ft2 and so so insulation. My floors are insulated though and it has all new windows. I've got a 2 ton here and it keeps up well. The only time it runs a lot is when I open the garage door and stick my small industrial fan in the doorway because I'm a wheeny boy. As soon as the temps balance it runs like normal. 3 ton maybe?

Be careful though. Several shops around here have been upsizing peoples A/C pumps and it's causing problems (leave it to the professionals ). People are having problems with the evaporator freezing over quickly. I think it has something to do with the ducts not flowing enough air or the evaporator isn't big enough. I believe the new heat pumps have an auto reversing feature to thaw them out quickly though, but it's still a pain the butt and a waste.

 

[logdog]

Do NOT call home depot or lowes!!! Call a local HVAC contractor, most will give a free estimate. Also, call an insulation contractor and ask for an "energy" or "m e c" check. Also should be a free service. That will tell you how efficient your home is. They will measure the U- factor in the windows and doors, and the R- factor of the walls ceilings, and floors.

Your house is plumbed for the a/c just fine if you have forced air heat. It may not be as modern as a house built today, but still much better than what you currently have. A tinner will just add a condensor to your existing unit, and put a coil outside the house. A typical 3-4 ton upgrade in my neck of the woods runs around $1,800.

Good luck.