Forced Warm Air

Bob Sweet

for wet heat by addressing the heat transfer design, however I would look to a heat loss and heat gain calc. designed spec. for F.A. Duct design is the key. Static press. cfm, and air loss can turn this into a pleasent exp. or a nightmare.

Chris_36

Scorched Air

I've been installing and servicing boilers for about 20yrs, my only dealing with warm air has been running the gas pipe to them. I'll be doing a furnace for a friend this summer and need to know if I can use the same heat loss program for warm air as hot water? I use the Slant Fin Heatloss explorer. Thanks in advance for any help

JimGPE_3

Yup.

Heat loss is heat loss. Be sure that if he wants to install air conditioning in the future that the size of furnace can handle the tonnage he will need. Sometimes that will bump the furnace up a size just to get a big enough blower.

Mike T., Swampeast MO

I don't recall an input for duct losses in the Slant Fin Heatloss Explorer.

Not at all uncommon for air leakage (particularly in the return) and transmission loss to exceed 20%.

Jed_2

Is the Duct

in a conditioned space or unconditioned space? Makes a difference. Besides, system delivery has nothing to do with the building heat loss. How the system is installed might be another matter.

Jed

GW

yeah man

It's really hard to screw up a HW system. OK, let me type that again. It's hard to 'waste' a lot of energy from a system standpoint. It may be easy NOT to get all the energy out to the system... but that's another story.

It IS really easy to waste a lot of energy with warm air/ducts/AC. 9 out 10 installers are simply clueless about fan performance, static pressure, duct loss through poor insulation and non-sealed ducts, pressure drops with air cleaners,coils, bla bla.

Ideally you want to use a heat loss program that will give you cfm's, but yes, heat loss is heat loss.

Gary

Steamhead

Arch, you might want

to get in touch with our friend Bud Goodman, the webmaster over at www.thesheetmetalshop.com . He'd know for sure if you have to make any adjustments to a standard heat-loss calc.

If this is a brand-new system being proposed, why not suggest a miniduct A/C system and hot-water baseboard? This would save the owner a lot of space that standard ductwork would otherwise consume, and use less energy to boot. I'm assuming radiant was "too expensive".....

Jed_2

Just accept it

Doesn't sound like a Hydronic system is in the cards (hydro-air or otherwise).

Jed

p.s. Maybe an ECM blower motor could save the day.

Steamhead

We never assume

hydronics is "not in the cards" on this site. But I would assume- and it looks like Gary and Mike would also- that Arch is interested in his friends' comfort and system efficiency. 20% duct loss as posted above is something I would certainly want to avoid....

Chris_36

I quess my question should have been not so much are the heat loss calcs the same, but how do I turn that into CFM. This will be a replacement of an old Thatcher, in a very old house.

don_138

divide

your btus by 30.

JimGPE_3

Then...

Check the resulting CFM against the tons of cooling he is going to need. The CFM needs to be something like tons x 400.

And duct heat loss is immaterial if the ducts are in the conditioned space. You get the benefit of the heat anyway. If the ducts are not in the conditioned space, insulate them.

Ditto for air leakage from the ducts. If the ducts are in conditioned spaces, no loss. If they are not, seal the joints.

Nuttin' to be afraid of.