Need schematic or help with an OLD oil fired "Delco Heat" Boiler


Old 04-27-12, 02:44 PM
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Question Need schematic or help with an OLD oil fired "Delco Heat" Boiler

My daughter bought a house with an OLD "Delco Heat" brand oil fired boiler. It is model DB3W. It has a TACO 1219A tankless water heater installed. They went to an electric water heater, and I need to know how to disable the tankless so it won't call for heat, only the house t-stat.

If anyone has any info, I will be extremely grateful!

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Old 04-27-12, 06:18 PM
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A tankless water heater (internal coil type) does not make a call for heat in order to heat the HW. Instead, the boiler is kept at or above a set minimum temperature ("low limit") which keeps the boiler water surrounding the tankless coil hot, so that there is always domestic hot water available on demand (or at least that's the theory). This is referred to as a "warm start" boiler arrangement.

A "cold start" setup is different in that the boiler temperature is NOT kept above any minimmum temperature, and therefore it does NOT utilize any low limit control. So long as there is no call for heat, the boiler temp can fall all the way down to to room temp.

It sounds like you may be asking how to switch your boiler from a warm start to a cold start arrangement. That is doable, but you have to first consider the age of the boiler. There is some concern that older, higher mass cast iron boilers that have been kept warm for 99.999% of their existence might develop leaks when they are converted to cold start status (think greater expansion and contraction of the cast iron).

Of more concern, there can also be issues with condensation if the temperature of the water returning to the boiler falls below a certain temperature (130* or so).

Flue Gas Condensation - This is a condition when the water in the boiler is cold enough and the flue gas temperature going through the boiler is cooled to a point that we encounter condensate. The average return water temperature where this takes place is below 130f. This is what we call the flue gas dew point temperatures. This is similar to a cold drink in the summer and the glass sweats. It has cold drink inside and hot humid air outside or another example is the ground gets hot during the day and the night cools off. If the conditions are correct by morning we have dew on the grass. We cannot change physics but we can change the conditions and keep it from happening since it is all temperature related. The cast iron or steel boiler is always inputting the same flame temperature the change must be in gallon per minute (gpm) flow through the boiler. Slow the water down in a boiler and the water gets hotter.

The bigger problem with flue gas condensation is what is included in the byproducts of combustion. Among others chemicals there is hydrochloric acid, carbonic acid and sulfuric acid. When the boiler is allowed to continually condense in the flue passes the acids are eating at the iron or steel. When the flue passes dry out, the acids become basically dormant. This is also a good reason to have the gas or oil boiler cleaned every year. There are boilers today designed to condense therefore made of materials that resist the effects of the acids. These boilers are made of cast aluminum and stainless steel. Source
Just something to think about.
Old 04-28-12, 11:55 AM
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Thank You Rockledge!!
I assumed, (and you know what assume does) that the tankless would call for heat just as the room thermostat does. Since it doesn't, we can resume heating the house as usual, and let the new water heater take over for the tankless. We will leave the old boiler in it's warm start configuration.

Thank you for the info!

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