How to size a pump for hydronic heat

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Old 10-08-06, 11:23 PM
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How to size a pump for hydronic heat

How are circulation pumps sized? I found very fancy calculations for the HVAC classroom at www.engineeringtoolbox.com which seem rather cumbersome in the real world where I don't want to go through three pages of abstract calculations.

I'm wondering about an over the thumb ballpark sizing scheme. For instance I have ~20 feet of 3/4" baseboard plus 40' of copper supply and return pipe and about a dozen 90's Can I get away with a 1/25th hp pump and 5 gal expansion tank?

I have this breezeway attached to the house which is unreachable via the forced air heat in the house. I'd like to use a 60 gal electric water heater and some baseboards to heat this uninsulated space ocassionally. Answers or resources for finding the answers would be most be welcomed.

Thanks in advance for any replies

Erich
 
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Old 10-09-06, 05:36 PM
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Circulator sizing

1Silica: Most water heaters are not approved for space heating.
That being said, why would you want to use an electric water heater anyway. If you are going to use electricity, why not just put in electric baseboard? If this is the same water heater you use for domestic hot water, the only way you could do it that I know of is to have an external heat exchanger. The baseboard will not stand the pressure of domestic water & the domestic will eat the thin tubing of the baseboard in nothing flat.

Zaq123: I'm going to split off your question to a different thread entitled "circulator for indirect".
 
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Old 10-09-06, 07:40 PM
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It seems that I got the moderator upset, I apologize. I was hoping not to have to argue the details surrounding my question. It seems that I may have to anyway.

1) Of course you are correct in that most water heaters are not apporved for space heating. When this system is complete it will be solar with Approved electric backup. The 60 gallon is to tide me over till the full system is online.
2) I want to use an electric water hearter because electric baseboards are a dead end. Hot water baseboard can be heated with whatever heats water, solar wood electric etc.
3) I'll be storing the heated water in an additional insulated tank and will not run the heat elements during on peak rates (ocassional daytimes) I'm on time of day rate metering so evenings my rate is 1.8 cents/kw daytime it's 14 cents.
4) this is the first zone in what will eventually be a whole house multi zone hydronic heat conversion from forced air to solar with electric backup
5) This water heater is not tied into the the domestic hot water in any way. it will be a closed system.

All this being said I hold my hat in my hands and ask my original question again in a most humble and contrite manner:
How does one produce a rough estimate of an appropriate circulation pump size? I have ~20' of 3/4 baseboard, 40' of supply, a dozen 90's and about 4' of head.

Erich
 
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Old 10-09-06, 07:57 PM
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Hat, schmat.... Get over it. I don't think the moderator is annoyed, just seems this kind of question comes up here periodically and without the rest of your context, it did indeed seem a foolish endeavor to set up a hydronic system for 20 ft of heating element. Now that we see the larger picture, it makes a bit more sense.

A heating zone like you describe would have a total equivalent length (straight pipe, element, elbows, a valve or two) of about 90 ft. At 4 gpm, your head loss would be about 2.8 ft. A Taco 006 could do that. A 003 would probably work but might come up a little short. See http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf if you want the scoop on a less-than abstract calculation. Takes about 10 minutes to set up in a spreadsheet.

There is a rule of thumb for sizing circulators, but it's so bad that I'm not going to share what it is.

If you are doing a scorched air to hydronic changeover, you might also consider an oil, gas, wood, or other-fired boiler backup instead of electric.

I take it you are doing all your building load calcs, storage needs, etc. for the solar. The electric too for that matter.
 
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Old 10-10-06, 08:05 AM
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Thank you for the reply xiphias. The link to the taco pdf looks great, easy enough to run through and it outputs a real world result.

The building load and storage needs as well as alternatives to electric backup will be addressed by the solar contractor after the new insulation, windows, roof and vapor barrier are finished, that's my job. Currently my 130 year old farmhouse heats up the great outdoors way too much to consider the changeover until the heat load is reduced. I wanted to get a jump start on this 10 year long project.
 
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Old 10-10-06, 04:49 PM
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1silica

No you did not upset the moderator. He was just trying keep you from running afoul of codes & other regulations, to say nothing of wasting a pile of money on an electric water heater. The additional information you provided certainly cleared the waters. Peace
 
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