mod/con sizing

Mike T., Swampeast MO

Have you estimated your DHW requirements? Both peak flow and demand over time?

How many occupants in the house? Expected to change in the near future? How many bathrooms? Any unusual loads like a very large bathtub or shower with high flow ability?

Bob_36

mod/con sizing

I am interested in a mod/con boiler. My heat loss is under 50k. The munchkin 50t or 50m would fit the bill, but if I want to add an indirect water tank I am told I need to upgrade to an 80t or 80m. My question is whether it is better for fuel savings, as well as the operation of the boiler, to upgrade to the larger boiler, or stick with my independant water heater and a 50t unit. Thanks in advance for any suggestions.

S Ebels

One option would be.....

Go with the T-50 for heating only and use a tankless instant on water heater for your domestic ala... Takagi or similar. AFA tankless heaters go, I like the models with induced draft over B-vent or chimney vent types. A TK-S1 Takagi will do a normal single family home 9 times out of 10.

jp_2

I'd just go with the T80 & indirect, make it simple, not complex......

are you sure the T50 wouldn't work as well? design days don;t seem to be the norm. and you are not heating water as often as you are heating the house.

Mark_46

Just for reference

I had the same situation with my home. I chose the 80m because of the indirect requirements.

Ken_40

Not so.

The 50 is fine. The 80 may be a tad overkill, but the 50 will work just fine!

Think about it...

A plain-jane water heater makes enough hot water for a typical family of 4 with two showers going. It has a 34,000 BTU input, 60% efficient flame under it.

You could buy a 40-gallon indirect, driven by a 50,000 BTU boiler, with 95% efficiency!

That implies you would get almost double the hot water, with the same 40-gallons of storage (the plain-jane getting a net output of ~21MBTU's; the Munchie, about 48MBTU's)

No brainer. Buy the indirect lad. It's a win, win situation.

Nick S

T-50

The T-50 actually ramps up to 80,000btu for domestic hot water heating with the Vision 1 control. Also, the T-80 goes up to 100,000btu for hot water.

Ken_40

Last I installed one...

Only if you order THAT particular model (with that feature).

Nick S

> Only if you order THAT particular model (with

> that feature).

Nick S

T-80 or 80M

I think the "T" models are the only ones that do this. The standard "M" models do not.

Bob_36

Thanks for all the replys. I called HTP, and they said, if you go with the indirect,you need to install a t80. It is just my wife and me with one bath, nothing exotic. I have a 40 gal. heater now and we never have a problem with enough water. I intend to replace it with the same size. For these conditions, do you think I should be ok? Also if I choose a Buderus g142/24 instead,(the smallest mod/con), would that be too large for my heat loss? Thanks

hot_rod

I have an 80K mod con

paired to an old Triangle Tube 32 gallon indirect and we get all the hot water my wife an I can flow. Dishes, clothes washer, tub and shower almost every night without a problem.

If you don't have a large dump load requirement, like an oversized tub, I feel the small, 40 gallon or less, indirects are the best match for an under 100k mod con. very quick recover should you ever get ahead of it's continous flow rate.

hot rod

KAG

T80M

I have the t80m with a 50 gallon Bock indirect, radiant 1st floor and baseboard 2nd floor. 6 people in the house with a 6', 20" deep soaking tub, washer machine running each day (4 kids 4-12) and I have enough hot water every day. I also DID NOT take advantage of the extra btu output of the boiler. I believe the t50m with a 40 gallon will give you enough heat and hot water, if you think you need more hot water go up to a 50. If you add Vision 1 to the system I think you will be happy with your gas bills for a long time.

Bob_36

Thanks for the input. I hoped I would get these positive responses. I am going to opt for the T50. I'll post some pictures as soon as the install is complete.

Mike T., Swampeast MO

I believe you've made a good decision. Conventional wisdom says that the boiler should not be oversized for DHW.

Bob_36

One last question before I go ahead with this project. I have been reading the manual, and it states to avoid installing the exaust over a walkway. The best place in my basement is against the driveway wall. Is this definatly a no no, or not a problem? Thanks for any info.

Mike T., Swampeast MO

The reason it's not recommended (really prohibited) is that while the condensate in the exhaust begins as vapor, most of it becomes liquid as soon as it hits cold outside air and you'll wind up with slick, clear, hard ice on your driveway or walkway...

I've seen similar happen with A/C condensate except instead of ice you get extremely slimy and slick algae.

If at all possible, vertical venting is preferred. Some installers will go to rather extreme measures to run vertical vents.

I've seen photos here of some amzing icicles from horizontal exhausts as well as walls/eaves and even one porch coated in nearly perpetual frost. Keep the exhausts well away from inside corners or porches --even further than recommended if the prevailing wind usually blows towards the corner or porch.

Bob_36

Thanks for the reply Mike. I sort of knew the answer before I asked the question. When you start looking around the house for that perfect location, it gets hard with all the restrictions in the install manual. I'll find somewhere to vent though. I'm set on making this work. Thanks again for all the replys.

Mike T., Swampeast MO

At least the Munchkin uses simple, inexpensive PVC for the exhaust and intake lines. If you're planning the route yourself make certain that you download the venting instructions and ENSURE that you stay within allowable lengths, including any restriction on the number of elbows regardless of equivalent length they add to the system!

Don't forget to look for vertical routes. If this is a single-floor house there's almost surely a place for vertical that will meet requirements.

Bob_36

I have a 1920 two story house. The chimney is in the center of the house. If I change to an indirect water heater, it would free up the chimney, due to nothing else being exausted through it. I checked with HTP and they said that would be an option. I'm using that as a last resort though.