Boiler Size for Design Temp

Neil_5

As a homeowner with a hot water gas system, I am trying to understand how these systems are designed and intended to be used.

I read a lot about boilers being oversize. If the design temp is lets say 10*. At this temperature, how does the boiler operate? It fires up and keeps the flame on until the house reaches the thermostat setpoint? Or it fires up and heat the water up and turn off but keep the circulator on and fires again when the delta on the aquastat calls for heat?

I am trying to understand how a boiler operates at design temprature when size correctly.

Thanks,
Neil

Dale

All the time

All the time, the boiler never shuts off and that is GOOD. At design temp the heating unit, whatever it is, puts enough heat into the house to keep the house at 68 degrees F ( or what you choose for indoor design temp) to exactly match the heat leaving the house at 10 F or whatever your outdoor design temp in other words at a approx. 60 degree delta t. I personally know of only one house where this happens, all the others I know cycle off for some period even at -10, about the outdoor design here. So almost everything is oversized. Mechanical things like to run, not start and stop = a cycle. Ignitors for instance are good for so many cycles, motors float on a magnetic field when running and pull much higher current when starting. Heat exchangers expand and contract on and off, all have a wet time before they dry out.

Neil_5

My Situation

Here in Long Island NY, the temp is around 12* and my boiler with outdoor reset is cooking along at 190 deg water. But boiler fires up and heat water to 190 then turn off and keep the circulator on. Would I have a longer run time if I had more emitters? or maybe raise the basement zone temp?

Thanks for the info
Neil

Dale

set up

So, your boiler burner keeps the water temp at whatever the IO aquaset set point is and the pump is cycled by the stat? You may have a hot start boiler where the stat controls the pump. To make the world of hot water heat somewhat confusing there are many many ways to control a boiler burner and boiler pump. Some systems start cold but keep the pump running after a call for heat ends. Some systems only allow the pump to start if the boiler is at some given temp. also how do you get your domestic hot water. I don't know anything about LI other than that Ron Jr. and Dan live there but it seems there's alot of domestic hot water from boiler coils there which is perhaps why the 190 F temp. If you don't need it for domestic you can adjust the IO to a different curve to get by with a lower water temp. which it sounds like will work for you.

Neil_5

I have an DHW gas fired heater by itself. No, the boiler is cold start, the STat controls the zone valve. The Tekmar controler sets the temp of the water. Its at max now because of the outside temp and it is barely keeping my house at 72-73. Older house, insulated but need to insualte the basement and some small leaks. Attic is well insulated and walls etc.

So far it maintained the house at 72 with an outside temp of 6* using 190* water, but the circulator is on all the time and the boiler fires more frequent to get the water to 190 and then shut down.

Ernie

Neil

What type of heat emitters do you have?

Neil_5

Emitters

The den/living rm/dinning rm/all bed rooms have cast iron convectors, the kitchen and 3 baths were updated and have baseboard. Love the output from the convectors. The entire system is ran off a monoflo system and works well.

Except for the den, usually a bit chilly, lots of windows, tried to minimize draft as much as I can, will have to change the storm door in the den.

Neil

Ernie

Tekmar Control

Neil I am no expert, just a HO like you, but do all my own installations. Recently installed a Tekmar 260 control and have fin tube convectors in all rooms, however they wrap the entire exposed perimeter walls, except for living and dining/kitchen rooms which have double French Doors across a 40+ foot span. This morning it was 8*F and my boiler temp was running in the 160*+ range. I changed my emmiter setting on Tekmar to base board convertors to more reflect the orginal temperatures I ran on manual controls, still playing with temp settings. Its strange that you should not be able to get your indoor temps higher than you indicate with 190* water. How many square feet are you heating? Maybe Ron Jr. will jump and help out.

Neil_5

Sq Ft

Am heating 1700 sq ft, man 160 heating with 8* outside, thats a tight house man, new?

Ernie

Old House

Remolded in 1985, 2000sq ft total; downstairs is the living, dining, kitchen area with powder room tucked under stairs,utility room is behind this in a 6'X 36'x10'space all slab on grade with hard wood floors on 2x4 sleepers with expanded polstyrene foam in between except utility which is concrete floor with drains. Ceiling above is R-38,walls R-13 & R-19,all interior walls also insulated to r-13,attic R-19.