Hydronic radiant in Zone 2 (Biloxi MS) ?
Last Post 09 Oct 2018 11:33 PM by Dilettante. 8 Replies.
Printer Friendly
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Author Messages
owkayeUser is Offline
New Member
New Member
Send Private Message
Posts:19

--
08 Oct 2018 10:46 PM
We have long hot summers and relatively short winters here in Biloxi. We've been living in a 90-year old house that has no insulation and lots of 'ventilation' ... meaning lots of undesirable gaps in and around doors and windows, the base of our walls, etc. The underside of the house is completely open to the ambient temperature outside, so our floors get really cold.

The forced air heating system blows warm air from above, and this heat struggles to get to the floor, thus the temperature beneath my desk is often in the 40-50 degree range all winter -- not comfortable to my feet or legs! It's because of this situation that I dream of having warm floors in our planned new house of 1200 square feet (slab on grade).

Some people tell me it's a waste of money to install hydronic floor heating in this climate when a single mini-split could heat the whole house if it is well insulated, which it will be since we plan to use ICFs. Would you bother to install PEX in the slab of a new house in this situation?

If not, how much insulation should I use beneath the slab, if any, to help keep the floors warm enough to not feel chilly?
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
08 Oct 2018 11:14 PM
You will need AC in your climate so a mini split would be a good choice for both cooling and heating. You will probably want an ERV too. You could use HR floor heating to augment the mini split in Winter if you really want warm floors. If you do HR, you will want a little more under-slab insulation than if you didn't do it since HR results in a higher temp floor and associated higher floor heat loss. However, this tends to conflict with what would likely be better in the Summer, namely a ground coupled slab to reduce AC load. So you might want to first run the numbers (e.g., ACCA Manual J or equivalent) and give this more consideration before deciding.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
owkayeUser is Offline
New Member
New Member
Send Private Message
Posts:19

--
08 Oct 2018 11:48 PM
Thanks sailawayrb.

Ground coupling of the slab was something I thought about, but I did not think about very much, so now that you've mentioned it I think I should look into it a little more.

It seems to me that if the ground surface temperature here is cooler than my desired indoor air temperature in summer, it "makes sense" to NOT use any insulation beneath the slab, so that the slab can help cool the house. However, I am almost certain that the ground surface temperature in summer is warmer than my desired indoor air temp, which would suggest that I might want to insulate the slab so that it does not heat up the house as much as it otherwise would.

Our cold water gets unreasonably warm in the summer because the pipe it comes through is buried only 6-12 inches below the surface. In winter the water gets very cold, too. This is why I think the ground surface temp is higher than 72 degrees in summer and much colder in winter. If this is the case, it might be wise to separate the slab from the ground with at least some insulation ... and skip the hydronic floor heating.

Note that the ground temp 10' below the surface here is reportedly 70-72 degrees year-round. For this reason I've considered running my incoming water through a coil of PEX buried 10' deep in order to stabilize my incoming water temperature throughout the year. I also thought about running this water through pipes in the slab floor to help cool the house in summer, but since this water would be so close to my desired indoor air temperature it's probably not worth it to do this. Or is it?.
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
09 Oct 2018 03:12 PM
You will need to run the numbers or contact someone good in your area who does this and they will likely know straight away how best to proceed. I suspect skipping the HR will be the best option, but what you ultimately want is another factor too.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
owkayeUser is Offline
New Member
New Member
Send Private Message
Posts:19

--
09 Oct 2018 03:41 PM
I already have a coil of PEX I've never used. I can bury it in the slab now, then later if I want to try using HR floor heating I will be able to at minimal cost and effort.

sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
09 Oct 2018 04:17 PM
Yes, we always recommend putting PEX in a slab if there is any chance you might do HR. It is a relatively low cost provision to have the most efficient HR emitter...assuming you have the proper amount of under-slab insulation.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
09 Oct 2018 10:16 PM
I just realized that I neglected to also suggest that you might want to consider HR panels or walls too. There are a multitude of ways to accomplish this.

We have a recent acquaintance (Michael Frerking) who has a poured earth building module system with the HR PEX and electrical already in the building modules. We don’t currently have any first hand experience using this system, but someone here might find it interesting and a possible building option too.

Form Free Building

Living Systems Architecture

I would also very much like to hear from anyone who has knowledge of or first hand experience using this system.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
Dana1User is Offline
Senior Member
Senior Member
Send Private Message
Posts:6991

--
09 Oct 2018 10:51 PM
In US climate zone 2 (that would be Biloxi MS) there's no rationale for putting insulation under a slab that isn't used for heating, but there's a financial & wintertime comfort case for putting R5 of slab-edge insulation of a slab-on-grade house down to a depth of 1.5-2 feet below grade. See Table 2, p10 of this document:

https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf

If you're heating the slab put 1- 1.5" of EPS under the entire slab.

+1 on the recommendation for heating & cooling with mini-splits, but make sure a competent third party performs the Manual-J heating & cooling load calculations (such as a professional engineer or RESNET rater) , and NOT an HVAC contractor, or you'll end up with a "solution" so oversized for the loads that it can't operate efficiently, and will be less comfortable. The "ductless head per room" approach is really popular with HVAC contractors (they have boat payments to make, after all :-) ), but that usually raises the oversizing factor to the LUDICROUS, not merely ridiculous range.

Enclosing and insulating a pier foundation to thermally earth-couple a 90 year old house to the subsoil is a good way to go in Biloxi.
DilettanteUser is Offline
Basic Member
Basic Member
Send Private Message
Posts:494

--
09 Oct 2018 11:33 PM
You're in a predominantly cooling-driven climate. So forgoing under-slab insulation might be a better idea.

Also, if you're having that much of a temperature swing in your municipal water, when running/re-running the water line, see if you can bury the lines for your property DEEPER.
It probably won't COMPLETELY mitigate the swing. As the rest of the municipal system is still shallow.

However, you may see some cooling benefit during the summer as, when it hits your property, it dives down into a much cooler layer of soil and can bleed heat. Not really sure how much help that'll give to your winter water unless you're going shallow geothermal-field (10+ feet) levels of deep.
You are not authorized to post a reply.

Active Forums 4.1
Membership Membership: Latest New User Latest: hudson2000 New Today New Today: 0 New Yesterday New Yesterday: 2 User Count Overall: 34707
People Online People Online: Visitors Visitors: 283 Members Members: 1 Total Total: 284
Copyright 2011 by BuildCentral, Inc.   Terms Of Use  Privacy Statement