indoor temp in church

gregchurchill

The church does not maintain temp all week and then wants it 70 degrees on Sunday. Existing furnace works too hard to get there. Am sizing new furnace and am wondering how oversized must I figure to not make the furnace work so hard. Church gets down to freezing (relative to outdoor temp). Duct work can handle 2000 cfm. Existing furnace if Williamson CHB-140. Previous occupants kept it 50 ish and would bring temp up over two days. Current occupants want furnace on Sunday morning at 5 AM to bring temp to 70 by 11 AM service. Furnace is giving up the ghost- have lost two pumps and burner motors. No back pressure from furnace but components get too hot and bind up from heat transfer. Also, they have put the F&L on on all the time the furnace calls. i know Dan's rule about doing work for the church, but I am a little stuck.....

Jamie Hall

They don't want much, do they? Aside from the damage they are doing to the interior finishes, pews, floors... piano if there is one, organ if there is one...

What is the heat load like at 70? Have you got that number? Also, just how big is this place (cubic volume)?

DZoro

Sounds like your stuck, but I'd still tell ya to run

A furnace is designed to maintain temperatures. Previous occupants were doing it.... correctly. It will be almost impossible to bring the building, and contents to 70 in a few short hours.

I have a church hall that does the same, the Janitor is trained to increase temp. 2 days in advance of any activities. Not too many complaints with that. It just takes time to penetrate all the wood benches, walls, floors........ and you cant rush that time no mater what.
What size duct do you have to work with?

gregchurchill

Volume is 35k cf. load at 70 degrees is 103,927. Feed is 14x24, but return is 20x8

EBEBRATT-Ed

Why the big difference in duct size? The 20 x 8 is good for 900 cfm. The 14 x 24 is good for 2700cfm

On heating about 100btu/cfm is right so you are limited by the 20 x 8 return is good for 90,000btu.

It's close to your heat loss of 104,000 although undersized.

You can't go larger without more return air

Jamie Hall

And furthermore... since you are limited as @EBEBRATT-Ed said, you can see that there is no way you can expect to bring the space from say 40 to 70 in the time you want. There is a decent chance that you can hold the temperature, but you can't get it up there.

rbeck

Is it possible to twin two furnaces and add separate return? That way both fire in larger demands and one maintains.

gregchurchill

It's all about the almighty $$. They want magic and obviously science overrules all else. As much as I wanted to see if I was missing anything I really wanted some emotional support so I thank you all! On to fight the good fight....