Residential boiler manifolds - is 1 1/4 overkill ?

bill_97

in 1 1/4 inch for the supply and return for years . The vast majority of homes we work in need much less than 100,000 btus ( normal size oil boiler we install - max firing rate ) .

I'm not the smartest guy when it comes to flow rates and delta tees and the rest ..... But given the fact the heatloss is small for these homes is there any reason we shouldn't be using 1 inch for the manifold piping ?

Thanks in advance .

Robert O'Brien

Ron

1 1/4" can carry 140K Btu/hr.1" can carry 71K BTU.So,it depends on the situation.More than half the boilers I do are in houses with less than 71K heat losses.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Home Depot Employee

Alot of ratings you see published or quoted are based on 100'. Many times 1' copper for near boiler piping such as a header is fine for up to 150K.

JackR

1\" Pipe

Will carry roughly 80K based on 100' of pipe, if you are using it as header off of the boiler you can easily achieve 100K without any problem. I

Brad White_194

Personally,

I use 1-1/4" if it matches the boiler tapping size. Material cost aside, I choose not to expend pressure drop on the boiler side, but this is a reflection of my fondness for 4-way valves more than anything.

If using circulators for zoning (nothing I recommend these days due to electrical usage), the larger header exhibits less variation as zones call and cease. Also air release seems better with the lower velocities.

All that aside, if you are using a single circulator (especially a variable speed one responding to Delta-P and using zone valves -and if you are not, why not??? , a 1" main should be fine for 60-80 MBH with a 20 degree delta-T and 120-160 with a 40 degree delta-T.

My $0.02

Brad

bill_97

Thank you

for your insight guys .

Most boilers we use have a 1 1/2 inch supply tapping and either 1 1/2 or 1 1/4 return port . The part of the supply that I would decrease to 1 inch would probably be less than 2 feet total - enough for an air scoop and the circs . The return we do in copper and usually tee all the returns at ceiling height .