Posted By TomAndersen on 02 Mar 2010 02:40 PM
You might want to consider whether to put the ducts in the ceiling or floors. Heat rises. Cool air sinks.

Just one small point to remember... HOT AIR, not heat,  rises. Heat goes to cold. Up, down or sideways... Heat always goes to cold.

Bergy

Posted By joe.ami on 02 Mar 2010 10:07 AM
" Most homes I evaluate have ducts that leak like crazy, and installing a high efficiency forced air system that is battling 30-50% energy loss through duct leaks is just plain stupid."

That depends entirely on where the ducts are.......
In my area unfinished basements are common and while people don't want them at 70* they don't want them frozen either. Duct loss was commonly employed to temper these spaces as the load is modest. To seal up every last joint and then cut a hole in the duct and add a register to heat the basement is a 0 net gain.
Duct sealing makes much more sense to me in attics, crawls or basements in cooling dominated climates.
Code now requires the sealing of joints.
j

Joe - your point is well taken. I'm referring to leaks outside the conditioned space. OTOH, I'm a believer in designed delivery rather than random leaks. If ducts leak, inside or outside the conditioned space, then the desired airflow isn't getting to the intended space. I see most of the worst problems being on the return side with the occasional disconnected supply duct in the attic. I've found that code mean little. Unless there is a quantitative measure to back it up, many builders/contractors won't do the job properly.

Sorry for the long time lapse. I've got a newborn and time seems to be scarce right now.

Geome - I've asked the contractor to do me a comparison of geo vs. ASHP. No reply from him yet.

Joe.ami - I'm in Iowa. On the sizing thing, can we have the whole house radiant with a 38K unit and supplement with electric resistant forced air? How would that work? Also, our ductwork is in the basement, but our house design instead of a second floor, we put it in the basement with a walk-out, so it is going to be finished and the kids bedrooms are downstairs, so duct leakage is not much of a concern for us, other than to make sure they don't leak so bad the farthest BR won't get air or something like that.

Martyrh - with the tax rebate the end cost of geothermal is about $6K to 8K more than air source pumps quotes, which is why I'd like to know if it is worth to go with geo for that extra amount of money.

Tom Andersen - our heat loads for the basement are 14K and about 26K to 28K for the main floor (depending on the contractor doing the load). The thing is that two contractors that I've asked have told me this: To do whole house forced air - 3 ton unit with electric aux. To do forced air heat main floor, basement radiant - 3 ton unit with electric aux forced air. To do whole house radiant heat - 5 ton unit. To me that does not make sense that I have to upsize that much. When I ask they say it's because water heating is more demanding, though they can't explain why. I think it's because they don't know about radiant and to cover their behind they say I need bigger unit. Both also made the comment that with the radiant heat in the basement on, the forced air upstairs won't kick in as much since the basement will heat up the upstairs as heat rises. The problem with that is that there's no hot air in the basement
We have a woodburing fireplace as back up.

Heat pumps concentrate heat: The greater the temperature difference, the less heat you will get out of a unit. If you use lots of radiant floor, and can get the house heated with 95 deg in floor water, and compare that to a forced air system that needs to get the air to a higher temperature than that, then you will get more heat from a 3 ton radiant system than a 3 ton air system. The more radiant floor tubing/area you heat - the higher your efficiency and the more heat you get, as the delivered water temperature to the floor can go down.

If you put a 3 ton radiant in, then put in an undersized electric furnace with the a/c - ducting from the ceiling. Then you get heat coming from down low, and cool air falling from above - the most comfortable combination. Since you have a woodstove, you need ducting for a HRV anyway. Just make the HRV duct work big enough to accommodate the electric furnace / a/c combination. Put radiant in the entire basement, the baths, entrance way, kitchen, etc on main floor. The emergency heat is the electric furnace coming down from the ceiling. Just set its stat lower than the regular one for floor heat.

Just an idea of course! You will have to get a contractor to more than agree with any plan you may have. If the HVAC installer does not LIKE the install they are doing, then its likely you won't too.

--Tom

Boontucky-girl;

May I ask where in Iowa are you? Our company is located in Cedar Rapids. If you are in this area we would love to discuss your system with you.

Bergy