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# BTU's

Member Posts: 4
edited December 2016
I have cast iron radiators in my house. I am think about installing a condensing boiler. When it comes to sizing I might assume the manufactures assume baseboard radiators are used in there calculations so how would I size? Is it true you cant mix baseboard and cast iron in the same house?

• Member Posts: 4
Ok Thanks so far. Heat loss I know nothing about. When I went to vocational school they showed us how to calculate how many btus or radiation for each room. Like how many feet of baseboard etc. How would heat loss help? I have a clue but not sure how to get it down to numbers that will help me get the nessary output btus of the burner.
• Member Posts: 9,514
First you need to do a heat loss of your home room by room.

Then you need to do a radiator survey by figuring out the SF of radiation for each room. This will tell you if each room is over radiated, or under radiated.

If you are lucky. The rooms are over radiated. Either because originally they were oversized, or there was envelope upgrades done to the home since the original heating system was installed.

Being over radiated is good this will allow you to run lower Water temps in the heating system which may allow more time in condensing mode since you are seeking a mod/con boiler.
• Member Posts: 5,078
You need to do a Manual J heat loss calculation on the building. This is the only way to size the boiler properly. Doing a radiation survey that you are talking about is only useful for figuring how to implement the system after the boiler is sized. There are several free online calculators for doing a heatloss, but I would also suggest you google Manual J and start reading to learn about what it is.
2014 Weil Mclain EG-40
Boiler pictures updated 2/21/15
• Member Posts: 7,356

When I went to vocational school they showed us how to calculate how many btus or radiation for each room. Like how many feet of baseboard etc.

Depending on the methodology, that may well have been some version of a heat loss calc you learned. Did it involve measuring walls and windows?
• Member Posts: 4
Yes
• Member Posts: 170
@intakevalve, I would recommend you start with the following two articles: (they helped me immensely when I was trying to understand what a heat loss calc was and why it was so important for heating equipment selection.)