Booster Heater for Design Day Failure?

gasfolk

Some remaining venting issues, but based on *real-time* design-day boiler clocking, we are close to specifying a very, very small replacement boiler--much smaller than Manual J estimates.

The house has four electric strip heaters (10 MBH in the attic, 12 MBH in the basement), which are never used, but they also provide some emergency backup.

Not too late to pull back from the brink, if anyone has any additional comments, pro or con.

Many thanks,

gf

gasfolk

Is such a service available ?

If we size our new boiler by *just barely* (plus a little) covering the real-time, design-day, heat loss...

1. If the new boiler ever fails, could repairmen both fix the boiler AND (if necessary) bring some kind of "booster heaters" to reheat the house faster?

2. Is tight boiler sizing (to that degree) likely to save resources (money and fuel) on an individual and/or community-wide basis?

3. Does the minimum recommended boiler output for indirect DHW make all of this irrelevent (and what is that minimum)?

Thanks for any suggestions,

gf

gasfolk

Is such a service available ?

If we size our new boiler by *just barely* (plus a little) covering the real-time design-day heat loss...

1. If the new boiler ever fails, could repairmen both fix the boiler AND (if necessary) bring some kind of "booster heaters" to reheat the house faster?

2. Is tight boiler sizing (to that degree) likely to save resources (money and fuel) on an individual and/or community-wide basis?

3. Does the minimum recommended boiler output for indirect DHW make all of this irrelevent (and what is that minimum)?

Thanks for any suggestions,

gf

Alan(OnVacationInOregon)Forbes

Don't know

where you live, but nobody around here offers that kind of service for homes. I've seen big mechanical contractors have something ready for commercial jobs, i.e. hospitals, schools. You've just got to make do until he fixes the darn thing.

2) Tight boiler sizing means long burn times and greater efficiency.

3) Unless there's a large DHW demand, we leave the boiler sized to the heating load.

soot_seeker_2

Design Day

#2 Yes -- My suggestion... go tight, size the boiler for the heat load or even slightly less if it doesn't modulate (although not when installing boilers for cold-blooded lawyers ). If you go below design or even if you have a system that can't quite cope at design what's the big deal if the house slips down to only 65 a day or two a year? You could always spot heat with a small electric heater if that happened.

joel_19

size

a bigger boiler would probably not bring the house up any faster anyhow since it would be limited by the radiation output . Besides in that scenario if it took an extra hr to get back to 70 who cares? your real concern is getting the heat back on period so the pipes don't freeze . Never size up for domestic buy abigger tank instead.

gasfolk

Thanks for your replies

Some remaining venting issues to solve, but based on *real-time* design-day boiler clocking, we are close to specifying a very, very small replacement boiler--much smaller than Manual J estimates.

The house has four electric strip heaters (10 MBH in the attic, 12 MBH in the basement), which are never used, but they also provide some emergency backup.

Not too late to pull back from the brink, if anyone has any additional comments, pro or con.

Many thanks,

gf

hr

Boiler sizing and heatloss calcs

are, and will always be, a guess to some extent. It's hard to know weather trends, home construction and homeowners actual use patterns.

So we all chose design programs and inputs we are comfortable with and have served well over the years. Yeah, most have a bit of overkill, so sizing to the exact calc should allow some error.

I agree with your question regarding DHW. It is and will continue to be the bigger load as building envelops tighten and home size shrink. Personally I feel 50K would be a minimun size for DHW production for what we consider an average family DHW load.

As I calculate loads on modern ICF jobs I'm seeing loads around 12 BTU/ ft. So a mere 30K load for a 2500 foot home at design day, which we rarely see around here anymore!

Modulating or step fired boilers make this "unknown or variable load" easier to design around.

It's very simple to add a couple spare tee to allow a backup electric boiler to be plugged in. Heck you could carry a Thermolec under your arm, find a 30- 50 amp circuit (dryer or range) to plug into and provide backup heat.

For the cost of those small electric boilers, and the crazy fuel prices out there, why not offer a dual fuel system in the original proposal. Now you have a back up the the ability to chose your fuel source.

hot rod

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